use fanin_wr and fanin_rd

* revamp

* consolidate

* version bump

.devcontainer/Dockerfile

@@ -0,0 +1,22 @@
+FROM verilator/verilator:latest
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        python3 \
+        python3-venv \
+        python3-pip \
+        python3-dev \
+        build-essential \
+        pkg-config \
+        git \
+        curl \
+        ca-certificates && \
+    rm -rf /var/lib/apt/lists/*
+
+ENV UV_INSTALL_DIR=/usr/local/bin
+ENV UV_LINK_MODE=copy
+# Install uv globally so both VS Code and terminals can use it
+RUN curl -LsSf https://astral.sh/uv/install.sh | sh
+RUN uv --version

.devcontainer/devcontainer.json

@@ -0,0 +1,36 @@
+{
+    "name": "PeakRDL BusDecoder",
+    "build": {
+        "dockerfile": "Dockerfile"
+    },
+    "runArgs": [
+        "--init"
+    ],
+    "features": {
+        "ghcr.io/devcontainers/features/common-utils:2": {
+            "username": "vscode",
+            "uid": "1000",
+            "gid": "1000",
+            "installZsh": "false",
+            "installOhMyZsh": "false"
+        }
+    },
+    "remoteUser": "vscode",
+    "postCreateCommand": "uv sync --frozen --all-extras --group tools --group test",
+    "customizations": {
+        "vscode": {
+            "settings": {
+                "python.defaultInterpreterPath": ".venv/bin/python",
+                "terminal.integrated.shell.linux": "/bin/bash"
+            },
+            "extensions": [
+                "ms-python.python",
+                "ms-python.vscode-pylance",
+                "ms-vscode.cpptools",
+                "charliermarsh.ruff",
+                "astral-sh.ty",
+                "meta.pyrefly"
+            ]
+        }
+    }
+}

.github/workflows/release.yml

@@ -40,7 +40,6 @@ jobs:
       
       - name: Publish to PyPI
         if: startsWith(github.ref, 'refs/tags/')
-        env:
-          TWINE_USERNAME: __token__
-          TWINE_PASSWORD: ${{ secrets.PYPI_API_TOKEN }}
-        run: uvx twine upload dist/*
+        uses: pypa/gh-action-pypi-publish@release/v1
+        with:
+          skip-existing: true

.github/workflows/test.yml

@@ -7,10 +7,15 @@ on:
     branches: [ main ]
   workflow_dispatch:
   workflow_call:
+  schedule:
+    # Run weekly on Monday at 00:00 UTC
+    - cron: '0 0 * * 1'
 
 jobs:
   test:
     runs-on: ubuntu-latest
+    container:
+      image: verilator/verilator:latest
     permissions:
       contents: read
     strategy:
@@ -24,13 +29,30 @@ jobs:
         uses: astral-sh/setup-uv@v3
         with:
           python-version: ${{ matrix.python-version }}
+          enable-cache: true
+
+      - name: Check Verilator version
+        run: verilator --version
+      
+      - name: Install Python development packages
+        run: |
+          apt-get update && apt-get install -y python3-dev libpython3-dev
       
       - name: Install dependencies
         run: |
-          uv sync --group test
+          uv sync --all-extras --group test
       
       - name: Run tests
-        run: uv run pytest tests/ -v --cov=peakrdl_busdecoder --cov-report=xml --cov-report=term
+        run: uv run pytest tests/ --cov=peakrdl_busdecoder --cov-report=xml --cov-report=term
+      
+      - name: Upload coverage to Coveralls
+        if: matrix.python-version == '3.12'
+        env:
+          COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          uv pip install coveralls
+          uv run coveralls --service=github
       
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4

.github/workflows/typecheck.yml

@@ -22,5 +22,5 @@ jobs:
       - name: Install package
         run: uv sync --extra cli
       
-      - name: Run pyrefly type check
-        run: uvx pyrefly check src/
+      - name: Run ty type check
+        run: uvx ty check src/

README.md

@@ -1,6 +1,7 @@
-[![Documentation Status](https://readthedocs.org/projects/peakrdl-busdecoder/badge/?version=latest)](http://peakrdl-busdecoder.readthedocs.io)
-[![build](https://github.com/arnavsacheti/PeakRDL-BusDecoder/workflows/build/badge.svg)](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions?query=workflow%3Abuild+branch%3Amain)
-[![Coverage Status](https://coveralls.io/repos/github/arnavsacheti/PeakRDL-BusDecoder/badge.svg?branch=main)](https://coveralls.io/github/arnavsacheti/PeakRDL-BusDecoder?branch=main)
+[![Build](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions/workflows/build.yml/badge.svg)](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions/workflows/build.yml)
+[![Test](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions/workflows/test.yml/badge.svg)](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions/workflows/test.yml)
+[![Documentation](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions/workflows/docs.yml/badge.svg)](https://github.com/arnavsacheti/PeakRDL-BusDecoder/actions/workflows/docs.yml)
+[![Coverage Status](https://coveralls.io/repos/github/arnavsacheti/PeakRDL-BusDecoder/badge.svg?branch=tests/coveralls)](https://coveralls.io/github/arnavsacheti/PeakRDL-BusDecoder?branch=tests/coveralls)
 [![PyPI - Python Version](https://img.shields.io/pypi/pyversions/peakrdl-busdecoder.svg)](https://pypi.org/project/peakrdl-busdecoder)
 
 # PeakRDL-BusDecoder

docs/api.rst

@@ -15,10 +15,11 @@ implementation from SystemRDL source.
 .. code-block:: python
     :emphasize-lines: 2-4, 29-33
 
+    import sys
+
     from systemrdl import RDLCompiler, RDLCompileError
     from peakrdl_busdecoder import BusDecoderExporter
-    from peakrdl_busdecoder.cpuif.axi4lite import AXI4Lite_Cpuif
-    from peakrdl_busdecoder.udps import ALL_UDPS
+    from peakrdl_busdecoder.cpuif.axi4lite import AXI4LiteCpuif
 
     input_files = [
         "PATH/TO/my_register_block.rdl"
@@ -27,10 +28,6 @@ implementation from SystemRDL source.
     # Create an instance of the compiler
     rdlc = RDLCompiler()
 
-    # Register all UDPs that 'busdecoder' requires
-    for udp in ALL_UDPS:
-        rdlc.register_udp(udp)
-
     try:
         # Compile your RDL files
         for input_file in input_files:
@@ -46,5 +43,5 @@ implementation from SystemRDL source.
     exporter = BusDecoderExporter()
     exporter.export(
         root, "path/to/output_dir",
-        cpuif_cls=AXI4Lite_Cpuif
+        cpuif_cls=AXI4LiteCpuif
     )

docs/architecture.rst

@@ -1,64 +1,54 @@
-Register Block Architecture
-===========================
+Bus Decoder Architecture
+========================
 
-The generated bus decoder RTL is organized into several sections.
-Each section is automatically generated based on the source register model and
-is rendered into the output SystemVerilog RTL module. The bus decoder serves as 
-an address decode and routing layer that splits a single CPU interface into 
-multiple sub-address spaces corresponding to child addrmaps in your SystemRDL design.
+The generated RTL is a pure bus-routing layer. It accepts a single CPU interface
+on the slave side and fans transactions out to a set of child interfaces on the
+master side. No register storage or field logic is generated.
 
-.. figure:: diagrams/arch.png
-
-Although it is not completely necessary to know the inner workings of the
-generated RTL, it can be helpful to understand the implications of various
-exporter configuration options.
+Although you do not need to know the inner workings to use the exporter, the
+sections below explain the structure of the generated module and how it maps to
+SystemRDL hierarchy.
 
 
-CPU Interface
--------------
-The CPU interface logic layer provides an abstraction between the
-application-specific bus protocol and the internal register file logic.
-This logic layer normalizes external CPU read & write transactions into a common
-:ref:`cpuif_protocol` that is used to interact with the register file. When the 
-design contains multiple child addrmaps, the CPU interface handles fanout of 
-transactions to the appropriate sub-address space.
+CPU Interface Adapter
+---------------------
+Each supported CPU interface protocol (APB3, APB4, AXI4-Lite) provides a small
+adapter that translates the external bus protocol into internal request/response
+signals. These internal signals are then used by the address decoder and fanout
+logic.
+
+If you write a custom CPU interface, it must implement the internal signals
+described in :ref:`cpuif_protocol`.
 
 
 Address Decode
 --------------
-A common address decode operation is generated which computes individual access
-strobes for each software-accessible register or child addrmap in the design.
-This operation is performed completely combinationally. The decoder determines 
-which sub-address space should handle each transaction based on the address range.
+The address decoder computes per-child select signals based on address ranges.
+The decode boundary is controlled by ``max_decode_depth``:
+
+* ``0``: Decode all the way down to leaf registers
+* ``1`` (default): Decode only top-level children
+* ``N``: Decode down to depth ``N`` from the top-level
+
+This allows you to choose whether the bus decoder routes to large blocks (e.g.,
+child addrmaps) or to smaller sub-blocks.
 
 
-Field Logic
------------
-This layer of the register block implements the storage elements and state-change
-logic for every field in the design. Field state is updated based on address
-decode strobes from software read/write actions, as well as events from the
-hardware interface input struct.
-This section also assigns any hardware interface outputs.
+Fanout to Child Interfaces
+--------------------------
+For each decoded child, the bus decoder drives a master-side CPU interface.
+All address, data, and control signals are forwarded to the selected child.
+
+Arrayed children can be kept as arrays or unrolled into discrete interfaces using
+``--unroll``. This only affects port structure and naming; decode semantics are
+unchanged.
 
 
-Readback
---------
-The readback layer aggregates and reduces all readable registers into a single
-read response. During a read operation, the same address decode strobes are used
-to select the active register that is being accessed.
-This allows for a simple OR-reduction operation to be used to compute the read
-data response.
+Fanin and Error Handling
+------------------------
+Read and write responses are muxed back from the selected child to the slave
+interface. If no child is selected for a transaction, the decoder generates an
+error response on the slave interface.
 
-For designs with a large number of software-readable registers, an optional
-fanin re-timing stage can be enabled. This stage is automatically inserted at a
-balanced point in the read-data reduction so that fanin and logic-levels are
-optimally reduced.
-
-.. figure:: diagrams/readback.png
-    :width: 65%
-    :align: center
-
-A second optional read response retiming register can be enabled in-line with the
-path back to the CPU interface layer. This can be useful if the CPU interface protocol
-used has a fully combinational response path, and the design's complexity requires
-this path to be retimed further.
+The exact error signaling depends on the chosen CPU interface protocol (e.g.,
+``PSLVERR`` for APB, ``RRESP/BRESP`` for AXI4-Lite).

docs/conf.py

@@ -32,9 +32,7 @@ author = "Arnav Sacheti"
 extensions = [
     "sphinx.ext.autodoc",
     "sphinx.ext.napoleon",
-    "sphinxcontrib.wavedrom",
 ]
-render_using_wavedrompy = True
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ["_templates"]
@@ -42,7 +40,7 @@ templates_path = ["_templates"]
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path.
-exclude_patterns = ["_build", "Thumbs.db", ".DS_Store"]
+exclude_patterns = ["_build", "Thumbs.db", ".DS_Store", "dev_notes", "dev_notes/**"]
 
 
 # -- Options for HTML output -------------------------------------------------

docs/configuring.rst

@@ -1,13 +1,13 @@
 .. _peakrdl_cfg:
 
 Configuring PeakRDL-BusDecoder
-============================
+==============================
 
 If using the `PeakRDL command line tool <https://peakrdl.readthedocs.io/>`_,
-some aspects of the ``busdecoder`` command have additional configuration options
-available via the PeakRDL TOML file.
+some aspects of the ``busdecoder`` command can be configured via the PeakRDL
+TOML file.
 
-All busdecoder-specific options are defined under the ``[busdecoder]`` TOML heading.
+All busdecoder-specific options are defined under the ``[busdecoder]`` heading.
 
 .. data:: cpuifs
 
@@ -24,22 +24,15 @@ All busdecoder-specific options are defined under the ``[busdecoder]`` TOML head
         cpuifs.my-cpuif-name = "my_cpuif_module:MyCPUInterfaceClass"
 
 
-.. data:: default_reset
+Command-Line Options
+--------------------
 
-    Choose the default style of reset signal if not explicitly
-    specified by the SystemRDL design. If unspecified, the default reset
-    is active-high and synchronous.
+The following options are available on the ``peakrdl busdecoder`` command:
 
-    Choice of:
-
-        * ``rst`` (default)
-        * ``rst_n``
-        * ``arst``
-        * ``arst_n``
-
-    For example:
-
-    .. code-block:: toml
-
-        [busdecoder]
-        default_reset = "arst"
+* ``--cpuif``: Select the CPU interface (``apb3``, ``apb3-flat``, ``apb4``,
+  ``apb4-flat``, ``axi4-lite``, ``axi4-lite-flat``)
+* ``--module-name``: Override the generated module name
+* ``--package-name``: Override the generated package name
+* ``--addr-width``: Override the slave address width
+* ``--unroll``: Unroll arrayed children into discrete interfaces
+* ``--max-decode-depth``: Control how far the decoder descends into hierarchy

docs/cpuif/apb.rst

@@ -20,7 +20,7 @@ Both APB3 and APB4 standards are supported.
 APB3
 ----
 
-Implements the register block using an
+Implements the bus decoder using an
 `AMBA 3 APB <https://developer.arm.com/documentation/ihi0024/b/Introduction/About-the-AMBA-3-APB>`_
 CPU interface.
 
@@ -29,19 +29,19 @@ The APB3 CPU interface comes in two i/o port flavors:
 SystemVerilog Interface
     * Command line: ``--cpuif apb3``
     * Interface Definition: :download:`apb3_intf.sv <../../hdl-src/apb3_intf.sv>`
-    * Class: :class:`peakrdl_busdecoder.cpuif.apb3.APB3_Cpuif`
+    * Class: :class:`peakrdl_busdecoder.cpuif.apb3.APB3Cpuif`
 
 Flattened inputs/outputs
     Flattens the interface into discrete input and output ports.
 
     * Command line: ``--cpuif apb3-flat``
-    * Class: :class:`peakrdl_busdecoder.cpuif.apb3.APB3_Cpuif_flattened`
+    * Class: :class:`peakrdl_busdecoder.cpuif.apb3.APB3CpuifFlat`
 
 
 APB4
 ----
 
-Implements the register block using an
+Implements the bus decoder using an
 `AMBA 4 APB <https://developer.arm.com/documentation/ihi0024/d/?lang=en>`_
 CPU interface.
 
@@ -50,10 +50,10 @@ The APB4 CPU interface comes in two i/o port flavors:
 SystemVerilog Interface
     * Command line: ``--cpuif apb4``
     * Interface Definition: :download:`apb4_intf.sv <../../hdl-src/apb4_intf.sv>`
-    * Class: :class:`peakrdl_busdecoder.cpuif.apb4.APB4_Cpuif`
+    * Class: :class:`peakrdl_busdecoder.cpuif.apb4.APB4Cpuif`
 
 Flattened inputs/outputs
     Flattens the interface into discrete input and output ports.
 
     * Command line: ``--cpuif apb4-flat``
-    * Class: :class:`peakrdl_busdecoder.cpuif.apb4.APB4_Cpuif_flattened`
+    * Class: :class:`peakrdl_busdecoder.cpuif.apb4.APB4CpuifFlat`

docs/cpuif/avalon.rst

@@ -1,33 +0,0 @@
-Intel Avalon
-============
-
-Implements the register block using an
-`Intel Avalon MM <https://www.intel.com/content/www/us/en/docs/programmable/683091/22-3/memory-mapped-interfaces.html>`_
-CPU interface.
-
-The Avalon interface comes in two i/o port flavors:
-
-SystemVerilog Interface
-    * Command line: ``--cpuif avalon-mm``
-    * Interface Definition: :download:`avalon_mm_intf.sv <../../hdl-src/avalon_mm_intf.sv>`
-    * Class: :class:`peakrdl_busdecoder.cpuif.avalon.Avalon_Cpuif`
-
-Flattened inputs/outputs
-    Flattens the interface into discrete input and output ports.
-
-    * Command line: ``--cpuif avalon-mm-flat``
-    * Class: :class:`peakrdl_busdecoder.cpuif.avalon.Avalon_Cpuif_flattened`
-
-
-Implementation Details
-----------------------
-This implementation of the Avalon protocol has the following features:
-
-* Interface uses word addressing.
-* Supports `pipelined transfers <https://www.intel.com/content/www/us/en/docs/programmable/683091/22-3/pipelined-transfers.html>`_
-* Responses may have variable latency
-
-  In most cases, latency is fixed and is determined by how many retiming
-  stages are enabled in your design.
-  However if your design contains external components, access latency is
-  not guaranteed to be uniform.

docs/cpuif/axi4lite.rst

@@ -3,7 +3,7 @@
 AMBA AXI4-Lite
 ==============
 
-Implements the register block using an
+Implements the bus decoder using an
 `AMBA AXI4-Lite <https://developer.arm.com/documentation/ihi0022/e/AMBA-AXI4-Lite-Interface-Specification>`_
 CPU interface.
 
@@ -12,21 +12,22 @@ The AXI4-Lite CPU interface comes in two i/o port flavors:
 SystemVerilog Interface
     * Command line: ``--cpuif axi4-lite``
     * Interface Definition: :download:`axi4lite_intf.sv <../../hdl-src/axi4lite_intf.sv>`
-    * Class: :class:`peakrdl_busdecoder.cpuif.axi4lite.AXI4Lite_Cpuif`
+    * Class: :class:`peakrdl_busdecoder.cpuif.axi4lite.AXI4LiteCpuif`
 
 Flattened inputs/outputs
     Flattens the interface into discrete input and output ports.
 
     * Command line: ``--cpuif axi4-lite-flat``
-    * Class: :class:`peakrdl_busdecoder.cpuif.axi4lite.AXI4Lite_Cpuif_flattened`
+    * Class: :class:`peakrdl_busdecoder.cpuif.axi4lite.AXI4LiteCpuifFlat`
 
 
-Pipelined Performance
----------------------
-This implementation of the AXI4-Lite interface supports transaction pipelining
-which can significantly improve performance of back-to-back transfers.
+Protocol Notes
+--------------
+The AXI4-Lite adapter is intentionally simplified:
 
-In order to support transaction pipelining, the CPU interface will accept multiple
-concurrent transactions. The number of outstanding transactions allowed is automatically
-determined based on the register file pipeline depth (affected by retiming options),
-and influences the depth of the internal transaction response skid buffer.
+* AW and W channels must be asserted together for writes. The adapter does not
+  support decoupled address/data for writes.
+* Only a single outstanding transaction is supported. Masters should wait for
+  the corresponding response before issuing the next request.
+* Burst transfers are not supported (single-beat transfers only), consistent
+  with AXI4-Lite.

docs/cpuif/customizing.rst

@@ -29,15 +29,15 @@ Rather than rewriting a new CPU interface definition, you can extend and adjust
 
 .. code-block:: python
 
-    from peakrdl_busdecoder.cpuif.axi4lite import AXI4Lite_Cpuif
+    from peakrdl_busdecoder.cpuif.axi4lite import AXI4LiteCpuif
 
-    class My_AXI4Lite(AXI4Lite_Cpuif):
+    class My_AXI4Lite(AXI4LiteCpuif):
         @property
         def port_declaration(self) -> str:
             # Override the port declaration text to use the alternate interface name and modport style
             return "axi4_lite_interface.Slave_mp s_axil"
 
-        def signal(self, name:str) -> str:
+        def signal(self, name: str, node=None, indexer=None) -> str:
             # Override the signal names to be lowercase instead
             return "s_axil." + name.lower()
 
@@ -72,7 +72,7 @@ you can define your own.
 
 2. Create a Python class that defines your CPUIF
 
-    Extend your class from :class:`peakrdl_busdecoder.cpuif.CpuifBase`.
+    Extend your class from :class:`peakrdl_busdecoder.cpuif.BaseCpuif`.
     Define the port declaration string, and provide a reference to your template file.
 
 3. Use your new CPUIF definition when exporting.

docs/cpuif/internal_protocol.rst

@@ -3,10 +3,10 @@
 Internal CPUIF Protocol
 =======================
 
-Internally, the busdecoder generator uses a common CPU interface handshake
-protocol. This strobe-based protocol is designed to add minimal overhead to the
-busdecoder implementation, while also being flexible enough to support advanced
-features of a variety of bus interface standards.
+Internally, the bus decoder uses a small set of common request/response signals
+that each CPU interface adapter must drive. This protocol is intentionally simple
+and supports a single outstanding transaction at a time. The CPU interface logic
+is responsible for holding request signals stable until the transaction completes.
 
 
 Signal Descriptions
@@ -15,62 +15,49 @@ Signal Descriptions
 Request
 ^^^^^^^
 cpuif_req
-    When asserted, a read or write transfer will be initiated.
-    Denotes that the following signals are valid: ``cpuif_addr``,
-    ``cpuif_req_is_wr``, and ``cpuif_wr_data``.
+    When asserted, a read or write transfer is in progress. Request signals must
+    remain stable until the transfer completes.
 
-    A transfer will only initiate if the relevant stall signal is not asserted.
-    If stalled, the request shall be held until accepted. A request's parameters
-    (type, address, etc) shall remain static throughout the stall.
+cpuif_wr_en
+    When asserted alongside ``cpuif_req``, denotes a write transfer.
 
-cpuif_addr
-    Byte-address of the transfer.
+cpuif_rd_en
+    When asserted alongside ``cpuif_req``, denotes a read transfer.
 
-cpuif_req_is_wr
-    If ``1``, denotes that the current transfer is a write. Otherwise transfer is
-    a read.
+cpuif_wr_addr / cpuif_rd_addr
+    Byte address of the write or read transfer, respectively.
 
 cpuif_wr_data
-    Data to be written for the write transfer. This signal is ignored for read
-    transfers.
+    Data to be written for the write transfer.
 
-cpuif_wr_biten
-    Active-high bit-level write-enable strobes.
-    Only asserted bit positions will change the register value during a write
-    transfer.
-
-cpuif_req_stall_rd
-    If asserted, and the next pending request is a read operation, then the
-    transfer will not be accepted until this signal is deasserted.
-
-cpuif_req_stall_wr
-    If asserted, and the next pending request is a write operation, then the
-    transfer will not be accepted until this signal is deasserted.
+cpuif_wr_byte_en
+    Active-high byte-enable strobes for writes. Some CPU interfaces do not
+    provide byte enables and may drive this as all-ones.
 
 
 Read Response
 ^^^^^^^^^^^^^
 cpuif_rd_ack
     Single-cycle strobe indicating a read transfer has completed.
-    Qualifies that the following signals are valid: ``cpuif_rd_err`` and
-    ``cpuif_rd_data``
+    Qualifies ``cpuif_rd_err`` and ``cpuif_rd_data``.
 
 cpuif_rd_err
-    If set, indicates that the read transaction failed and the CPUIF logic
-    should return an error response if possible.
+    Indicates that the read transaction failed. The CPU interface should return
+    an error response if possible.
 
 cpuif_rd_data
-    Read data. Is sampled on the same cycle that ``cpuif_rd_ack`` is asserted.
+    Read data. Sampled on the same cycle that ``cpuif_rd_ack`` is asserted.
+
 
 Write Response
 ^^^^^^^^^^^^^^
 cpuif_wr_ack
     Single-cycle strobe indicating a write transfer has completed.
-    Qualifies that the ``cpuif_wr_err`` signal is valid.
+    Qualifies ``cpuif_wr_err``.
 
 cpuif_wr_err
-    If set, indicates that the write transaction failed and the CPUIF logic
-    should return an error response if possible.
+    Indicates that the write transaction failed. The CPU interface should return
+    an error response if possible.
 
 
 Transfers
@@ -78,155 +65,7 @@ Transfers
 
 Transfers have the following characteristics:
 
-* Only one transfer can be initiated per clock-cycle. This is implicit as there
-  is only one set of request signals.
-* The register block implementation shall guarantee that only one response can be
-  asserted in a given clock cycle. Only one ``cpuif_*_ack`` signal can be
-  asserted at a time.
-* Responses shall arrive in the same order as their corresponding request was
-  dispatched.
-
-
-Basic Transfer
-^^^^^^^^^^^^^^
-
-Depending on the configuration of the exported register block, transfers can be
-fully combinational or they may require one or more clock cycles to complete.
-Both are valid and CPU interface logic shall be designed to anticipate either.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",              "wave": "p...."},
-            {"name": "cpuif_req",        "wave": "010.."},
-            {"name": "cpuif_req_is_wr",  "wave": "x2x.."},
-            {"name": "cpuif_addr",       "wave": "x2x..", "data": ["A"]},
-            {},
-            {"name": "cpuif_*_ack",      "wave": "010.."},
-            {"name": "cpuif_*_err",      "wave": "x2x.."}
-        ],
-        "foot": {
-            "text": "Zero-latency transfer"
-        }
-    }
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",              "wave": "p..|..."},
-            {"name": "cpuif_req",        "wave": "010|..."},
-            {"name": "cpuif_req_is_wr",  "wave": "x2x|..."},
-            {"name": "cpuif_addr",       "wave": "x2x|...", "data": ["A"]},
-            {},
-            {"name": "cpuif_*_ack",      "wave": "0..|10."},
-            {"name": "cpuif_*_err",      "wave": "x..|2x."}
-        ],
-        "foot": {
-            "text": "Transfer with non-zero latency"
-        }
-    }
-
-
-Read & Write Transactions
--------------------------
-
-Waveforms below show the timing relationship of simple read/write transactions.
-For brevity, only showing non-zero latency transfers.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",              "wave": "p..|..."},
-            {"name": "cpuif_req",        "wave": "010|..."},
-            {"name": "cpuif_req_is_wr",  "wave": "x0x|..."},
-            {"name": "cpuif_addr",       "wave": "x3x|...", "data": ["A"]},
-            {},
-            {"name": "cpuif_rd_ack",     "wave": "0..|10."},
-            {"name": "cpuif_rd_err",     "wave": "x..|0x."},
-            {"name": "cpuif_rd_data",    "wave": "x..|5x.", "data": ["D"]}
-        ],
-        "foot": {
-            "text": "Read Transaction"
-        }
-    }
-
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",              "wave": "p..|..."},
-            {"name": "cpuif_req",        "wave": "010|..."},
-            {"name": "cpuif_req_is_wr",  "wave": "x1x|..."},
-            {"name": "cpuif_addr",       "wave": "x3x|...", "data": ["A"]},
-   			{"name": "cpuif_wr_data",    "wave": "x5x|...", "data": ["D"]},
-            {},
-            {"name": "cpuif_wr_ack",     "wave": "0..|10."},
-            {"name": "cpuif_wr_err",     "wave": "x..|0x."}
-        ],
-        "foot": {
-            "text": "Write Transaction"
-        }
-    }
-
-
-Transaction Pipelining & Stalls
--------------------------------
-If the CPU interface supports it, read and write operations can be pipelined.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",              "wave": "p......"},
-            {"name": "cpuif_req",        "wave": "01..0.."},
-            {"name": "cpuif_req_is_wr",  "wave": "x0..x.."},
-            {"name": "cpuif_addr",       "wave": "x333x..", "data": ["A1", "A2", "A3"]},
-            {},
-            {"name": "cpuif_rd_ack",     "wave": "0.1..0."},
-            {"name": "cpuif_rd_err",     "wave": "x.0..x."},
-            {"name": "cpuif_rd_data",    "wave": "x.555x.", "data": ["D1", "D2", "D3"]}
-        ]
-    }
-
-It is very likely that the transfer latency of a read transaction will not
-be the same as a write for a given register block configuration. Typically read
-operations will be more deeply pipelined. This latency asymmetry would create a
-hazard for response collisions.
-
-In order to eliminate this hazard, additional stall signals (``cpuif_req_stall_rd``
-and ``cpuif_req_stall_wr``) are provided to delay the next incoming transfer
-request if necessary. When asserted, the CPU interface shall hold the next pending
-request until the stall is cleared.
-
-For non-pipelined CPU interfaces that only allow one outstanding transaction at a time,
-these stall signals can be safely ignored.
-
-In the following example, the busdecoder is configured such that:
-
-* A read transaction takes 1 clock cycle to complete
-* A write transaction takes 0 clock cycles to complete
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                "wave": "p......."},
-            {"name": "cpuif_req",          "wave": "01.....0"},
-            {"name": "cpuif_req_is_wr",    "wave": "x1.0.1.x"},
-            {"name": "cpuif_addr",         "wave": "x33443.x", "data": ["W1", "W2", "R1", "R2", "W3"]},
-            {"name": "cpuif_req_stall_wr", "wave": "0...1.0."},
-            {},
-            {"name": "cpuif_rd_ack",       "wave": "0...220.", "data": ["R1", "R2"]},
-            {"name": "cpuif_wr_ack",       "wave": "0220..20", "data": ["W1", "W2", "W3"]}
-        ]
-    }
-
-In the above waveform, observe that:
-
-* The ``R2`` read request is not affected by the assertion of the write stall,
-  since the write stall only applies to write requests.
-* The ``W3`` write request is stalled for one cycle, and is accepted once the stall is cleared.
+* Only one outstanding transaction is supported.
+* The CPU interface must hold ``cpuif_req`` and request parameters stable until
+  the corresponding ``cpuif_*_ack`` is asserted.
+* Responses shall arrive in the same order as requests.

docs/cpuif/introduction.rst

@@ -2,16 +2,17 @@ Introduction
 ============
 
 The CPU interface logic layer provides an abstraction between the
-application-specific bus protocol and the internal register file logic.
-When exporting a design, you can select from a variety of popular CPU interface
-protocols. These are described in more detail in the pages that follow.
+application-specific bus protocol and the internal bus decoder logic.
+When exporting a design, you can select from supported CPU interface protocols.
+These are described in more detail in the pages that follow.
 
 
 Bus Width
 ^^^^^^^^^
-The CPU interface bus width is automatically determined from the contents of the
-design being exported. The bus width is equal to the widest ``accesswidth``
-encountered in the design.
+The CPU interface bus width is inferred from the contents of the design.
+It is intended to be equal to the widest ``accesswidth`` encountered in the
+design. If the exported addrmap contains only external components, the width
+cannot be inferred and will default to 32 bits.
 
 
 Addressing
@@ -32,5 +33,6 @@ For example, consider a fictional AXI4-Lite device that:
 - If care is taken to align the global address offset to the size of the device,
   creating a relative address is as simple as pruning down address bits.
 
-By default, the bit-width of the address bus will be the minimum size to span the contents
-of the register block. If needed, the address width can be overridden to a larger range.
+By default, the bit-width of the address bus will be the minimum size to span the
+contents of the decoded address space. If needed, the address width can be
+overridden to a larger range using ``--addr-width``.

docs/cpuif/passthrough.rst

@@ -1,10 +0,0 @@
-CPUIF Passthrough
-=================
-
-This CPUIF mode bypasses the protocol converter stage and directly exposes the
-internal CPUIF handshake signals to the user.
-
-* Command line: ``--cpuif passthrough``
-* Class: :class:`peakrdl_busdecoder.cpuif.passthrough.PassthroughCpuif`
-
-For more details on the protocol itself, see: :ref:`cpuif_protocol`.

docs/faq.rst

@@ -1,131 +0,0 @@
-Frequently Asked Questions
-==========================
-
-Why isn't there an option for a flat non-struct hardware interface?
--------------------------------------------------------------------
-SystemRDL is inherently a very hierarchical language.
-For small register blocks, flattening the hardware interface may be acceptable,
-but this ends up scaling very poorly as the design becomes larger and has more
-complex hierarchy.
-Using struct compositions for the hardware interface has the benefit of
-preserving conceptual hierarchy and arrays exactly as defined in the original
-SystemRDL.
-
-How do I know I connected everything? Structs are harder to review
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Initially this can be daunting, but fortunately the tool has an option to generate a
-flattened hardware interface report upon export. Try using the ``--hwif-report``
-command line option when exporting. This is the easiest way to quickly
-understand the structure of the hardware interface.
-
-
-
-Why does the tool generate un-packed structs? I prefer packed structs.
-----------------------------------------------------------------------
-Packed structs are great when describing vectors that have bit-level structure.
-In this tool, the use of un-packed structs is intentional since the hardware
-interface is not something that is meant to be bit-accessible. In the case of
-the hardware interface structs, using a packed struct is semantically inappropriate.
-
-... Then how can I initialize the struct?
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We get this request most often because designers want to initialize the ``hwif_in``
-struct with a simple assignment:
-
-.. code:: systemverilog
-
-    always_comb begin
-        hwif_in = '0;
-    end
-
-Of course since the struct actually is **unpacked**, this will result in a
-compile error which usually leads to the inappropriate assumption that it ought
-to be packed. (See this amusing blog post about `X/Y problems <https://xyproblem.info>`_)
-
-If your goal is to initialize the packed struct, fortunately SystemVerilog already
-has syntax to do this:
-
-.. code:: systemverilog
-
-    always_comb begin
-        hwif_in = '{default: '0};
-    end
-
-This is lesser-known syntax, but still very well supported by synthesis
-tools, and is the recommended way to handle this.
-
-... What if I want to assign it to a bit-vector?
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-Assigning the hwif struct to a bit-vector is strongly discouraged. This tool makes
-no guarantees regarding the field ordering of the hwif structure, so doing so
-should be considered functionally dangerous.
-
-That said, if you still need to do this, it is still trivially possible to
-without requiring packed structs. Instead, use the SystemVerilog streaming operator:
-
-.. code:: systemverilog
-
-    my_packed_vector = {<<{hwif_out}};
-
-
-... Why are unpacked structs preferred?
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-In the case of the hardware interface ports, unpacked structs help prevent
-mistakes that are very easy to make.
-Consider the following situation - a designer has a field that sets the following
-properties: ``sw=rw; hw=rw; we;``, and wants to assign the hardware input value,
-so they erroneously do the following assignment in Verilog:
-
-.. code:: systemverilog
-
-    assign hwif_in.my_register.my_field = <some value>;
-
-This is actually a bug since the ``my_field`` member is actually a struct that
-has two members: ``we`` and ``next``. If this were a packed struct, this would
-silently compile and you would potentially have a bug that may not be noticed
-(depending on how thorough the test campaign is).
-With an unpacked struct, this gets flagged immediately as a compile error since
-the assignment is invalid.
-
-The designer may have simply forgotten that the field is an aggregate of multiple
-members and intended to do the following:
-
-.. code:: systemverilog
-
-    assign hwif.my_register.my_field.next = <some value>;
-    assign hwif.my_register.my_field.we = <some control signal>;
-
-
-The generated output does not match our organization's coding style
--------------------------------------------------------------------
-SystemVerilog coding styles vary wildly, and unfortunately there is little
-consensus on this topic within the digital design community.
-
-The output generated by PeakRDL-BusDecoder strives to be as human-readable as possible,
-and follow consistent indentation and styling. We do our best to use the most
-widely accepted coding style, but since this is a very opinionated space, it is
-impossible to satisfy everyone.
-
-In general, we strive to follow the
-`SystemVerilog style guide by lowRISC <https://github.com/lowRISC/style-guides/blob/master/VerilogCodingStyle.md>`_,
-but may deviate in some areas if not practical or would impose excessive complexity on the code generator.
-
-
-The lint tool I am using is flagging violations in generated code
------------------------------------------------------------------
-Code linting tools are a great way to check for user-error, flag inconsistencies,
-and enforce best-practices within an organization. In many cases, linter tools
-may be configured to also enforce stylistic preferences.
-Unfortunately just like coding styles, lint rules can often be more
-opinionated than practical.
-
-In general, we will not address lint violations unless they flag actual
-structural issues or semantically dangerous code.
-Stylistic violations that pose no actual danger to the correctness of the design
-will rarely be addressed, especially if the change would add unreasonable
-complexity to the tool.
-
-If you encounter a lint violation, please carefully review and consider waiving
-it if it does not pose an actual danger. If you still believe it is a problem,
-please let us know by `submitting an issue <https://github.com/arnavsacheti/PeakRDL-BusDecoder/issues>`_
-that describes the problem.

docs/hwif.rst

@@ -1,61 +0,0 @@
-Hardware Interface
-------------------
-
-The generated register block will present the entire hardware interface to the user
-using two struct ports:
-
-* ``hwif_in``
-* ``hwif_out``
-
-All field inputs and outputs as well as signals are consolidated into these
-struct ports. The presence of each depends on the specific contents of the design
-being exported.
-
-
-Using structs for the hardware interface has the following benefits:
-
-* Preserves register map component grouping, arrays, and hierarchy.
-* Avoids naming collisions and cumbersome signal name flattening.
-* Allows for more natural mapping and distribution of register block signals to a design's hardware components.
-* Use of unpacked arrays/structs prevents common assignment mistakes as they are enforced by the compiler.
-
-
-Structs are organized as follows: ``hwif_out.<heir_path>.<feature>``
-
-For example, a simple design such as:
-
-.. code-block:: systemrdl
-
-        addrmap my_design {
-            reg {
-                field {
-                    sw = rw;
-                    hw = rw;
-                    we;
-                } my_field;
-            } my_reg[2];
-        };
-
-... results in the following struct members:
-
-.. code-block:: text
-
-    hwif_out.my_reg[0].my_field.value
-    hwif_in.my_reg[0].my_field.next
-    hwif_in.my_reg[0].my_field.we
-    hwif_out.my_reg[1].my_field.value
-    hwif_in.my_reg[1].my_field.next
-    hwif_in.my_reg[1].my_field.we
-
-For brevity in this documentation, hwif features will be described using shorthand
-notation that omits the hierarchical path: ``hwif_out..<feature>``
-
-
-.. important::
-
-    The PeakRDL tool makes no guarantees on the field order of the hwif structs.
-    For this reason, it is strongly recommended to always access struct members
-    directly, by name.
-
-    If using the SystemVerilog streaming operator to assign the hwif struct to a
-    packed vector, be extremely careful to avoid assumptions on the resulting bit-position of a field.

docs/index.rst

@@ -1,28 +1,34 @@
 Introduction
 ============
 
-PeakRDL-BusDecoder is a free and open-source bus decoder generator for hierarchical register address maps.
-This code generator translates your SystemRDL register description into a synthesizable 
-SystemVerilog RTL module that decodes CPU interface transactions and routes them to 
-multiple sub-address spaces (child addrmaps). This is particularly useful for:
+PeakRDL-BusDecoder is a free and open-source bus decoder generator for hierarchical
+SystemRDL address maps. It produces a synthesizable SystemVerilog RTL module that
+accepts a single CPU interface (slave side) and fans transactions out to multiple
+child address spaces (master side).
+
+This tool **does not** generate register storage or field logic. It is strictly a
+bus-routing layer that decodes addresses and forwards requests to child blocks.
+
+This is particularly useful for:
 
 * Creating hierarchical register maps with multiple sub-components
 * Splitting a single CPU interface bus to serve multiple independent register blocks
-* Organizing large register designs into logical sub-address spaces
+* Organizing large address spaces into logical sub-regions
 * Implementing address decode logic for multi-drop bus architectures
 
 The generated bus decoder provides:
 
 * Fully synthesizable SystemVerilog RTL (IEEE 1800-2012)
-* Support for many popular CPU interface protocols (AMBA APB, AXI4-Lite, and more)
+* A top-level slave CPU interface and per-child master CPU interfaces
 * Address decode logic that routes transactions to child address maps
-* Configurable pipelining options for designs with fast clock rates
-* Broad support for SystemRDL 2.0 features
+* Support for APB3, APB4, and AXI4-Lite (plus plugin-defined CPU interfaces)
+* Configurable decode depth and array unrolling
 
 
 Quick Start
 -----------
-The easiest way to use PeakRDL-BusDecoder is via the  `PeakRDL command line tool <https://peakrdl.readthedocs.io/>`_:
+The easiest way to use PeakRDL-BusDecoder is via the
+`PeakRDL command line tool <https://peakrdl.readthedocs.io/>`_:
 
 .. code-block:: bash
 
@@ -32,6 +38,20 @@ The easiest way to use PeakRDL-BusDecoder is via the  `PeakRDL command line tool
     # Export!
     peakrdl busdecoder atxmega_spi.rdl -o busdecoder/ --cpuif axi4-lite
 
+The exporter writes two files:
+
+* A SystemVerilog module (the bus decoder)
+* A SystemVerilog package (constants like data width and per-child address widths)
+
+Key command-line options:
+
+* ``--cpuif``: Select the CPU interface (``apb3``, ``apb3-flat``, ``apb4``, ``apb4-flat``, ``axi4-lite``, ``axi4-lite-flat``)
+* ``--module-name``: Override the generated module name
+* ``--package-name``: Override the generated package name
+* ``--addr-width``: Override the slave address width
+* ``--unroll``: Unroll arrayed children into discrete interfaces
+* ``--max-decode-depth``: Control how far the decoder descends into hierarchy
+
 
 Looking for VHDL?
 -----------------
@@ -55,10 +75,8 @@ Links
 
     self
     architecture
-    hwif
     configuring
     limitations
-    faq
     licensing
     api
 
@@ -69,29 +87,5 @@ Links
     cpuif/introduction
     cpuif/apb
     cpuif/axi4lite
-    cpuif/avalon
-    cpuif/passthrough
     cpuif/internal_protocol
     cpuif/customizing
-
-.. toctree::
-    :hidden:
-    :caption: SystemRDL Properties
-
-    props/field
-    props/reg
-    props/addrmap
-    props/signal
-    props/rhs_props
-
-.. toctree::
-    :hidden:
-    :caption: Other SystemRDL Features
-
-    rdl_features/external
-
-.. toctree::
-    :hidden:
-    :caption: Extended Properties
-
-    udps/intro

docs/licensing.rst

@@ -15,7 +15,7 @@ be contrary to this project's philosophy.
 
 
 What is covered by the LGPL v3 license?
---------------------------------------
+---------------------------------------
 The LGPL license is intended for the code generator itself. This includes all
 Python sources, Jinja template files, as well as testcase infrastructure not
 explicitly mentioned in the exemptions below.

docs/limitations.rst

@@ -1,53 +1,47 @@
 Known Limitations
 =================
 
-Not all SystemRDL features are supported by this exporter. For a listing of
-supported properties, see the appropriate property listing page in the sections
-that follow.
+The busdecoder exporter intentionally focuses on address decode and routing.
+Some SystemRDL features are ignored, and a few are explicitly disallowed.
 
 
-Alias Registers
----------------
-Registers instantiated using the ``alias`` keyword are not supported yet.
+Address Alignment
+-----------------
+All address offsets and array strides must be aligned to the CPU interface data
+bus width (in bytes). Misaligned offsets/strides are rejected.
 
 
-Unaligned Registers
--------------------
-All address offsets & strides shall be a multiple of the cpuif bus width used. Specifically:
-
-* Bus width is inferred by the maximum accesswidth used in the busdecoder.
-* Each component's address and array stride shall be aligned to the bus width.
+Wide Registers
+--------------
+If a register is wider than its ``accesswidth`` (a multi-word register), its
+``accesswidth`` must match the CPU interface data width. Multi-word registers
+with a smaller accesswidth are not supported.
 
 
-Uniform accesswidth
--------------------
-All registers within a register block shall use the same accesswidth.
+Fields Spanning Sub-Words
+-------------------------
+If a field spans multiple sub-words of a wide register:
 
-One exception is that registers with regwidth that is narrower than the cpuif
-bus width are permitted, provided that their regwidth is equal to their accesswidth.
+* Software-writable fields must have write buffering enabled
+* Fields with ``onread`` side-effects must have read buffering enabled
 
-For example:
+These rules are enforced to avoid ambiguous multi-word access behavior.
 
-.. code-block:: systemrdl
 
-    // (Largest accesswidth used is 32, therefore the CPUIF bus width is 32)
+External Boundary References
+----------------------------
+Property references are not allowed to cross the internal/external boundary of
+the exported addrmap. References must point to components that are internal to
+the busdecoder being generated.
 
-    reg {
-        regwidth = 32;
-        accesswidth = 32;
-    } reg_a @ 0x00; // OK. Regular 32-bit register
+CPU Interface Reset Location
+----------------------------
+Only ``cpuif_reset`` signals instantiated at the top-level addrmap (or above)
+are honored. Nested ``cpuif_reset`` signals are ignored.
 
-    reg {
-        regwidth = 64;
-        accesswidth = 32;
-    } reg_b @ 0x08; // OK. "Wide" register of 64-bits, but is accessed using 32-bit subwords
 
-    reg {
-        regwidth = 8;
-        accesswidth = 8;
-    } reg_c @ 0x10; // OK. Is aligned to the cpuif bus width
+Unsupported Properties
+----------------------
+The following SystemRDL properties are explicitly rejected:
 
-    reg {
-        regwidth = 32;
-        accesswidth = 8;
-    } bad_reg @ 0x14; // NOT OK. accesswidth conflicts with cpuif width
+* ``sharedextbus`` on addrmap/regfile components

docs/props/addrmap.rst

@@ -1,28 +0,0 @@
-Addrmap/Regfile Properties
-==========================
-
-.. note:: Any properties not explicitly listed here are either implicitly
-    supported, or are not relevant to the busdecoder exporter and are ignored.
-
-
-errextbus
----------
-|NO|
-
-sharedextbus
-------------
-|NO|
-
-
---------------------------------------------------------------------------------
-
-Addrmap Properties
-==================
-
-bigendian/littleendian
-----------------------
-|NO|
-
-rsvdset
--------
-|NO|

docs/props/field.rst

@@ -1,491 +0,0 @@
-Field Properties
-================
-
-.. note:: Any properties not explicitly listed here are either implicitly
-    supported, or are not relevant to the busdecoder exporter and are ignored.
-
-Software Access Properties
---------------------------
-
-onread/onwrite
-^^^^^^^^^^^^^^
-
-All onread/onwrite actions are supported (except for ruser/wuser)
-
-rclr/rset
-^^^^^^^^^
-
-See ``onread``. These are effectively aliases of the onread property.
-
-singlepulse
-^^^^^^^^^^^
-
-If set, field will get cleared back to zero after being written.
-
-.. wavedrom::
-
-    {"signal": [
-        {"name": "clk",             "wave": "p....."},
-      	{"name": "<swmod>",         "wave": "0.10.."},
-        {"name": "hwif_out..value", "wave": "0..10."}
-    ]}
-
-sw
-^^^
-All sw access modes are supported except for ``w1`` and ``rw1``.
-
-swacc
-^^^^^
-
-If true, infers an output signal ``hwif_out..swacc`` that is asserted when
-accessed by software. Specifically, on the same clock cycle that the field is
-being sampled during a software read operation, or as it is being written.
-
-.. wavedrom::
-
-    {"signal": [
-        {"name": "clk",             "wave": "p...."},
-        {"name": "hwif_in..next",   "wave": "x.=x.", "data": ["D"]},
-        {"name": "hwif_out..swacc", "wave": "0.10."}
-    ]}
-
-
-swmod
-^^^^^
-
-If true, infers an output signal ``hwif_out..swmod`` that is asserted as the
-field is being modified by software. This can be due to a software write
-operation, or a software read operation that has clear/set side-effects.
-
-
-.. wavedrom::
-
-    {"signal": [
-        {"name": "clk",             "wave": "p....."},
-        {"name": "hwif_out..value", "wave": "=..=..", "data": ["old", "new"]},
-        {"name": "hwif_out..swmod", "wave": "0.10.."}
-    ]}
-
-
-swwe/swwel
-^^^^^^^^^^
-
-Provides a mechanism that allows hardware to override whether the field is
-writable by software.
-
-boolean
-    If True, infers an input signal ``hwif_in..swwe`` or ``hwif_in..swwel``.
-
-reference
-    Single-bit reference controls field's behavior.
-
-
-woclr/woset
-^^^^^^^^^^^
-See ``onwrite``. These are effectively aliases of the onwrite property.
-
---------------------------------------------------------------------------------
-
-Hardware Access Properties
---------------------------
-
-anded/ored/xored
-^^^^^^^^^^^^^^^^
-If true, infers the existence of output signal: ``hwif_out..anded``,
-``hwif_out..ored``, ``hwif_out..xored``
-
-
-hw
-^^^
-Controls hardware access to the field.
-
-If readable, enables output signal ``hwif_out..value``. If writable, enables
-input ``hwif_in..next``.
-
-Hardware-writable fields can optionally define the ``next`` property which replaces
-the inferred ``hwif_in..next`` input with an alternate reference.
-
-
-hwclr/hwset
-^^^^^^^^^^^
-If both ``hwclr`` and ``hwset`` properties are used, and both are asserted at
-the same clock cycle, then ``hwset`` will take precedence.
-
-boolean
-    If true, infers the existence of input signal: ``hwif_in..hwclr``, ``hwif_in..hwset``
-
-reference
-    Reference to any single-bit internal object to drive this control.
-
-
-hwenable/hwmask
-^^^^^^^^^^^^^^^
-Reference to a component that provides bit-level control of hardware writeability.
-
-
-we/wel
-^^^^^^
-Write-enable control from hardware interface.
-
-If true, infers the existence of input signal: ``hwif_in..we``, ``hwif_in..wel``
-
-.. wavedrom::
-
-    {"signal": [
-        {"name": "clk",             "wave": "p...."},
-        {"name": "hwif_in..next",   "wave": "x.=x.", "data": ["D"]},
-        {"name": "hwif_in..we",     "wave": "0.10."},
-        {"name": "hwif_in..wel",    "wave": "1.01."},
-        {"name": "<field value>",   "wave": "x..=.", "data": ["D"]}
-    ]}
-
-boolean
-    If true, infers the existence of input signal ``hwif_in..we`` or ``hwif_in..wel``
-
-reference
-    Reference to any single-bit internal object to drive this control.
-
---------------------------------------------------------------------------------
-
-Counter Properties
-------------------
-
-counter
-^^^^^^^
-If true, marks this field as a counter. The counter direction is inferred based
-based on which properties are assigned. By default, an up-counter is implemented.
-If any of the properties associated with an up-counter are used, then up-counting
-capabilities will be implemented. The same is true for down-counters and up/down
-counters.
-
-Unless alternate control signals are specified, the existence of input signals
-``hwif_in..incr`` and ``hwif_in..decr`` will be inferred depending on the type
-of counter described.
-
-
-incr
-^^^^
-Assign a reference to an alternate control signal to increment the counter.
-If assigned, the inferred ``hwif_in..incr`` input will not be generated.
-
-incrsaturate/saturate
-^^^^^^^^^^^^^^^^^^^^^
-If assigned, indicates that the counter will saturate instead of wrapping.
-If an alternate saturation point is specified, the counter value will be
-adjusted so that it does not exceed that limit, even after non-increment actions.
-
-boolean
-    If true, saturation point is at the counter's maximum count value. (2^width - 1)
-
-integer
-    Specify a static saturation value.
-
-reference
-    Specify a dynamic saturation value.
-
-
-incrthreshold/threshold
-^^^^^^^^^^^^^^^^^^^^^^^
-If assigned, infers a ``hwif_out..incrthreshold`` output signal. This signal is
-asserted if the counter value is greater or equal to the threshold.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                     "wave": "p......"},
-            {"name": "hwif_in..incr",           "wave": "01...0."},
-            {"name": "<counter>",               "wave": "=.=3==..", "data": [4,5,6,7,8,9]},
-            {"name": "hwif_out..incrthreshold", "wave": "0..1...."}
-        ],
-        "foot": {
-            "text": "Example where incrthreshold = 6"
-        }
-    }
-
-
-boolean
-    If true, threshold is the counter's maximum count value. (2^width - 1)
-
-integer
-    Specify a static threshold value.
-
-reference
-    Specify a dynamic threshold value.
-
-
-incrvalue
-^^^^^^^^^
-Override the counter's increment step size.
-
-integer
-    Specify a static increment step size.
-
-reference
-    Reference a component that controls the step size.
-
-incrwidth
-^^^^^^^^^
-If assigned, infers an input signal ``hwif_in..incrvalue``. The value of this
-property defines the signal's width.
-
-
-overflow
-^^^^^^^^
-If true, infers an output signal ``hwif_out..overflow`` that is asserted when
-the counter is about to wrap.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                "wave": "p......."},
-            {"name": "hwif_in..incr",      "wave": "0101010."},
-            {"name": "<counter>",          "wave": "=.=.=.=.", "data": [14,15,0,1]},
-            {"name": "hwif_out..overflow", "wave": "0..10..."}
-        ],
-        "foot": {
-            "text": "A 4-bit counter overflowing"
-        }
-    }
-
-
-decr
-^^^^
-Assign a reference to an alternate control signal to decrement the counter.
-If assigned, the inferred ``hwif_in..decr`` input will not be generated.
-
-
-decrsaturate
-^^^^^^^^^^^^
-If assigned, indicates that the counter will saturate instead of wrapping.
-If an alternate saturation point is specified, the counter value will be
-adjusted so that it does not exceed that limit, even after non-decrement actions.
-
-boolean
-    If true, saturation point is when the counter reaches 0.
-
-integer
-    Specify a static saturation value.
-
-reference
-    Specify a dynamic saturation value.
-
-
-decrthreshold
-^^^^^^^^^^^^^
-If assigned, infers a ``hwif_out..decrthreshold`` output signal. This signal is
-asserted if the counter value is less than or equal to the threshold.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                     "wave": "p......"},
-            {"name": "hwif_in..decr",           "wave": "01...0."},
-            {"name": "<counter>",               "wave": "=.=3==.", "data": [9,8,7,6,5,4]},
-            {"name": "hwif_out..decrthreshold", "wave": "0..1..."}
-        ],
-        "foot": {
-            "text": "Example where incrthreshold = 7"
-        }
-    }
-
-
-boolean
-    If true, threshold is 0.
-
-integer
-    Specify a static threshold value.
-
-reference
-    Specify a dynamic threshold value.
-
-
-decrvalue
-^^^^^^^^^
-Override the counter's decrement step size.
-
-integer
-    Specify a static step size.
-
-reference
-    Reference to a component that controls the step size.
-
-
-decrwidth
-^^^^^^^^^
-If assigned, infers an input signal ``hwif_in..decrvalue``. The value of this
-property defines the signal's width.
-
-
-underflow
-^^^^^^^^^
-If true, infers an output signal ``hwif_out..underflow`` that is asserted when
-the counter is about to wrap.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                 "wave": "p......."},
-            {"name": "hwif_in..decr",       "wave": "0101010."},
-            {"name": "<counter>",           "wave": "=.=.=.=.", "data": [1,0,15,14]},
-            {"name": "hwif_out..underflow", "wave": "0..10..."}
-        ],
-        "foot": {
-            "text": "A 4-bit counter underflowing"
-        }
-    }
-
---------------------------------------------------------------------------------
-
-Interrupt Properties
---------------------
-
-intr
-^^^^
-
-If set, this field becomes an interrupt field.
-The enclosing register infers an output signal ``hwif_out..intr`` which denotes
-that an interrupt is active. This is an or-reduction of all interrupt fields
-after applying the appropriate ``enable`` or ``mask`` to the field value.
-
-level (default)
-    Interrupt is level-sensitive. If a bit on the field's ``hwif_in..next`` input
-    is '1', it will trigger an interrupt event.
-
-posedge
-    If a bit on the field's ``hwif_in..next`` input transitions from '0' to '1',
-    it will trigger an interrupt event. This transition shall still be synchronous
-    to the register block's clock.
-
-negedge
-    If a bit on the field's ``hwif_in..next`` input transitions from '1' to '0',
-    it will trigger an interrupt event. This transition shall still be synchronous
-    to the register block's clock.
-
-bothedge
-    If a bit on the field's ``hwif_in..next`` input transitions from '0' to '1' or '1' to '0',
-    it will trigger an interrupt event. This transition shall still be synchronous
-    to the register block's clock.
-
-nonsticky
-    Interrupt event is not sticky.
-
-
-enable
-^^^^^^
-Reference to a field or signal that, if set to 1, define which bits in the field
-are used to assert an interrupt.
-
-
-mask
-^^^^
-Reference to a field or signal that, if set to 1, define which bits in the field
-are *not* used to assert an interrupt.
-
-
-haltenable
-^^^^^^^^^^
-Reference to a field or signal that, if set to 1, define which bits in the field
-are used to assert the halt output.
-
-If this property is set, the enclosing register will infer a ``hwif_out..halt`` output.
-
-
-haltmask
-^^^^^^^^
-Reference to a field or signal that, if set to 1, define which bits in the field
-are *not* used to assert the halt output.
-
-If this property is set, the enclosing register will infer a ``hwif_out..halt`` output.
-
-
-stickybit
-^^^^^^^^^
-When an interrupt trigger occurs, a stickybit field will set the corresponding
-bit to '1' and hold it until it is cleared by a software access.
-
-The interrupt trigger depends on the interrupt type. By default, interrupts are
-level-sensitive, but the interrupt modifiers allow for edge-sensitive triggers as
-well.
-
-The waveform below demonstrates a level-sensitive interrupt:
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                 "wave": "p....."},
-            {"name": "hwif_in..next",       "wave": "010..."},
-            {"name": "<field value>",       "wave": "0.1..."}
-        ]
-    }
-
-
-sticky
-^^^^^^
-Unlike ``stickybit`` fields, a sticky field will latch an entire value. The
-value is latched as soon as ``hwif_in..next`` is nonzero, and is held until the
-field contents are cleared back to 0 by a software access.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",                 "wave": "p....."},
-            {"name": "hwif_in..next",       "wave": "23.22.", "data": [0,10,20,30]},
-            {"name": "<field value>",       "wave": "2.3...", "data": [0, 10]}
-        ]
-    }
-
-
---------------------------------------------------------------------------------
-
-Misc
-----
-
-encode
-^^^^^^
-If assigned a user-defined enumeration, the resulting package file will include
-its definition. Due to limitations from type-strictness rules in SystemVerilog,
-the field will remain as a ``logic`` datatype.
-
-
-next
-^^^^
-If assigned, replaces the inferred ``hwif_in..next`` input with an explicit reference.
-
-
-paritycheck
-^^^^^^^^^^^
-If set, enables parity checking for this field.
-
-Adds a ``parity_error`` output signal to the module.
-
-.. note::
-
-    If this field does not implement storage, the ``partycheck`` property is ignored.
-
-
-
-precedence
-^^^^^^^^^^
-Control whether hardware or software has precedence when field value update
-contention occurs. Software has precedence by default.
-
-reset
-^^^^^
-Control the reset value of the field's storage element.
-If not specified, the field will not be reset.
-
-integer
-    Static reset value
-
-reference
-    Reference to a dynamic reset value.
-
-resetsignal
-^^^^^^^^^^^
-Provide an alternate reset trigger for this field.

docs/props/reg.rst

@@ -1,14 +0,0 @@
-Register Properties
-===================
-
-.. note:: Any properties not explicitly listed here are either implicitly
-    supported, or are not relevant to the busdecoder exporter and are ignored.
-
-accesswidth
------------
-Control the software access width. The register block's CPUIF bus width is
-determined by the maximum accesswidth encountered.
-
-regwidth
---------
-Control the bit-width of the register.

docs/props/rhs_props.rst

@@ -1,182 +0,0 @@
-RHS Property References
-=======================
-
-SystemRDL allows some properties to be referenced in the righthand-side of
-property assignment expressions:
-
-    .. code-block:: systemrdl
-
-            some_property = my_reg.my_field -> some_property;
-
-The official SystemRDL spec refers to these as "Ref targets" in Table G1, but
-unfortunately does not describe their semantics in much detail.
-
-The text below describes the interpretations used for this exporter.
-
---------------------------------------------------------------------------------
-
-Field
------
-
-field -> swacc
-^^^^^^^^^^^^^^
-Single-cycle strobe that indicates the field is being accessed by software
-(read or write).
-
-
-field -> swmod
-^^^^^^^^^^^^^^^
-Single-cycle strobe that indicates the field is being modified during a software
-access operation.
-
-
-field -> swwe/swwel
-^^^^^^^^^^^^^^^^^^^
-Represents the signal that controls the field's swwe/swwel behavior.
-
-
-field -> anded/ored/xored
-^^^^^^^^^^^^^^^^^^^^^^^^^
-Represents the current and/or/xor reduction of the field's value.
-
-
-field -> hwclr/hwset
-^^^^^^^^^^^^^^^^^^^^
-|EX|
-
-Represents the signal that controls the field's hwclr/hwset behavior.
-
-
-field -> hwenable/hwmask
-^^^^^^^^^^^^^^^^^^^^^^^^
-Represents the signal that controls the field's hwenable/hwmask behavior.
-
-field -> we/wel
-^^^^^^^^^^^^^^^
-Represents the signal that controls the field's we/wel behavior.
-
-field -> next
-^^^^^^^^^^^^^
-|EX|
-
-field -> reset
-^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-field -> resetsignal
-^^^^^^^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
---------------------------------------------------------------------------------
-
-Field Counter Properties
-------------------------
-
-field -> incr
-^^^^^^^^^^^^^
-Represents the signal that controls the field's counter increment control.
-
-
-field -> incrsaturate/saturate
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-Represents the internal 1-bit event signal that indicates whether the counter is saturated
-at its saturation value.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",            "wave": "p......"},
-            {"name": "hwif_in..decr",  "wave": "0101010"},
-            {"name": "<counter>",      "wave": "=.=....", "data": [1,0]},
-            {"name": "<decrsaturate>", "wave": "0.1...."}
-        ],
-        "foot": {
-            "text": "A 4-bit counter saturating"
-        }
-    }
-
-
-field -> incrthreshold/threshold
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-Represents the 1-bit event signal that indicates whether the counter has met or
-exceeded its incrthreshold.
-
-field -> incrvalue
-^^^^^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-field -> overflow
-^^^^^^^^^^^^^^^^^
-Represents the event signal that is asserted when the counter is about to wrap.
-
-field -> decr
-^^^^^^^^^^^^^
-Represents the signal that controls the field's counter decrement control.
-
-field -> decrsaturate
-^^^^^^^^^^^^^^^^^^^^^
-Represents the internal 1-bit event signal that indicates whether the counter is saturated
-at its saturation value.
-
-.. wavedrom::
-
-    {
-        "signal": [
-            {"name": "clk",            "wave": "p......"},
-            {"name": "hwif_in..incr",  "wave": "0101010"},
-            {"name": "<counter>",      "wave": "=.=....", "data": [14,15]},
-            {"name": "<incrsaturate>", "wave": "0.1...."}
-        ],
-        "foot": {
-            "text": "A 4-bit counter saturating"
-        }
-    }
-
-field -> decrthreshold
-^^^^^^^^^^^^^^^^^^^^^^
-Represents the 1-bit event signal that indicates whether the counter has met or
-exceeded its incrthreshold.
-
-field -> decrvalue
-^^^^^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-field -> underflow
-^^^^^^^^^^^^^^^^^^
-Represents the event signal that is asserted when the counter is about to wrap.
-
---------------------------------------------------------------------------------
-
-Field Interrupt Properties
---------------------------
-
-field -> enable
-^^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-field -> mask
-^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-field -> haltenable
-^^^^^^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-field -> haltmask
-^^^^^^^^^^^^^^^^^
-Represents the value that was assigned to this property.
-
-
---------------------------------------------------------------------------------
-
-Register
---------
-
-reg -> intr
-^^^^^^^^^^^
-References the register's ``hwif_out..intr`` signal.
-
-reg -> halt
-^^^^^^^^^^^
-References the register's ``hwif_out..halt`` signal.

docs/props/signal.rst

@@ -1,28 +0,0 @@
-Signal Properties
-=================
-
-.. note:: Any properties not explicitly listed here are either implicitly
-    supported, or are not relevant to the busdecoder exporter and are ignored.
-
-
-activehigh/activelow
---------------------
-Only relevant for signals used as resets. Defines the reset signal's polarity.
-
-
-sync/async
-----------
-Only supported for signals used as resets to infer edge-sensitive reset.
-Ignored in all other contexts.
-
-
-cpuif_reset
------------
-Specify that this signal shall be used as alternate reset signal for the CPU
-interface for this busdecoder.
-
-
-field_reset
------------
-Specify that this signal is used as an alternate reset signal for all fields
-instantiated in sub-hierarchies relative to this signal.

docs/rdl_features/external.rst

@@ -1,155 +0,0 @@
-External Components
-===================
-SystemRDL allows some component instances to be defined as "external" elements
-of an address space definition. In the context of this busdecoder generator,
-the implementation of an external component is left up to the designer. When
-generating the RTL for a busdecoder, the implementations of external components
-are omitted and instead a user-interface is presented on the
-``hwif_in``/``hwif_out`` i/o structs.
-
-External component signals on the hardware interface closely follow the semantics
-of the :ref:`cpuif_protocol`.
-
-
-Things you should know
-----------------------
-
-* By default external ``hwif_out`` signals are driven combinationally. An
-  optional output retiming stage can be enabled if needed.
-* Due to the uncertain access latency of external components, the busdecoder will
-  only issue one outstanding transaction to an external component at a time.
-  This is enforced even if the CPUIF is capable of pipelined accesses such as
-  AXI4-Lite.
-
-
-External Registers
-------------------
-External registers can be useful if it is necessary to implement a register that
-cannot easily be expressed using SystemRDL semantics. This could be a unique
-access policy, or FIFO-like push/pop registers.
-
-External registers are annotated as such by using the ``external`` keyword:
-
-.. code-block:: systemrdl
-
-    // An internal register
-    my_reg int_reg;
-
-    // An external register
-    external my_reg ext_reg;
-
-Request
-^^^^^^^
-hwif_out..req
-    When asserted, a read or write transfer will be initiated.
-    Qualifies all other request signals.
-
-    If the register is wide (``regwidth`` > ``accesswidth``), then the
-    ``hwif_out..req`` will consist of multiple bits, representing the access
-    strobe for each sub-word of the register.
-
-    If the register does not contain any readable fields, this strobe will be
-    suppressed for read operations.
-
-    If the register does not contain any writable readable fields, this strobe
-    will be suppressed for write operations.
-
-hwif_out..req_is_wr
-    If ``1``, denotes that the current transfer is a write. Otherwise transfer is
-    a read.
-
-hwif_out..wr_data
-    Data to be written for the write transfer. This signal is ignored for read
-    transfers.
-
-    The bit-width of this signal always matches the CPUIF's bus width,
-    regardless of the regwidth.
-
-    If the register does not contain any writable fields, this signal is omitted.
-
-hwif_out..wr_biten
-    Active-high bit-level write-enable strobes.
-    Only asserted bit positions will change the register value during a write
-    transfer.
-
-    If the register does not contain any writable fields, this signal is omitted.
-
-
-Read Response
-^^^^^^^^^^^^^
-hwif_in..rd_ack
-    Single-cycle strobe indicating a read transfer has completed.
-    Qualifies all other read response signals.
-
-    If the transfer is always completed in the same cycle, it is acceptable to
-    tie this signal to ``hwif_out..req && !hwif_out..req_is_wr``.
-
-    If the register does not contain any readable fields, this signal is omitted.
-
-hwif_in..rd_data
-    Read response data.
-
-    If the register does not contain any readable fields, this signal is omitted.
-
-Write Response
-^^^^^^^^^^^^^^
-hwif_in..wr_ack
-    Single-cycle strobe indicating a write transfer has completed.
-
-    If the transfer is always completed in the same cycle, it is acceptable to
-    tie this signal to ``hwif_out..req && hwif_out..req_is_wr``.
-
-    If the register does not contain any writable fields, this signal is omitted.
-
-
-
-External Blocks
----------------
-Broader external address regions can be represented by external block-like
-components such as ``addrmap``, ``regfile`` or ``mem`` elements.
-
-To ensure address decoding for external blocks is simple (only requires simple bit-pruning),
-blocks that are external to an exported busdecoder shall be aligned to their size.
-
-Request
-^^^^^^^
-hwif_out..req
-    When asserted, a read or write transfer will be initiated.
-    Qualifies all other request signals.
-
-hwif_out..addr
-    Byte-address of the transfer.
-
-    Address is always relative to the block's local addressing. i.e: The first
-    byte within an external block is represented as ``hwif_out..addr`` == 0,
-    regardless of the absolute address of the block.
-
-hwif_out..req_is_wr
-    If ``1``, denotes that the current transfer is a write. Otherwise transfer is
-    a read.
-
-hwif_out..wr_data
-    Data to be written for the write transfer. This signal is ignored for read
-    transfers.
-
-    The bit-width of this signal always matches the CPUIF's bus width,
-    regardless of the contents of the block.
-
-hwif_out..wr_biten
-    Active-high bit-level write-enable strobes.
-    Only asserted bit positions will change the register value during a write
-    transfer.
-
-Read Response
-^^^^^^^^^^^^^
-hwif_in..rd_ack
-    Single-cycle strobe indicating a read transfer has completed.
-    Qualifies all other read response signals.
-
-hwif_in..rd_data
-    Read response data.
-
-Write Response
-^^^^^^^^^^^^^^
-hwif_in..wr_ack
-    Single-cycle strobe indicating a write transfer has completed.

docs/requirements.txt

@@ -1,3 +1,2 @@
 pygments-systemrdl
-sphinxcontrib-wavedrom
 sphinx-book-theme

docs/udps/intro.rst

@@ -1,79 +0,0 @@
-Introduction
-============
-
-Although the official SystemRDL spec defines numerous properties that allow you
-to define complex register map structures, sometimes they are not enough to
-accurately describe a necessary feature. Fortunately the SystemRDL spec allows
-the language to be extended using "User Defined Properties" (UDPs).
-
-Current UDP Support
--------------------
-
-**Note:** PeakRDL-BusDecoder currently does not implement any User Defined Properties.
-The focus of this tool is on bus decoding and address space routing rather than 
-field-level or register-level behavioral extensions.
-
-If you need UDPs for field-level behaviors (such as buffering, signedness, or 
-fixed-point representations), consider using `PeakRDL-regblock <https://github.com/SystemRDL/PeakRDL-regblock>`_,
-which is designed for comprehensive register block generation with extensive UDP support.
-
-Extending with Custom UDPs
----------------------------
-
-If your bus decoder design requires custom User Defined Properties, you can extend
-PeakRDL-BusDecoder by:
-
-1. **Define your UDP in SystemRDL**
-
-   Create a ``.rdl`` file that defines your custom properties:
-
-   .. code-block:: systemrdl
-
-      property my_custom_prop {
-          component = addrmap;
-          type = boolean;
-      };
-
-2. **Implement the UDP in Python**
-
-   Create a Python UDP definition class in your project:
-
-   .. code-block:: python
-
-      from systemrdl.udp import UDPDefinition
-
-      class MyCustomUDP(UDPDefinition):
-          name = "my_custom_prop"
-          valid_components = {"addrmap"}
-          valid_type = bool
-          default = False
-
-3. **Register the UDP with the compiler**
-
-   When using PeakRDL-BusDecoder programmatically, register your UDP:
-
-   .. code-block:: python
-
-      from systemrdl import RDLCompiler
-      from peakrdl_busdecoder import BusDecoderExporter
-
-      rdlc = RDLCompiler()
-      rdlc.register_udp(MyCustomUDP)
-      
-      # Compile your RDL files
-      rdlc.compile_file("my_udp_defs.rdl")
-      rdlc.compile_file("my_design.rdl")
-      
-      root = rdlc.elaborate()
-      
-      # Export
-      exporter = BusDecoderExporter()
-      exporter.export(root, "output/")
-
-4. **Access UDP values in your design**
-
-   UDP values can be accessed from nodes in the SystemRDL tree and used to
-   customize the generated bus decoder logic as needed.
-
-For more information on creating User Defined Properties, see the 
-`SystemRDL Compiler documentation <https://systemrdl-compiler.readthedocs.io/en/stable/model_structure.html#user-defined-properties>`_.

hdl-src/apb3_intf.sv

@@ -2,6 +2,10 @@ interface apb3_intf #(
     parameter DATA_WIDTH = 32,
     parameter ADDR_WIDTH = 32
 );
+    // Clocking
+    logic PCLK;
+    logic PRESETn;
+
     // Command
     logic PSEL;
     logic PENABLE;
@@ -15,6 +19,9 @@ interface apb3_intf #(
     logic PSLVERR;
 
     modport master (
+        input PCLK,
+        input PRESETn,
+
         output PSEL,
         output PENABLE,
         output PWRITE,
@@ -27,6 +34,9 @@ interface apb3_intf #(
     );
 
     modport slave (
+        input PCLK,
+        input PRESETn,
+
         input PSEL,
         input PENABLE,
         input PWRITE,

hdl-src/apb4_intf.sv

@@ -2,6 +2,10 @@ interface apb4_intf #(
     parameter DATA_WIDTH = 32,
     parameter ADDR_WIDTH = 32
 );
+    // Clocking
+    logic PCLK;
+    logic PRESETn;
+
     // Command
     logic PSEL;
     logic PENABLE;
@@ -17,6 +21,9 @@ interface apb4_intf #(
     logic PSLVERR;
 
     modport master (
+        input PCLK,
+        input PRESETn,
+
         output PSEL,
         output PENABLE,
         output PWRITE,
@@ -31,6 +38,9 @@ interface apb4_intf #(
     );
 
     modport slave (
+        input PCLK,
+        input PRESETn,
+
         input PSEL,
         input PENABLE,
         input PWRITE,

hdl-src/axi4lite_intf.sv

@@ -2,6 +2,9 @@ interface axi4lite_intf #(
     parameter DATA_WIDTH = 32,
     parameter ADDR_WIDTH = 32
 );
+    logic ACLK;
+    logic ARESETn;
+
     logic AWREADY;
     logic AWVALID;
     logic [ADDR_WIDTH-1:0] AWADDR;
@@ -27,6 +30,9 @@ interface axi4lite_intf #(
     logic [1:0] RRESP;
 
     modport master (
+        input ACLK,
+        input ARESETn,
+
         input AWREADY,
         output AWVALID,
         output AWADDR,
@@ -53,15 +59,18 @@ interface axi4lite_intf #(
     );
 
     modport slave (
+        input ACLK,
+        input ARESETn,
+
         output AWREADY,
-        // input AWVALID,
-        // input AWADDR,
+        input AWVALID,
+        input AWADDR,
         input AWPROT,
 
         output WREADY,
-        // input WVALID,
-        // input WDATA,
-        // input WSTRB,
+        input WVALID,
+        input WDATA,
+        input WSTRB,
 
         input BREADY,
         output BVALID,
@@ -73,8 +82,8 @@ interface axi4lite_intf #(
         input ARPROT,
 
         input RREADY,
-        // output RVALID,
-        // output RDATA,
-        // output RRESP
+        output RVALID,
+        output RDATA,
+        output RRESP
     );
 endinterface

pyproject.toml

@@ -4,11 +4,14 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "peakrdl-busdecoder"
-version = "0.1.0"
+version = "0.6.7"
 requires-python = ">=3.10"
-dependencies = ["jinja2>=3.1.6", "systemrdl-compiler~=1.30.1"]
+dependencies = [
+    "jinja2~=3.1",
+    "systemrdl-compiler~=1.30",
+]
 
-authors = [{ name = "Alex Mykyta" }]
+authors = [{ name = "Arnav Sacheti" }]
 description = "Generate a SystemVerilog bus decoder from SystemRDL for splitting CPU interfaces to multiple sub-address spaces"
 readme = "README.md"
 license = { text = "LGPLv3" }
@@ -52,20 +55,21 @@ Documentation = "https://peakrdl-busdecoder.readthedocs.io/"
 docs = [
     "pygments-systemrdl>=1.3.0",
     "sphinx-book-theme>=1.1.4",
-    "sphinxcontrib-wavedrom>=3.0.4",
 ]
 test = [
     "parameterized>=0.9.0",
     "pytest>=7.4.4",
     "pytest-cov>=4.1.0",
     "pytest-xdist>=3.5.0",
+    "cocotb>=1.8.0",
+    "cocotb-bus>=0.2.1",
 ]
-tools = ["pyrefly>=0.37.0", "ruff>=0.14.0"]
+tools = ["ty>=0.0.7", "ruff>=0.14.0"]
 
 [project.entry-points."peakrdl.exporters"]
 busdecoder = "peakrdl_busdecoder.__peakrdl__:Exporter"
 
-
+# ---------------------- RUFF ----------------------
 [tool.ruff]
 line-length = 110
 target-version = "py310"
@@ -95,12 +99,18 @@ ignore = [
 quote-style = "double"
 indent-style = "space"
 
-# ---------------------- PYREFLY ----------------------
-[tool.pyrefly]
+# ---------------------- TY ----------------------
+[tool.ty.environment]
 python-version = "3.10"
 
-# Default behavior: check bodies of untyped defs & infer return types.
-untyped-def-behavior = "check-and-infer-return-type"
+[tool.ty.src]
+include = ["src"]
 
-project-includes = ["**/*"]
-project-excludes = ["**/__pycache__", "**/*venv/**/*"]
+# ---------------------- PYTEST ----------------------
+[tool.pytest.ini_options]
+python_files = ["test_*.py", "*_test.py"]
+markers = [
+    "simulation: marks tests as requiring cocotb simulation (deselect with '-m \"not simulation\"')",
+    "verilator: marks tests as requiring verilator simulator (deselect with '-m \"not verilator\"')",
+]
+filterwarnings = ["error", "ignore::UserWarning"]

src/peakrdl_busdecoder/__peakrdl__.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import functools
 from typing import TYPE_CHECKING, Any
 
@@ -5,7 +7,7 @@ from peakrdl.config import schema
 from peakrdl.plugins.entry_points import get_entry_points
 from peakrdl.plugins.exporter import ExporterSubcommandPlugin
 
-from .cpuif import BaseCpuif, apb3, apb4, axi4lite
+from .cpuif import BaseCpuif, apb3, apb4, axi4lite, taxi_apb
 from .exporter import BusDecoderExporter
 from .udps import ALL_UDPS
 
@@ -24,6 +26,7 @@ def get_cpuifs(config: list[tuple[str, Any]]) -> dict[str, type[BaseCpuif]]:
         "apb3-flat": apb3.APB3CpuifFlat,
         "apb4": apb4.APB4Cpuif,
         "apb4-flat": apb4.APB4CpuifFlat,
+        "taxi-apb": taxi_apb.TaxiAPBCpuif,
         "axi4-lite": axi4lite.AXI4LiteCpuif,
         "axi4-lite-flat": axi4lite.AXI4LiteCpuifFlat,
     }
@@ -69,7 +72,7 @@ class Exporter(ExporterSubcommandPlugin):
     def get_cpuifs(self) -> dict[str, type[BaseCpuif]]:
         return get_cpuifs(map(tuple, self.cfg["cpuifs"].items()))
 
-    def add_exporter_arguments(self, arg_group: "argparse.ArgumentParser") -> None:  # type: ignore
+    def add_exporter_arguments(self, arg_group: argparse._ActionsContainer) -> None:
         cpuifs = self.get_cpuifs()
 
         arg_group.add_argument(
@@ -111,7 +114,18 @@ class Exporter(ExporterSubcommandPlugin):
             """,
         )
 
-    def do_export(self, top_node: "AddrmapNode", options: "argparse.Namespace") -> None:
+        arg_group.add_argument(
+            "--max-decode-depth",
+            type=int,
+            default=1,
+            help="""Maximum depth for address decoder to descend into nested
+            addressable components. Value of 0 decodes all levels (infinite depth).
+            Value of 1 decodes only top-level children. Value of 2 decodes top-level
+            and one level deeper, etc. Default is 1.
+            """,
+        )
+
+    def do_export(self, top_node: AddrmapNode, options: argparse.Namespace) -> None:
         cpuifs = self.get_cpuifs()
 
         x = BusDecoderExporter()
@@ -123,4 +137,5 @@ class Exporter(ExporterSubcommandPlugin):
             package_name=options.package_name,
             address_width=options.addr_width,
             cpuif_unroll=options.unroll,
+            max_decode_depth=options.max_decode_depth,
         )

src/peakrdl_busdecoder/body/if_body.py

@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from textwrap import indent
 from types import EllipsisType
 
@@ -50,7 +48,7 @@ class IfBody(Body):
 
     # --- Context manager for a branch ---
     class _BranchCtx:
-        def __init__(self, outer: IfBody, condition: SupportsStr | None) -> None:
+        def __init__(self, outer: "IfBody", condition: SupportsStr | None) -> None:
             self._outer = outer
             # route through __getitem__ to reuse validation logic
             self._body = outer[Ellipsis if condition is None else condition]
@@ -66,7 +64,7 @@ class IfBody(Body):
         ) -> bool:
             return False
 
-    def cm(self, condition: SupportsStr | None) -> IfBody._BranchCtx:
+    def cm(self, condition: SupportsStr | None) -> "IfBody._BranchCtx":
         """Use with: with ifb.cm('cond') as b: ...  ; use None for else."""
         return IfBody._BranchCtx(self, condition)
 

src/peakrdl_busdecoder/cpuif/apb3/apb3_cpuif.py

@@ -1,49 +1,39 @@
-from typing import overload
+from collections import deque
+from typing import TYPE_CHECKING, overload
 
 from systemrdl.node import AddressableNode
 
 from ...utils import get_indexed_path
 from ..base_cpuif import BaseCpuif
+from .apb3_interface import APB3SVInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
 
 
 class APB3Cpuif(BaseCpuif):
     template_path = "apb3_tmpl.sv"
-    is_interface = True
 
-    def _port_declaration(self, child: AddressableNode) -> str:
-        base = f"apb3_intf.master m_apb_{child.inst_name}"
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = APB3SVInterface(self)
 
-        # When unrolled, current_idx is set - append it to the name
-        if child.current_idx is not None:
-            base = f"{base}_{'_'.join(map(str, child.current_idx))}"
-
-        # Only add array dimensions if this should be treated as an array
-        if self.check_is_array(child):
-            assert child.array_dimensions is not None
-            return f"{base} {''.join(f'[{dim}]' for dim in child.array_dimensions)}"
-
-        return base
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
 
     @property
     def port_declaration(self) -> str:
-        slave_ports: list[str] = ["apb3_intf.slave s_apb"]
-        master_ports: list[str] = list(map(self._port_declaration, self.addressable_children))
-
-        return ",\n".join(slave_ports + master_ports)
+        return self._interface.get_port_declaration("s_apb", "m_apb_")
 
     @overload
     def signal(self, signal: str, node: None = None, indexer: None = None) -> str: ...
     @overload
     def signal(self, signal: str, node: AddressableNode, indexer: str) -> str: ...
     def signal(self, signal: str, node: AddressableNode | None = None, indexer: str | None = None) -> str:
-        if node is None or indexer is None:
-            # Node is none, so this is a slave signal
-            return f"s_apb.{signal}"
+        return self._interface.signal(signal, node, indexer)
 
-        # Master signal
-        return f"m_apb_{get_indexed_path(node.parent, node, indexer, skip_kw_filter=True)}.{signal}"
-
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         fanout: dict[str, str] = {}
         fanout[self.signal("PSEL", node, "gi")] = (
             f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
@@ -55,24 +45,60 @@ class APB3Cpuif(BaseCpuif):
         fanout[self.signal("PADDR", node, "gi")] = self.signal("PADDR")
         fanout[self.signal("PWDATA", node, "gi")] = "cpuif_wr_data"
 
-        return "\n".join(map(lambda kv: f"assign {kv[0]} = {kv[1]};", fanout.items()))
+        return "\n".join(f"assign {kv[0]} = {kv[1]};" for kv in fanout.items())
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_wr_ack"] = "'0"
+            fanin["cpuif_wr_err"] = "'0"
+            if error:
+                fanin["cpuif_wr_ack"] = "'1"
+                fanin["cpuif_wr_err"] = "cpuif_wr_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_wr_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_wr_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+            else:
+                fanin["cpuif_wr_ack"] = self.signal("PREADY", node, "i")
+                fanin["cpuif_wr_err"] = self.signal("PSLVERR", node, "i")
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         fanin: dict[str, str] = {}
         if node is None:
             fanin["cpuif_rd_ack"] = "'0"
             fanin["cpuif_rd_err"] = "'0"
+            fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_rd_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_rd_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+                fanin["cpuif_rd_data"] = f"{node.inst_name}_fanin_data{array_idx}"
             else:
                 fanin["cpuif_rd_ack"] = self.signal("PREADY", node, "i")
                 fanin["cpuif_rd_err"] = self.signal("PSLVERR", node, "i")
-
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
-
-    def readback(self, node: AddressableNode | None = None) -> str:
-        fanin: dict[str, str] = {}
-        if node is None:
-            fanin["cpuif_rd_data"] = "'0"
-        else:
                 fanin["cpuif_rd_data"] = self.signal("PRDATA", node, "i")
 
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())
+
+    def fanin_intermediate_assignments(
+        self, node: AddressableNode, inst_name: str, array_idx: str, master_prefix: str, indexed_path: str
+    ) -> list[str]:
+        """Generate intermediate signal assignments for APB3 interface arrays."""
+        return [
+            f"assign {inst_name}_fanin_ready{array_idx} = {master_prefix}{indexed_path}.PREADY;",
+            f"assign {inst_name}_fanin_err{array_idx} = {master_prefix}{indexed_path}.PSLVERR;",
+            f"assign {inst_name}_fanin_data{array_idx} = {master_prefix}{indexed_path}.PRDATA;",
+        ]

src/peakrdl_busdecoder/cpuif/apb3/apb3_cpuif_flat.py

@@ -1,46 +1,31 @@
+from collections import deque
+from typing import TYPE_CHECKING
+
 from systemrdl.node import AddressableNode
 
-from ...utils import get_indexed_path
+from ...sv_int import SVInt
+from ...utils import clog2, get_indexed_path
 from ..base_cpuif import BaseCpuif
+from .apb3_interface import APB3FlatInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
 
 
 class APB3CpuifFlat(BaseCpuif):
     template_path = "apb3_tmpl.sv"
-    is_interface = False
 
-    def _port_declaration(self, child: AddressableNode) -> list[str]:
-        return [
-            f"input logic {self.signal('PCLK', child)}",
-            f"input logic {self.signal('PRESETn', child)}",
-            f"input logic {self.signal('PSELx', child)}",
-            f"input logic {self.signal('PENABLE', child)}",
-            f"input logic {self.signal('PWRITE', child)}",
-            f"input logic [{self.addr_width - 1}:0] {self.signal('PADDR', child)}",
-            f"input logic [{self.data_width - 1}:0] {self.signal('PWDATA', child)}",
-            f"output logic [{self.data_width - 1}:0] {self.signal('PRDATA', child)}",
-            f"output logic {self.signal('PREADY', child)}",
-            f"output logic {self.signal('PSLVERR', child)}",
-        ]
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = APB3FlatInterface(self)
+
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
 
     @property
     def port_declaration(self) -> str:
-        slave_ports: list[str] = [
-            f"input logic {self.signal('PCLK')}",
-            f"input logic {self.signal('PRESETn')}",
-            f"input logic {self.signal('PSELx')}",
-            f"input logic {self.signal('PENABLE')}",
-            f"input logic {self.signal('PWRITE')}",
-            f"input logic [{self.addr_width - 1}:0] {self.signal('PADDR')}",
-            f"input logic [{self.data_width - 1}:0] {self.signal('PWDATA')}",
-            f"output logic [{self.data_width - 1}:0] {self.signal('PRDATA')}",
-            f"output logic {self.signal('PREADY')}",
-            f"output logic {self.signal('PSLVERR')}",
-        ]
-        master_ports: list[str] = []
-        for child in self.addressable_children:
-            master_ports.extend(self._port_declaration(child))
-
-        return ",\n".join(slave_ports + master_ports)
+        return self._interface.get_port_declaration("s_apb_", "m_apb_")
 
     def signal(
         self,
@@ -48,53 +33,52 @@ class APB3CpuifFlat(BaseCpuif):
         node: AddressableNode | None = None,
         idx: str | int | None = None,
     ) -> str:
-        if node is None:
-            # Node is none, so this is a slave signal
-            return f"s_apb_{signal}"
+        return self._interface.signal(signal, node, idx)
 
-        # Master signal
-        base = f"m_apb_{node.inst_name}"
-        if not self.check_is_array(node):
-            # Not an array or an unrolled element
-            if node.current_idx is not None:
-                # This is a specific instance of an unrolled array
-                return f"{base}_{signal}_{'_'.join(map(str, node.current_idx))}"
-            return f"{base}_{signal}"
-        # Is an array
-        if idx is not None:
-            return f"{base}_{signal}[{idx}]"
-        return f"{base}_{signal}[N_{node.inst_name.upper()}S]"
-
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         fanout: dict[str, str] = {}
-        fanout[self.signal("PSELx", node)] = (
-            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'i')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'i')}"
-        )
-        fanout[self.signal("PENABLE", node)] = self.signal("PENABLE")
-        fanout[self.signal("PWRITE", node)] = (
-            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'i')}"
-        )
-        fanout[self.signal("PADDR", node)] = self.signal("PADDR")
-        fanout[self.signal("PWDATA", node)] = "cpuif_wr_data"
+        addr_comp = [f"{self.signal('PADDR')}"]
+        for i, stride in enumerate(array_stack):
+            addr_comp.append(f"(gi{i}*{SVInt(stride, self.addr_width)})")
 
-        return "\n".join(map(lambda kv: f"assign {kv[0]} = {kv[1]};", fanout.items()))
+        fanout[self.signal("PSEL", node, "gi")] = (
+            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
+        )
+        fanout[self.signal("PENABLE", node, "gi")] = self.signal("PENABLE")
+        fanout[self.signal("PWRITE", node, "gi")] = (
+            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
+        )
+        fanout[self.signal("PADDR", node, "gi")] = f"{{{'-'.join(addr_comp)}}}[{clog2(node.size) - 1}:0]"
+        fanout[self.signal("PWDATA", node, "gi")] = "cpuif_wr_data"
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+        return "\n".join(f"assign {kv[0]} = {kv[1]};" for kv in fanout.items())
+
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_wr_ack"] = "'0"
+            fanin["cpuif_wr_err"] = "'0"
+            if error:
+                fanin["cpuif_wr_ack"] = "'1"
+                fanin["cpuif_wr_err"] = "cpuif_wr_sel.cpuif_err"
+        else:
+            fanin["cpuif_wr_ack"] = self.signal("PREADY", node, "i")
+            fanin["cpuif_wr_err"] = self.signal("PSLVERR", node, "i")
+
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         fanin: dict[str, str] = {}
         if node is None:
             fanin["cpuif_rd_ack"] = "'0"
             fanin["cpuif_rd_err"] = "'0"
-        else:
-            fanin["cpuif_rd_ack"] = self.signal("PREADY", node)
-            fanin["cpuif_rd_err"] = self.signal("PSLVERR", node)
-
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
-
-    def readback(self, node: AddressableNode | None = None) -> str:
-        fanin: dict[str, str] = {}
-        if node is None:
             fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
         else:
-            fanin["cpuif_rd_data"] = self.signal("PRDATA", node)
+            fanin["cpuif_rd_ack"] = self.signal("PREADY", node, "i")
+            fanin["cpuif_rd_err"] = self.signal("PSLVERR", node, "i")
+            fanin["cpuif_rd_data"] = self.signal("PRDATA", node, "i")
 
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())

src/peakrdl_busdecoder/cpuif/apb3/apb3_interface.py

@@ -0,0 +1,57 @@
+"""APB3-specific interface implementations."""
+
+from systemrdl.node import AddressableNode
+
+from ...utils import clog2
+from ..interface import FlatInterface, SVInterface
+
+
+class APB3SVInterface(SVInterface):
+    """APB3 SystemVerilog interface."""
+
+    def get_interface_type(self) -> str:
+        return "apb3_intf"
+
+    def get_slave_name(self) -> str:
+        return "s_apb"
+
+    def get_master_prefix(self) -> str:
+        return "m_apb_"
+
+
+class APB3FlatInterface(FlatInterface):
+    """APB3 flat signal interface."""
+
+    def get_slave_prefix(self) -> str:
+        return "s_apb_"
+
+    def get_master_prefix(self) -> str:
+        return "m_apb_"
+
+    def _get_slave_port_declarations(self, slave_prefix: str) -> list[str]:
+        return [
+            f"input  logic {slave_prefix}PCLK",
+            f"input  logic {slave_prefix}PRESETn",
+            f"input  logic {slave_prefix}PSEL",
+            f"input  logic {slave_prefix}PENABLE",
+            f"input  logic {slave_prefix}PWRITE",
+            f"input  logic [{self.cpuif.addr_width - 1}:0] {slave_prefix}PADDR",
+            f"input  logic [{self.cpuif.data_width - 1}:0] {slave_prefix}PWDATA",
+            f"output logic [{self.cpuif.data_width - 1}:0] {slave_prefix}PRDATA",
+            f"output logic {slave_prefix}PREADY",
+            f"output logic {slave_prefix}PSLVERR",
+        ]
+
+    def _get_master_port_declarations(self, child: AddressableNode, master_prefix: str) -> list[str]:
+        return [
+            f"output logic {self.signal('PCLK', child)}",
+            f"output logic {self.signal('PRESETn', child)}",
+            f"output logic {self.signal('PSEL', child)}",
+            f"output logic {self.signal('PENABLE', child)}",
+            f"output logic {self.signal('PWRITE', child)}",
+            f"output logic [{clog2(child.size) - 1}:0] {self.signal('PADDR', child)}",
+            f"output logic [{self.cpuif.data_width - 1}:0] {self.signal('PWDATA', child)}",
+            f"input  logic [{self.cpuif.data_width - 1}:0] {self.signal('PRDATA', child)}",
+            f"input  logic {self.signal('PREADY', child)}",
+            f"input  logic {self.signal('PSLVERR', child)}",
+        ]

src/peakrdl_busdecoder/cpuif/apb3/apb3_tmpl.sv

@@ -19,13 +19,20 @@ assign cpuif_rd_addr = {{cpuif.signal("PADDR")}};
 assign cpuif_wr_data = {{cpuif.signal("PWDATA")}};
 
 assign {{cpuif.signal("PRDATA")}} = cpuif_rd_data;
-assign {{cpuif.signal("PREADY")}} = cpuif_rd_ack;
-assign {{cpuif.signal("PSLVERR")}} = cpuif_rd_err | cpuif_rd_sel.cpuif_err | cpuif_wr_sel.cpuif_err;
+assign {{cpuif.signal("PREADY")}} = cpuif_rd_ack | cpuif_wr_ack;
+assign {{cpuif.signal("PSLVERR")}} = cpuif_rd_err | cpuif_wr_err;
 
 //--------------------------------------------------------------------------
 // Fanout CPU Bus interface signals
 //--------------------------------------------------------------------------
 {{fanout|walk(cpuif=cpuif)}}
+{%- if cpuif.is_interface %}
+
+//--------------------------------------------------------------------------
+// Intermediate signals for interface array fanin
+//--------------------------------------------------------------------------
+{{fanin_intermediate|walk(cpuif=cpuif)}}
+{%- endif %}
 
 //--------------------------------------------------------------------------
 // Fanin CPU Bus interface signals

src/peakrdl_busdecoder/cpuif/apb4/apb4_cpuif.py

@@ -1,50 +1,40 @@
-from typing import overload
+from collections import deque
+from typing import TYPE_CHECKING, overload
 
 from systemrdl.node import AddressableNode
 
 from ...utils import get_indexed_path
 from ..base_cpuif import BaseCpuif
+from .apb4_interface import APB4SVInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
 
 
 class APB4Cpuif(BaseCpuif):
     template_path = "apb4_tmpl.sv"
-    is_interface = True
 
-    def _port_declaration(self, child: AddressableNode) -> str:
-        base = f"apb4_intf.master m_apb_{child.inst_name}"
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = APB4SVInterface(self)
 
-        # When unrolled, current_idx is set - append it to the name
-        if child.current_idx is not None:
-            base = f"{base}_{'_'.join(map(str, child.current_idx))}"
-
-        # Only add array dimensions if this should be treated as an array
-        if self.check_is_array(child):
-            assert child.array_dimensions is not None
-            return f"{base} {''.join(f'[{dim}]' for dim in child.array_dimensions)}"
-
-        return base
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
 
     @property
     def port_declaration(self) -> str:
         """Returns the port declaration for the APB4 interface."""
-        slave_ports: list[str] = ["apb4_intf.slave s_apb"]
-        master_ports: list[str] = list(map(self._port_declaration, self.addressable_children))
-
-        return ",\n".join(slave_ports + master_ports)
+        return self._interface.get_port_declaration("s_apb", "m_apb_")
 
     @overload
     def signal(self, signal: str, node: None = None, indexer: None = None) -> str: ...
     @overload
     def signal(self, signal: str, node: AddressableNode, indexer: str) -> str: ...
     def signal(self, signal: str, node: AddressableNode | None = None, indexer: str | None = None) -> str:
-        if node is None or indexer is None:
-            # Node is none, so this is a slave signal
-            return f"s_apb.{signal}"
+        return self._interface.signal(signal, node, indexer)
 
-        # Master signal
-        return f"m_apb_{get_indexed_path(node.parent, node, indexer, skip_kw_filter=True)}.{signal}"
-
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         fanout: dict[str, str] = {}
         fanout[self.signal("PSEL", node, "gi")] = (
             f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
@@ -58,24 +48,61 @@ class APB4Cpuif(BaseCpuif):
         fanout[self.signal("PWDATA", node, "gi")] = "cpuif_wr_data"
         fanout[self.signal("PSTRB", node, "gi")] = "cpuif_wr_byte_en"
 
-        return "\n".join(map(lambda kv: f"assign {kv[0]} = {kv[1]};", fanout.items()))
+        return "\n".join(f"assign {kv[0]} = {kv[1]};" for kv in fanout.items())
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_wr_ack"] = "'0"
+            fanin["cpuif_wr_err"] = "'0"
+            if error:
+                fanin["cpuif_wr_ack"] = "'1"
+                fanin["cpuif_wr_err"] = "cpuif_wr_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_wr_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_wr_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+            else:
+                fanin["cpuif_wr_ack"] = self.signal("PREADY", node, "i")
+                fanin["cpuif_wr_err"] = self.signal("PSLVERR", node, "i")
+
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         fanin: dict[str, str] = {}
         if node is None:
             fanin["cpuif_rd_ack"] = "'0"
             fanin["cpuif_rd_err"] = "'0"
+            fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_rd_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_rd_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+                fanin["cpuif_rd_data"] = f"{node.inst_name}_fanin_data{array_idx}"
             else:
                 fanin["cpuif_rd_ack"] = self.signal("PREADY", node, "i")
                 fanin["cpuif_rd_err"] = self.signal("PSLVERR", node, "i")
-
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
-
-    def readback(self, node: AddressableNode | None = None) -> str:
-        fanin: dict[str, str] = {}
-        if node is None:
-            fanin["cpuif_rd_data"] = "'0"
-        else:
                 fanin["cpuif_rd_data"] = self.signal("PRDATA", node, "i")
 
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())
+
+    def fanin_intermediate_assignments(
+        self, node: AddressableNode, inst_name: str, array_idx: str, master_prefix: str, indexed_path: str
+    ) -> list[str]:
+        """Generate intermediate signal assignments for APB4 interface arrays."""
+        return [
+            f"assign {inst_name}_fanin_ready{array_idx} = {master_prefix}{indexed_path}.PREADY;",
+            f"assign {inst_name}_fanin_err{array_idx} = {master_prefix}{indexed_path}.PSLVERR;",
+            f"assign {inst_name}_fanin_data{array_idx} = {master_prefix}{indexed_path}.PRDATA;",
+        ]

src/peakrdl_busdecoder/cpuif/apb4/apb4_cpuif_flat.py

@@ -1,50 +1,31 @@
+from collections import deque
+from typing import TYPE_CHECKING
+
 from systemrdl.node import AddressableNode
 
-from ...utils import get_indexed_path
+from ...sv_int import SVInt
+from ...utils import clog2, get_indexed_path
 from ..base_cpuif import BaseCpuif
+from .apb4_interface import APB4FlatInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
 
 
 class APB4CpuifFlat(BaseCpuif):
     template_path = "apb4_tmpl.sv"
-    is_interface = False
 
-    def _port_declaration(self, child: AddressableNode) -> list[str]:
-        return [
-            f"input  logic {self.signal('PCLK', child)}",
-            f"input  logic {self.signal('PRESETn', child)}",
-            f"input  logic {self.signal('PSELx', child)}",
-            f"input  logic {self.signal('PENABLE', child)}",
-            f"input  logic {self.signal('PWRITE', child)}",
-            f"input  logic [{self.addr_width - 1}:0] {self.signal('PADDR', child)}",
-            f"input  logic [2:0] {self.signal('PPROT', child)}",
-            f"input  logic [{self.data_width - 1}:0] {self.signal('PWDATA', child)}",
-            f"input  logic [{self.data_width // 8 - 1}:0] {self.signal('PSTRB', child)}",
-            f"output logic [{self.data_width - 1}:0] {self.signal('PRDATA', child)}",
-            f"output logic {self.signal('PREADY', child)}",
-            f"output logic {self.signal('PSLVERR', child)}",
-        ]
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = APB4FlatInterface(self)
+
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
 
     @property
     def port_declaration(self) -> str:
-        slave_ports: list[str] = [
-            f"input  logic {self.signal('PCLK')}",
-            f"input  logic {self.signal('PRESETn')}",
-            f"input  logic {self.signal('PSELx')}",
-            f"input  logic {self.signal('PENABLE')}",
-            f"input  logic {self.signal('PWRITE')}",
-            f"input  logic [{self.addr_width - 1}:0] {self.signal('PADDR')}",
-            f"input  logic [2:0] {self.signal('PPROT')}",
-            f"input  logic [{self.data_width - 1}:0] {self.signal('PWDATA')}",
-            f"input  logic [{self.data_width // 8 - 1}:0] {self.signal('PSTRB')}",
-            f"output logic [{self.data_width - 1}:0] {self.signal('PRDATA')}",
-            f"output logic {self.signal('PREADY')}",
-            f"output logic {self.signal('PSLVERR')}",
-        ]
-        master_ports: list[str] = []
-        for child in self.addressable_children:
-            master_ports.extend(self._port_declaration(child))
-
-        return ",\n".join(slave_ports + master_ports)
+        return self._interface.get_port_declaration("s_apb_", "m_apb_")
 
     def signal(
         self,
@@ -52,55 +33,53 @@ class APB4CpuifFlat(BaseCpuif):
         node: AddressableNode | None = None,
         idx: str | int | None = None,
     ) -> str:
-        if node is None:
-            # Node is none, so this is a slave signal
-            return f"s_apb_{signal}"
+        return self._interface.signal(signal, node, idx)
 
-        # Master signal
-        base = f"m_apb_{node.inst_name}"
-        if not self.check_is_array(node):
-            # Not an array or an unrolled element
-            if node.current_idx is not None:
-                # This is a specific instance of an unrolled array
-                return f"{base}_{signal}_{'_'.join(map(str, node.current_idx))}"
-            return f"{base}_{signal}"
-        # Is an array
-        if idx is not None:
-            return f"{base}_{signal}[{idx}]"
-        return f"{base}_{signal}[N_{node.inst_name.upper()}S]"
-
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         fanout: dict[str, str] = {}
-        fanout[self.signal("PSELx", node)] = (
-            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'i')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'i')}"
-        )
-        fanout[self.signal("PENABLE", node)] = self.signal("PENABLE")
-        fanout[self.signal("PWRITE", node)] = (
-            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'i')}"
-        )
-        fanout[self.signal("PADDR", node)] = self.signal("PADDR")
-        fanout[self.signal("PPROT", node)] = self.signal("PPROT")
-        fanout[self.signal("PWDATA", node)] = "cpuif_wr_data"
-        fanout[self.signal("PSTRB", node)] = "cpuif_wr_byte_en"
+        addr_comp = [f"{self.signal('PADDR')}"]
+        for i, stride in enumerate(array_stack):
+            addr_comp.append(f"(gi{i}*{SVInt(stride, self.addr_width)})")
 
-        return "\n".join(map(lambda kv: f"assign {kv[0]} = {kv[1]};", fanout.items()))
+        fanout[self.signal("PSEL", node, "gi")] = (
+            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
+        )
+        fanout[self.signal("PENABLE", node, "gi")] = self.signal("PENABLE")
+        fanout[self.signal("PWRITE", node, "gi")] = (
+            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
+        )
+        fanout[self.signal("PADDR", node, "gi")] = f"{{{'-'.join(addr_comp)}}}[{clog2(node.size) - 1}:0]"
+        fanout[self.signal("PPROT", node, "gi")] = self.signal("PPROT")
+        fanout[self.signal("PWDATA", node, "gi")] = "cpuif_wr_data"
+        fanout[self.signal("PSTRB", node, "gi")] = "cpuif_wr_byte_en"
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+        return "\n".join(f"assign {kv[0]} = {kv[1]};" for kv in fanout.items())
+
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_wr_ack"] = "'0"
+            fanin["cpuif_wr_err"] = "'0"
+            if error:
+                fanin["cpuif_wr_ack"] = "'1"
+                fanin["cpuif_wr_err"] = "cpuif_wr_sel.cpuif_err"
+        else:
+            fanin["cpuif_wr_ack"] = self.signal("PREADY", node, "i")
+            fanin["cpuif_wr_err"] = self.signal("PSLVERR", node, "i")
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         fanin: dict[str, str] = {}
         if node is None:
             fanin["cpuif_rd_ack"] = "'0"
             fanin["cpuif_rd_err"] = "'0"
-        else:
-            fanin["cpuif_rd_ack"] = self.signal("PREADY", node)
-            fanin["cpuif_rd_err"] = self.signal("PSLVERR", node)
-
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
-
-    def readback(self, node: AddressableNode | None = None) -> str:
-        fanin: dict[str, str] = {}
-        if node is None:
             fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
         else:
-            fanin["cpuif_rd_data"] = self.signal("PRDATA", node)
+            fanin["cpuif_rd_ack"] = self.signal("PREADY", node, "i")
+            fanin["cpuif_rd_err"] = self.signal("PSLVERR", node, "i")
+            fanin["cpuif_rd_data"] = self.signal("PRDATA", node, "i")
 
-        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
+        return "\n".join(f"{kv[0]} = {kv[1]};" for kv in fanin.items())

src/peakrdl_busdecoder/cpuif/apb4/apb4_interface.py

@@ -0,0 +1,61 @@
+"""APB4-specific interface implementations."""
+
+from systemrdl.node import AddressableNode
+
+from ...utils import clog2
+from ..interface import FlatInterface, SVInterface
+
+
+class APB4SVInterface(SVInterface):
+    """APB4 SystemVerilog interface."""
+
+    def get_interface_type(self) -> str:
+        return "apb4_intf"
+
+    def get_slave_name(self) -> str:
+        return "s_apb"
+
+    def get_master_prefix(self) -> str:
+        return "m_apb_"
+
+
+class APB4FlatInterface(FlatInterface):
+    """APB4 flat signal interface."""
+
+    def get_slave_prefix(self) -> str:
+        return "s_apb_"
+
+    def get_master_prefix(self) -> str:
+        return "m_apb_"
+
+    def _get_slave_port_declarations(self, slave_prefix: str) -> list[str]:
+        return [
+            f"input  logic {slave_prefix}PCLK",
+            f"input  logic {slave_prefix}PRESETn",
+            f"input  logic {slave_prefix}PSEL",
+            f"input  logic {slave_prefix}PENABLE",
+            f"input  logic {slave_prefix}PWRITE",
+            f"input  logic [{self.cpuif.addr_width - 1}:0] {slave_prefix}PADDR",
+            f"input  logic [2:0] {slave_prefix}PPROT",
+            f"input  logic [{self.cpuif.data_width - 1}:0] {slave_prefix}PWDATA",
+            f"input  logic [{self.cpuif.data_width // 8 - 1}:0] {slave_prefix}PSTRB",
+            f"output logic [{self.cpuif.data_width - 1}:0] {slave_prefix}PRDATA",
+            f"output logic {slave_prefix}PREADY",
+            f"output logic {slave_prefix}PSLVERR",
+        ]
+
+    def _get_master_port_declarations(self, child: AddressableNode, master_prefix: str) -> list[str]:
+        return [
+            f"output logic {self.signal('PCLK', child)}",
+            f"output logic {self.signal('PRESETn', child)}",
+            f"output logic {self.signal('PSEL', child)}",
+            f"output logic {self.signal('PENABLE', child)}",
+            f"output logic {self.signal('PWRITE', child)}",
+            f"output logic [{clog2(child.size) - 1}:0] {self.signal('PADDR', child)}",
+            f"output logic [2:0] {self.signal('PPROT', child)}",
+            f"output logic [{self.cpuif.data_width - 1}:0] {self.signal('PWDATA', child)}",
+            f"output logic [{self.cpuif.data_width // 8 - 1}:0] {self.signal('PSTRB', child)}",
+            f"input  logic [{self.cpuif.data_width - 1}:0] {self.signal('PRDATA', child)}",
+            f"input  logic {self.signal('PREADY', child)}",
+            f"input  logic {self.signal('PSLVERR', child)}",
+        ]

src/peakrdl_busdecoder/cpuif/apb4/apb4_tmpl.sv

@@ -6,8 +6,6 @@
         assert_bad_data_width: assert($bits({{cpuif.signal("PWDATA")}}) == {{ds.package_name}}::{{ds.module_name|upper}}_DATA_WIDTH)
             else $error("Interface data width of %0d is incorrect. Shall be %0d bits", $bits({{cpuif.signal("PWDATA")}}), {{ds.package_name}}::{{ds.module_name|upper}}_DATA_WIDTH);
     end
-    assert_wr_sel: assert (@(posedge {{cpuif.signal("PCLK")}}) {{cpuif.signal("PSEL")}} && {{cpuif.signal("PWRITE")}} |-> ##1 ({{cpuif.signal("PREADY")}} || {{cpuif.signal("PSLVERR")}}))
-        else $error("APB4 Slave port SEL implies that cpuif_wr_sel must be one-hot encoded");
 `endif
 {%- endif %}
 
@@ -22,13 +20,20 @@ assign cpuif_wr_data = {{cpuif.signal("PWDATA")}};
 assign cpuif_wr_byte_en = {{cpuif.signal("PSTRB")}};
 
 assign {{cpuif.signal("PRDATA")}} = cpuif_rd_data;
-assign {{cpuif.signal("PREADY")}} = cpuif_rd_ack;
-assign {{cpuif.signal("PSLVERR")}} = cpuif_rd_err | cpuif_rd_sel.cpuif_err | cpuif_wr_sel.cpuif_err;
+assign {{cpuif.signal("PREADY")}} = cpuif_rd_ack | cpuif_wr_ack; 
+assign {{cpuif.signal("PSLVERR")}} = cpuif_rd_err | cpuif_wr_err;
 
 //--------------------------------------------------------------------------
 // Fanout CPU Bus interface signals
 //--------------------------------------------------------------------------
 {{fanout|walk(cpuif=cpuif)}}
+{%- if cpuif.is_interface %}
+
+//--------------------------------------------------------------------------
+// Intermediate signals for interface array fanin
+//--------------------------------------------------------------------------
+{{fanin_intermediate|walk(cpuif=cpuif)}}
+{%- endif %}
 
 //--------------------------------------------------------------------------
 // Fanin CPU Bus interface signals

src/peakrdl_busdecoder/cpuif/axi4lite/axi4_lite_cpuif.py

@@ -1,50 +1,40 @@
-from typing import overload
+from collections import deque
+from typing import TYPE_CHECKING, overload
 
 from systemrdl.node import AddressableNode
 
 from ...utils import get_indexed_path
 from ..base_cpuif import BaseCpuif
+from .axi4_lite_interface import AXI4LiteSVInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
 
 
 class AXI4LiteCpuif(BaseCpuif):
-    template_path = "axi4lite_tmpl.sv"
-    is_interface = True
+    template_path = "axi4_lite_tmpl.sv"
 
-    def _port_declaration(self, child: AddressableNode) -> str:
-        base = f"axi4lite_intf.master m_axil_{child.inst_name}"
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = AXI4LiteSVInterface(self)
 
-        # When unrolled, current_idx is set - append it to the name
-        if child.current_idx is not None:
-            base = f"{base}_{'_'.join(map(str, child.current_idx))}"
-
-        # Only add array dimensions if this should be treated as an array
-        if self.check_is_array(child):
-            assert child.array_dimensions is not None
-            return f"{base} {''.join(f'[{dim}]' for dim in child.array_dimensions)}"
-
-        return base
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
 
     @property
     def port_declaration(self) -> str:
         """Returns the port declaration for the AXI4-Lite interface."""
-        slave_ports: list[str] = ["axi4lite_intf.slave s_axil"]
-        master_ports: list[str] = list(map(self._port_declaration, self.addressable_children))
-
-        return ",\n".join(slave_ports + master_ports)
+        return self._interface.get_port_declaration("s_axil", "m_axil_")
 
     @overload
     def signal(self, signal: str, node: None = None, indexer: None = None) -> str: ...
     @overload
-    def signal(self, signal: str, node: AddressableNode, indexer: str) -> str: ...
+    def signal(self, signal: str, node: AddressableNode, indexer: str | None = None) -> str: ...
     def signal(self, signal: str, node: AddressableNode | None = None, indexer: str | None = None) -> str:
-        if node is None or indexer is None:
-            # Node is none, so this is a slave signal
-            return f"s_axil.{signal}"
+        return self._interface.signal(signal, node, indexer)
 
-        # Master signal
-        return f"m_axil_{get_indexed_path(node.parent, node, indexer, skip_kw_filter=True)}.{signal}"
-
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         fanout: dict[str, str] = {}
 
         wr_sel = f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
@@ -73,23 +63,72 @@ class AXI4LiteCpuif(BaseCpuif):
 
         return "\n".join(f"assign {lhs} = {rhs};" for lhs, rhs in fanout.items())
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_wr_ack"] = "'0"
+            fanin["cpuif_wr_err"] = "'0"
+            if error:
+                fanin["cpuif_wr_ack"] = "'1"
+                fanin["cpuif_wr_err"] = "cpuif_wr_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_wr_ack"] = f"{node.inst_name}_fanin_wr_valid{array_idx}"
+                fanin["cpuif_wr_err"] = f"{node.inst_name}_fanin_wr_err{array_idx}"
+            else:
+                # Read side: ack comes from RVALID; err if RRESP[1] is set (SLVERR/DECERR)
+                fanin["cpuif_wr_ack"] = self.signal("BVALID", node, "i")
+                fanin["cpuif_wr_err"] = f"{self.signal('BRESP', node, 'i')}[1]"
+
+        return "\n".join(f"{lhs} = {rhs};" for lhs, rhs in fanin.items())
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         fanin: dict[str, str] = {}
         if node is None:
             fanin["cpuif_rd_ack"] = "'0"
             fanin["cpuif_rd_err"] = "'0"
+            fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_rd_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_rd_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+                fanin["cpuif_rd_data"] = f"{node.inst_name}_fanin_data{array_idx}"
             else:
-            # Read side: ack comes from RVALID; err if RRESP[1] is set (SLVERR/DECERR)
                 fanin["cpuif_rd_ack"] = self.signal("RVALID", node, "i")
                 fanin["cpuif_rd_err"] = f"{self.signal('RRESP', node, 'i')}[1]"
-
-        return "\n".join(f"{lhs} = {rhs};" for lhs, rhs in fanin.items())
-
-    def readback(self, node: AddressableNode | None = None) -> str:
-        fanin: dict[str, str] = {}
-        if node is None:
-            fanin["cpuif_rd_data"] = "'0"
-        else:
                 fanin["cpuif_rd_data"] = self.signal("RDATA", node, "i")
 
         return "\n".join(f"{lhs} = {rhs};" for lhs, rhs in fanin.items())
+
+    def fanin_intermediate_assignments(
+        self, node: AddressableNode, inst_name: str, array_idx: str, master_prefix: str, indexed_path: str
+    ) -> list[str]:
+        """Generate intermediate signal assignments for AXI4-Lite interface arrays."""
+        return [
+            f"assign {inst_name}_fanin_ready{array_idx} = {master_prefix}{indexed_path}.RVALID;",
+            f"assign {inst_name}_fanin_err{array_idx} = {master_prefix}{indexed_path}.RRESP[1];",
+            f"assign {inst_name}_fanin_data{array_idx} = {master_prefix}{indexed_path}.RDATA;",
+            f"assign {inst_name}_fanin_wr_valid{array_idx} = {master_prefix}{indexed_path}.BVALID;",
+            f"assign {inst_name}_fanin_wr_err{array_idx} = {master_prefix}{indexed_path}.BRESP[1];",
+        ]
+
+    def fanin_intermediate_declarations(self, node: AddressableNode) -> list[str]:
+        if not node.array_dimensions:
+            return []
+
+        array_str = "".join(f"[{dim}]" for dim in node.array_dimensions)
+        return [
+            f"logic {node.inst_name}_fanin_wr_valid{array_str};",
+            f"logic {node.inst_name}_fanin_wr_err{array_str};",
+        ]

src/peakrdl_busdecoder/cpuif/axi4lite/axi4_lite_cpuif_flat.py

@@ -1,58 +1,57 @@
-from typing import overload
+from collections import deque
+from typing import TYPE_CHECKING, overload
 
 from systemrdl.node import AddressableNode
 
-from ...utils import get_indexed_path
+from ...sv_int import SVInt
+from ...utils import clog2, get_indexed_path
 from ..base_cpuif import BaseCpuif
+from .axi4_lite_interface import AXI4LiteFlatInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
 
 
 class AXI4LiteCpuifFlat(BaseCpuif):
-    template_path = "axi4lite_tmpl.sv"
-    is_interface = True
+    """Verilator-friendly variant that flattens the AXI4-Lite interface ports."""
 
-    def _port_declaration(self, child: AddressableNode) -> str:
-        base = f"axi4lite_intf.master m_axil_{child.inst_name}"
+    template_path = "axi4_lite_tmpl.sv"
 
-        # When unrolled, current_idx is set - append it to the name
-        if child.current_idx is not None:
-            base = f"{base}_{'_'.join(map(str, child.current_idx))}"
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = AXI4LiteFlatInterface(self)
 
-        # Only add array dimensions if this should be treated as an array
-        if self.check_is_array(child):
-            assert child.array_dimensions is not None
-            return f"{base} {''.join(f'[{dim}]' for dim in child.array_dimensions)}"
-
-        return base
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
 
     @property
     def port_declaration(self) -> str:
         """Returns the port declaration for the AXI4-Lite interface."""
-        slave_ports: list[str] = ["axi4lite_intf.slave s_axil"]
-        master_ports: list[str] = list(map(self._port_declaration, self.addressable_children))
-
-        return ",\n".join(slave_ports + master_ports)
+        return self._interface.get_port_declaration("s_axil_", "m_axil_")
 
     @overload
     def signal(self, signal: str, node: None = None, indexer: None = None) -> str: ...
     @overload
-    def signal(self, signal: str, node: AddressableNode, indexer: str) -> str: ...
+    def signal(self, signal: str, node: AddressableNode, indexer: str | None = None) -> str: ...
     def signal(self, signal: str, node: AddressableNode | None = None, indexer: str | None = None) -> str:
-        if node is None or indexer is None:
-            # Node is none, so this is a slave signal
-            return f"s_axil.{signal}"
+        return self._interface.signal(signal, node, indexer)
 
-        # Master signal
-        return f"m_axil_{get_indexed_path(node.parent, node, indexer, skip_kw_filter=True)}.{signal}"
-
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         fanout: dict[str, str] = {}
+        waddr_comp = [f"{self.signal('AWADDR')}"]
+        raddr_comp = [f"{self.signal('ARADDR')}"]
+        for i, stride in enumerate(array_stack):
+            offset = f"(gi{i}*{SVInt(stride, self.addr_width)})"
+            waddr_comp.append(offset)
+            raddr_comp.append(offset)
 
         wr_sel = f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
         rd_sel = f"cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
 
         # Write address channel
         fanout[self.signal("AWVALID", node, "gi")] = wr_sel
-        fanout[self.signal("AWADDR", node, "gi")] = self.signal("AWADDR")
+        fanout[self.signal("AWADDR", node, "gi")] = f"{{{'-'.join(waddr_comp)}}}[{clog2(node.size) - 1}:0]"
         fanout[self.signal("AWPROT", node, "gi")] = self.signal("AWPROT")
 
         # Write data channel
@@ -65,7 +64,7 @@ class AXI4LiteCpuifFlat(BaseCpuif):
 
         # Read address channel
         fanout[self.signal("ARVALID", node, "gi")] = rd_sel
-        fanout[self.signal("ARADDR", node, "gi")] = self.signal("ARADDR")
+        fanout[self.signal("ARADDR", node, "gi")] = f"{{{'-'.join(raddr_comp)}}}[{clog2(node.size) - 1}:0]"
         fanout[self.signal("ARPROT", node, "gi")] = self.signal("ARPROT")
 
         # Read data channel (master -> slave)
@@ -73,23 +72,33 @@ class AXI4LiteCpuifFlat(BaseCpuif):
 
         return "\n".join(f"assign {lhs} = {rhs};" for lhs, rhs in fanout.items())
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_wr_ack"] = "'0"
+            fanin["cpuif_wr_err"] = "'0"
+            if error:
+                fanin["cpuif_wr_ack"] = "'1"
+                fanin["cpuif_wr_err"] = "cpuif_wr_sel.cpuif_err"
+        else:
+            # Read side: ack comes from RVALID; err if RRESP[1] is set (SLVERR/DECERR)
+            fanin["cpuif_wr_ack"] = self.signal("BVALID", node, "i")
+            fanin["cpuif_wr_err"] = f"{self.signal('BRESP', node, 'i')}[1]"
+
+        return "\n".join(f"{lhs} = {rhs};" for lhs, rhs in fanin.items())
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         fanin: dict[str, str] = {}
         if node is None:
             fanin["cpuif_rd_ack"] = "'0"
             fanin["cpuif_rd_err"] = "'0"
+            fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
         else:
-            # Read side: ack comes from RVALID; err if RRESP[1] is set (SLVERR/DECERR)
             fanin["cpuif_rd_ack"] = self.signal("RVALID", node, "i")
             fanin["cpuif_rd_err"] = f"{self.signal('RRESP', node, 'i')}[1]"
-
-        return "\n".join(f"{lhs} = {rhs};" for lhs, rhs in fanin.items())
-
-    def readback(self, node: AddressableNode | None = None) -> str:
-        fanin: dict[str, str] = {}
-        if node is None:
-            fanin["cpuif_rd_data"] = "'0"
-        else:
             fanin["cpuif_rd_data"] = self.signal("RDATA", node, "i")
 
         return "\n".join(f"{lhs} = {rhs};" for lhs, rhs in fanin.items())

src/peakrdl_busdecoder/cpuif/axi4lite/axi4_lite_interface.py

@@ -0,0 +1,85 @@
+"""AXI4-Lite-specific interface implementations."""
+
+from systemrdl.node import AddressableNode
+
+from ...utils import clog2
+from ..interface import FlatInterface, SVInterface
+
+
+class AXI4LiteSVInterface(SVInterface):
+    """AXI4-Lite SystemVerilog interface."""
+
+    def get_interface_type(self) -> str:
+        return "axi4lite_intf"
+
+    def get_slave_name(self) -> str:
+        return "s_axil"
+
+    def get_master_prefix(self) -> str:
+        return "m_axil_"
+
+
+class AXI4LiteFlatInterface(FlatInterface):
+    """AXI4-Lite flat signal interface."""
+
+    def get_slave_prefix(self) -> str:
+        return "s_axil_"
+
+    def get_master_prefix(self) -> str:
+        return "m_axil_"
+
+    def _get_slave_port_declarations(self, slave_prefix: str) -> list[str]:
+        return [
+            # Write address channel
+            f"input  logic {slave_prefix}AWVALID",
+            f"output logic {slave_prefix}AWREADY",
+            f"input  logic [{self.cpuif.addr_width - 1}:0] {slave_prefix}AWADDR",
+            f"input  logic [2:0] {slave_prefix}AWPROT",
+            # Write data channel
+            f"input  logic {slave_prefix}WVALID",
+            f"output logic {slave_prefix}WREADY",
+            f"input  logic [{self.cpuif.data_width - 1}:0] {slave_prefix}WDATA",
+            f"input  logic [{self.cpuif.data_width // 8 - 1}:0] {slave_prefix}WSTRB",
+            # Write response channel
+            f"output logic {slave_prefix}BVALID",
+            f"input  logic {slave_prefix}BREADY",
+            f"output logic [1:0] {slave_prefix}BRESP",
+            # Read address channel
+            f"input  logic {slave_prefix}ARVALID",
+            f"output logic {slave_prefix}ARREADY",
+            f"input  logic [{self.cpuif.addr_width - 1}:0] {slave_prefix}ARADDR",
+            f"input  logic [2:0] {slave_prefix}ARPROT",
+            # Read data channel
+            f"output logic {slave_prefix}RVALID",
+            f"input  logic {slave_prefix}RREADY",
+            f"output logic [{self.cpuif.data_width - 1}:0] {slave_prefix}RDATA",
+            f"output logic [1:0] {slave_prefix}RRESP",
+        ]
+
+    def _get_master_port_declarations(self, child: AddressableNode, master_prefix: str) -> list[str]:
+        return [
+            # Write address channel
+            f"output logic {self.signal('AWVALID', child)}",
+            f"input  logic {self.signal('AWREADY', child)}",
+            f"output logic [{clog2(child.size) - 1}:0] {self.signal('AWADDR', child)}",
+            f"output logic [2:0] {self.signal('AWPROT', child)}",
+            # Write data channel
+            f"output logic {self.signal('WVALID', child)}",
+            f"input  logic {self.signal('WREADY', child)}",
+            f"output logic [{self.cpuif.data_width - 1}:0] {self.signal('WDATA', child)}",
+            f"output logic [{self.cpuif.data_width // 8 - 1}:0] {self.signal('WSTRB', child)}",
+            # Write response channel
+            f"input  logic {self.signal('BVALID', child)}",
+            f"output logic {self.signal('BREADY', child)}",
+            f"input  logic [1:0] {self.signal('BRESP', child)}",
+            # Read address channel
+            f"output logic {self.signal('ARVALID', child)}",
+            f"input  logic {self.signal('ARREADY', child)}",
+            f"output logic [{clog2(child.size) - 1}:0] {self.signal('ARADDR', child)}",
+            f"output logic [2:0] {self.signal('ARPROT', child)}",
+            # Read data channel
+            f"input  logic {self.signal('RVALID', child)}",
+            f"output logic {self.signal('RREADY', child)}",
+            f"input  logic [{self.cpuif.data_width - 1}:0] {self.signal('RDATA', child)}",
+            f"input  logic [1:0] {self.signal('RRESP', child)}",
+        ]

src/peakrdl_busdecoder/cpuif/axi4lite/axi4_lite_tmpl.sv

@@ -15,6 +15,7 @@
                         $bits({{cpuif.signal("WDATA")}}), {{ds.package_name}}::{{ds.module_name|upper}}_DATA_WIDTH);
     end
 
+    `ifdef PEAKRDL_ASSERTIONS
     // Simple handshake sanity (one-cycle implication; relax/adjust as needed)
     assert_rd_resp_enc: assert property (@(posedge {{cpuif.signal("ACLK")}})
         {{cpuif.signal("RVALID")}} |-> (^{{cpuif.signal("RRESP")}} !== 1'bx))
@@ -24,11 +25,24 @@
         {{cpuif.signal("BVALID")}} |-> (^{{cpuif.signal("BRESP")}} !== 1'bx))
             else $error("BRESP must be a legal AXI response when BVALID is high");
     `endif
+`endif
 {% endif -%}
 
+logic axi_wr_valid;
+logic axi_wr_invalid;
+logic cpuif_wr_ack_int;
+logic cpuif_rd_ack_int;
+
+assign axi_wr_valid = {{cpuif.signal("AWVALID")}} & {{cpuif.signal("WVALID")}};
+assign axi_wr_invalid = {{cpuif.signal("AWVALID")}} ^ {{cpuif.signal("WVALID")}};
+
+// Ready/acceptance follows the simplified single-beat requirement
+assign {{cpuif.signal("AWREADY")}} = axi_wr_valid;
+assign {{cpuif.signal("WREADY")}}  = axi_wr_valid;
+assign {{cpuif.signal("ARREADY")}} = {{cpuif.signal("ARVALID")}};
 
 assign cpuif_req     = {{cpuif.signal("AWVALID")}} | {{cpuif.signal("ARVALID")}};
-assign cpuif_wr_en   = {{cpuif.signal("AWVALID")}} & {{cpuif.signal("WVALID")}};
+assign cpuif_wr_en   = axi_wr_valid;
 assign cpuif_rd_en   = {{cpuif.signal("ARVALID")}};
 
 assign cpuif_wr_addr = {{cpuif.signal("AWADDR")}};
@@ -42,17 +56,26 @@ assign cpuif_wr_byte_en = {{cpuif.signal("WSTRB")}};
 // Read: ack=RVALID, err=RRESP[1] (SLVERR/DECERR), data=RDATA
 //
 assign {{cpuif.signal("RDATA")}}  = cpuif_rd_data;
-assign {{cpuif.signal("RVALID")}} = cpuif_rd_ack;
+assign cpuif_rd_ack_int = cpuif_rd_ack | cpuif_rd_sel.cpuif_err;
+assign {{cpuif.signal("RVALID")}} = cpuif_rd_ack_int;
 assign {{cpuif.signal("RRESP")}}  = (cpuif_rd_err | cpuif_rd_sel.cpuif_err | cpuif_wr_sel.cpuif_err) ? 2'b10 : 2'b00;
 
 // Write: ack=BVALID, err=BRESP[1]
-assign {{cpuif.signal("BVALID")}} = cpuif_wr_ack;
-assign {{cpuif.signal("BRESP")}}  = (cpuif_wr_err | cpuif_wr_sel.cpuif_err | cpuif_rd_sel.cpuif_err) ? 2'b10 : 2'b00;
+assign cpuif_wr_ack_int = cpuif_wr_ack | cpuif_wr_sel.cpuif_err | axi_wr_invalid;
+assign {{cpuif.signal("BVALID")}} = cpuif_wr_ack_int;
+assign {{cpuif.signal("BRESP")}}  = (cpuif_wr_err | cpuif_wr_sel.cpuif_err | cpuif_rd_sel.cpuif_err | axi_wr_invalid) ? 2'b10 : 2'b00;
 
 //--------------------------------------------------------------------------
 // Fanout CPU Bus interface signals
 //--------------------------------------------------------------------------
 {{fanout|walk(cpuif=cpuif)}}
+{%- if cpuif.is_interface %}
+
+//--------------------------------------------------------------------------
+// Intermediate signals for interface array fanin
+//--------------------------------------------------------------------------
+{{fanin_intermediate|walk(cpuif=cpuif)}}
+{%- endif %}
 
 //--------------------------------------------------------------------------
 // Fanin CPU Bus interface signals

src/peakrdl_busdecoder/cpuif/base_cpuif.py

@@ -1,5 +1,6 @@
 import inspect
 import os
+from collections import deque
 from typing import TYPE_CHECKING
 
 import jinja2 as jj
@@ -7,6 +8,7 @@ from systemrdl.node import AddressableNode
 
 from ..utils import clog2, get_indexed_path, is_pow2, roundup_pow2
 from .fanin_gen import FaninGenerator
+from .fanin_intermediate_gen import FaninIntermediateGenerator
 from .fanout_gen import FanoutGenerator
 
 if TYPE_CHECKING:
@@ -24,11 +26,7 @@ class BaseCpuif:
 
     @property
     def addressable_children(self) -> list[AddressableNode]:
-        return [
-            child
-            for child in self.exp.ds.top_node.children(unroll=self.unroll)
-            if isinstance(child, AddressableNode)
-        ]
+        return self.exp.ds.get_addressable_children_at_depth(unroll=self.unroll)
 
     @property
     def addr_width(self) -> int:
@@ -84,19 +82,20 @@ class BaseCpuif:
             loader=loader,
             undefined=jj.StrictUndefined,
         )
-        jj_env.tests["array"] = self.check_is_array  # type: ignore
-        jj_env.filters["clog2"] = clog2  # type: ignore
-        jj_env.filters["is_pow2"] = is_pow2  # type: ignore
-        jj_env.filters["roundup_pow2"] = roundup_pow2  # type: ignore
-        jj_env.filters["address_slice"] = self.get_address_slice  # type: ignore
-        jj_env.filters["get_path"] = lambda x: get_indexed_path(self.exp.ds.top_node, x, "i")  # type: ignore
-        jj_env.filters["walk"] = self.exp.walk  # type: ignore
+        jj_env.tests["array"] = self.check_is_array
+        jj_env.filters["clog2"] = clog2
+        jj_env.filters["is_pow2"] = is_pow2
+        jj_env.filters["roundup_pow2"] = roundup_pow2
+        jj_env.filters["address_slice"] = self.get_address_slice
+        jj_env.filters["get_path"] = lambda x: get_indexed_path(self.exp.ds.top_node, x, "i")
+        jj_env.filters["walk"] = self.exp.walk
 
-        context = {  # type: ignore
+        context = {
             "cpuif": self,
             "ds": self.exp.ds,
             "fanout": FanoutGenerator,
             "fanin": FaninGenerator,
+            "fanin_intermediate": FaninIntermediateGenerator,
         }
 
         template = jj_env.get_template(self.template_path)
@@ -108,11 +107,36 @@ class BaseCpuif:
 
         return f"({cpuif_addr} - 'h{addr:x})[{clog2(size) - 1}:0]"
 
-    def fanout(self, node: AddressableNode) -> str:
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
         raise NotImplementedError
 
-    def fanin(self, node: AddressableNode | None = None) -> str:
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         raise NotImplementedError
 
-    def readback(self, node: AddressableNode | None = None) -> str:
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
         raise NotImplementedError
+
+    def fanin_intermediate_assignments(
+        self, node: AddressableNode, inst_name: str, array_idx: str, master_prefix: str, indexed_path: str
+    ) -> list[str]:
+        """Generate intermediate signal assignments for interface array fanin.
+
+        This method should be implemented by cpuif classes that use interfaces.
+        It returns a list of assignment strings that copy signals from interface
+        arrays to intermediate unpacked arrays using constant (genvar) indexing.
+
+        Args:
+            node: The addressable node
+            inst_name: Instance name for the intermediate signals
+            array_idx: Array index string (e.g., "[gi0][gi1]")
+            master_prefix: Master interface prefix
+            indexed_path: Indexed path to the interface element
+
+        Returns:
+            List of assignment strings
+        """
+        return []  # Default: no intermediate assignments needed
+
+    def fanin_intermediate_declarations(self, node: AddressableNode) -> list[str]:
+        """Optional extra intermediate signal declarations for interface arrays."""
+        return []

src/peakrdl_busdecoder/cpuif/fanin_gen.py

@@ -20,13 +20,24 @@ class FaninGenerator(BusDecoderListener):
 
         self._stack: deque[Body] = deque()
         cb = CombinationalBody()
-        cb += cpuif.fanin()
-        cb += cpuif.readback()
+        cb += cpuif.fanin_wr()
+        cb += cpuif.fanin_rd()
         self._stack.append(cb)
 
     def enter_AddressableComponent(self, node: AddressableNode) -> WalkerAction | None:
         action = super().enter_AddressableComponent(node)
 
+        should_generate = action == WalkerAction.SkipDescendants
+        if not should_generate and self._ds.max_decode_depth == 0:
+            for child in node.children():
+                if isinstance(child, AddressableNode):
+                    break
+            else:
+                should_generate = True
+
+        if not should_generate:
+            return action
+
         if node.array_dimensions:
             for i, dim in enumerate(node.array_dimensions):
                 fb = ForLoopBody(
@@ -36,17 +47,14 @@ class FaninGenerator(BusDecoderListener):
                 )
                 self._stack.append(fb)
 
-        if action == WalkerAction.Continue:
         ifb = IfBody()
-            with ifb.cm(
-                f"cpuif_rd_sel.{get_indexed_path(self._cpuif.exp.ds.top_node, node)} || cpuif_wr_sel.{get_indexed_path(self._cpuif.exp.ds.top_node, node)}"
-            ) as b:
-                b += self._cpuif.fanin(node)
+        with ifb.cm(f"cpuif_wr_sel.{get_indexed_path(self._cpuif.exp.ds.top_node, node)}") as b:
+            b += self._cpuif.fanin_wr(node)
         self._stack[-1] += ifb
 
         ifb = IfBody()
         with ifb.cm(f"cpuif_rd_sel.{get_indexed_path(self._cpuif.exp.ds.top_node, node)}") as b:
-                b += self._cpuif.readback(node)
+            b += self._cpuif.fanin_rd(node)
         self._stack[-1] += ifb
 
         return action
@@ -62,4 +70,14 @@ class FaninGenerator(BusDecoderListener):
         super().exit_AddressableComponent(node)
 
     def __str__(self) -> str:
+        wr_ifb = IfBody()
+        with wr_ifb.cm("cpuif_wr_sel.cpuif_err") as b:
+            b += self._cpuif.fanin_wr(error=True)
+        self._stack[-1] += wr_ifb
+
+        rd_ifb = IfBody()
+        with rd_ifb.cm("cpuif_rd_sel.cpuif_err") as b:
+            b += self._cpuif.fanin_rd(error=True)
+        self._stack[-1] += rd_ifb
+
         return "\n".join(map(str, self._stack))

src/peakrdl_busdecoder/cpuif/fanin_intermediate_gen.py

@@ -0,0 +1,145 @@
+"""Generator for intermediate signals needed for interface array fanin.
+
+When using SystemVerilog interface arrays, we cannot use variable indices
+in procedural blocks (like always_comb). This generator creates intermediate
+signals that copy from interface arrays using generate loops, which can then
+be safely accessed with variable indices in the fanin logic.
+"""
+
+from collections import deque
+from typing import TYPE_CHECKING
+
+from systemrdl.node import AddressableNode
+from systemrdl.walker import WalkerAction
+
+from ..body import Body, ForLoopBody
+from ..design_state import DesignState
+from ..listener import BusDecoderListener
+from ..utils import get_indexed_path
+
+if TYPE_CHECKING:
+    from .base_cpuif import BaseCpuif
+
+
+class FaninIntermediateGenerator(BusDecoderListener):
+    """Generates intermediate signals for interface array fanin."""
+
+    def __init__(self, ds: DesignState, cpuif: "BaseCpuif") -> None:
+        super().__init__(ds)
+        self._cpuif = cpuif
+        self._declarations: list[str] = []
+        self._stack: deque[Body] = deque()
+        self._stack.append(Body())
+
+    def enter_AddressableComponent(self, node: AddressableNode) -> WalkerAction | None:
+        action = super().enter_AddressableComponent(node)
+
+        # Only generate intermediates for interface arrays
+        # Check if cpuif has is_interface attribute (some implementations don't)
+        is_interface = getattr(self._cpuif, "is_interface", False)
+        if not is_interface or not node.array_dimensions:
+            return action
+
+        # Generate intermediate signal declarations
+        self._generate_intermediate_declarations(node)
+
+        # Generate assignment logic using generate loops
+        if node.array_dimensions:
+            for i, dim in enumerate(node.array_dimensions):
+                fb = ForLoopBody(
+                    "genvar",
+                    f"gi{i}",
+                    dim,
+                )
+                self._stack.append(fb)
+
+        # Generate assignments from interface array to intermediates
+        self._stack[-1] += self._generate_intermediate_assignments(node)
+
+        return action
+
+    def exit_AddressableComponent(self, node: AddressableNode) -> None:
+        is_interface = getattr(self._cpuif, "is_interface", False)
+        if is_interface and node.array_dimensions:
+            for _ in node.array_dimensions:
+                b = self._stack.pop()
+                if not b:
+                    continue
+                self._stack[-1] += b
+
+        super().exit_AddressableComponent(node)
+
+    def _generate_intermediate_declarations(self, node: AddressableNode) -> None:
+        """Generate intermediate signal declarations for a node."""
+        inst_name = node.inst_name
+
+        # Array dimensions should be checked before calling this function
+        if not node.array_dimensions:
+            return
+
+        # Calculate total array size
+        array_size = 1
+        for dim in node.array_dimensions:
+            array_size *= dim
+
+        # Create array dimension string
+        array_str = "".join(f"[{dim}]" for dim in node.array_dimensions)
+
+        # Generate declarations for each fanin signal
+        # For APB3/4: PREADY, PSLVERR, PRDATA
+        # These are the signals read in fanin
+        self._declarations.append(f"logic {inst_name}_fanin_ready{array_str};")
+        self._declarations.append(f"logic {inst_name}_fanin_err{array_str};")
+        self._declarations.append(
+            f"logic [{self._cpuif.data_width - 1}:0] {inst_name}_fanin_data{array_str};"
+        )
+
+        # Allow CPU interface to add extra intermediate declarations (e.g., write responses)
+        self._declarations.extend(self._cpuif.fanin_intermediate_declarations(node))
+
+    def _generate_intermediate_assignments(self, node: AddressableNode) -> str:
+        """Generate assignments from interface array to intermediate signals."""
+        inst_name = node.inst_name
+        indexed_path = get_indexed_path(node.parent, node, "gi", skip_kw_filter=True)
+
+        # Get master prefix - use getattr to avoid type errors
+        interface = getattr(self._cpuif, "_interface", None)
+        if interface is None:
+            return ""
+        master_prefix = interface.get_master_prefix()
+
+        # Array dimensions should be checked before calling this function
+        if not node.array_dimensions:
+            return ""
+
+        # Create indexed signal names for left-hand side
+        array_idx = "".join(f"[gi{i}]" for i in range(len(node.array_dimensions)))
+
+        # Delegate to cpuif to get the appropriate assignments for this interface type
+        assignments = self._cpuif.fanin_intermediate_assignments(
+            node, inst_name, array_idx, master_prefix, indexed_path
+        )
+
+        return "\n".join(assignments)
+
+    def get_declarations(self) -> str:
+        """Get all intermediate signal declarations."""
+        if not self._declarations:
+            return ""
+        return "\n".join(self._declarations)
+
+    def __str__(self) -> str:
+        """Get all intermediate signal declarations and assignments."""
+        if not self._declarations:
+            return ""
+
+        # Output declarations first
+        output = "\n".join(self._declarations)
+        output += "\n\n"
+
+        # Then output assignments
+        body_str = "\n".join(map(str, self._stack))
+        if body_str and body_str.strip():
+            output += body_str
+
+        return output

src/peakrdl_busdecoder/cpuif/fanout_gen.py

@@ -23,6 +23,17 @@ class FanoutGenerator(BusDecoderListener):
     def enter_AddressableComponent(self, node: AddressableNode) -> WalkerAction | None:
         action = super().enter_AddressableComponent(node)
 
+        should_generate = action == WalkerAction.SkipDescendants
+        if not should_generate and self._ds.max_decode_depth == 0:
+            for child in node.children():
+                if isinstance(child, AddressableNode):
+                    break
+            else:
+                should_generate = True
+
+        if not should_generate:
+            return action
+
         if node.array_dimensions:
             for i, dim in enumerate(node.array_dimensions):
                 fb = ForLoopBody(
@@ -32,8 +43,7 @@ class FanoutGenerator(BusDecoderListener):
                 )
                 self._stack.append(fb)
 
-        if action == WalkerAction.Continue:
-            self._stack[-1] += self._cpuif.fanout(node)
+        self._stack[-1] += self._cpuif.fanout(node, self._array_stride_stack)
 
         return action
 

src/peakrdl_busdecoder/cpuif/interface.py

@@ -0,0 +1,202 @@
+"""Interface abstraction for handling flat and non-flat signal declarations."""
+
+import re
+from abc import ABC, abstractmethod
+from typing import TYPE_CHECKING
+
+from systemrdl.node import AddressableNode
+
+from ..utils import get_indexed_path
+
+if TYPE_CHECKING:
+    from .base_cpuif import BaseCpuif
+
+
+class Interface(ABC):
+    """Abstract base class for interface signal handling."""
+
+    def __init__(self, cpuif: "BaseCpuif") -> None:
+        self.cpuif = cpuif
+
+    @property
+    @abstractmethod
+    def is_interface(self) -> bool:
+        """Whether this uses SystemVerilog interfaces."""
+        ...
+
+    @abstractmethod
+    def get_port_declaration(self, slave_name: str, master_prefix: str) -> str:
+        """
+        Generate port declarations for the interface.
+
+        Args:
+            slave_name: Name of the slave interface/signal prefix
+            master_prefix: Prefix for master interfaces/signals
+
+        Returns:
+            Port declarations as a string
+        """
+        ...
+
+    @abstractmethod
+    def signal(
+        self,
+        signal: str,
+        node: AddressableNode | None = None,
+        indexer: str | int | None = None,
+    ) -> str:
+        """
+        Generate signal reference.
+
+        Args:
+            signal: Signal name
+            node: Optional addressable node for master signals
+            indexer: Optional indexer for arrays.
+                     For SVInterface: str like "i" or "gi" for loop indices
+                     For FlatInterface: str or int for array subscript
+
+        Returns:
+            Signal reference as a string
+        """
+        ...
+
+
+class SVInterface(Interface):
+    """SystemVerilog interface-based signal handling."""
+
+    slave_modport_name = "slave"
+    master_modport_name = "master"
+
+    @property
+    def is_interface(self) -> bool:
+        return True
+
+    def get_port_declaration(self, slave_name: str, master_prefix: str) -> str:
+        """Generate SystemVerilog interface port declarations."""
+        slave_ports: list[str] = [f"{self.get_interface_type()}.{self.slave_modport_name} {slave_name}"]
+        master_ports: list[str] = []
+
+        for child in self.cpuif.addressable_children:
+            base = f"{self.get_interface_type()}.{self.master_modport_name} {master_prefix}{child.inst_name}"
+
+            # When unrolled, current_idx is set - append it to the name
+            if child.current_idx is not None:
+                base = f"{base}_{'_'.join(map(str, child.current_idx))}"  # ty: ignore
+
+            # Only add array dimensions if this should be treated as an array
+            if self.cpuif.check_is_array(child):
+                assert child.array_dimensions is not None
+                base = f"{base} {''.join(f'[{dim}]' for dim in child.array_dimensions)}"
+
+            master_ports.append(base)
+
+        return ",\n".join(slave_ports + master_ports)
+
+    def signal(
+        self,
+        signal: str,
+        node: AddressableNode | None = None,
+        indexer: str | int | None = None,
+    ) -> str:
+        """Generate SystemVerilog interface signal reference."""
+
+        # SVInterface only supports string indexers (loop variable names like "i", "gi")
+        if indexer is not None and not isinstance(indexer, str):
+            raise TypeError(f"SVInterface.signal() requires string indexer, got {type(indexer).__name__}")
+
+        if node is None or indexer is None:
+            # Node is none, so this is a slave signal
+            slave_name = self.get_slave_name()
+            return f"{slave_name}.{signal}"
+
+        # Master signal
+        master_prefix = self.get_master_prefix()
+        return f"{master_prefix}{get_indexed_path(node.parent, node, indexer, skip_kw_filter=True)}.{signal}"
+
+    @abstractmethod
+    def get_interface_type(self) -> str:
+        """Get the SystemVerilog interface type name."""
+        ...
+
+    @abstractmethod
+    def get_slave_name(self) -> str:
+        """Get the slave interface instance name."""
+        ...
+
+    @abstractmethod
+    def get_master_prefix(self) -> str:
+        """Get the master interface name prefix."""
+        ...
+
+
+class FlatInterface(Interface):
+    """Flat signal-based interface handling."""
+
+    @property
+    def is_interface(self) -> bool:
+        return False
+
+    def get_port_declaration(self, slave_name: str, master_prefix: str) -> str:
+        """Generate flat port declarations."""
+        slave_ports = self._get_slave_port_declarations(slave_name)
+        master_ports: list[str] = []
+
+        for child in self.cpuif.addressable_children:
+            master_ports.extend(self._get_master_port_declarations(child, master_prefix))
+
+        return ",\n".join(slave_ports + master_ports)
+
+    def signal(
+        self,
+        signal: str,
+        node: AddressableNode | None = None,
+        indexer: str | int | None = None,
+    ) -> str:
+        """Generate flat signal reference."""
+        if node is None:
+            # Node is none, so this is a slave signal
+            slave_prefix = self.get_slave_prefix()
+            return f"{slave_prefix}{signal}"
+
+        # Master signal
+        master_prefix = self.get_master_prefix()
+        base = f"{master_prefix}{node.inst_name}"
+
+        if not self.cpuif.check_is_array(node):
+            # Not an array or an unrolled element
+            if node.current_idx is not None:
+                # This is a specific instance of an unrolled array
+                return f"{base}_{signal}_{'_'.join(map(str, node.current_idx))}"
+            return f"{base}_{signal}"
+
+        # Is an array
+        if indexer is not None:
+            if isinstance(indexer, str):
+                indexed_path = get_indexed_path(node.parent, node, indexer, skip_kw_filter=True)
+                pattern = r"\[.*?\]"
+                indexes = re.findall(pattern, indexed_path)
+
+                return f"{base}_{signal}{''.join(indexes)}"
+
+            return f"{base}_{signal}[{indexer}]"
+        return f"{base}_{signal}[N_{node.inst_name.upper()}S]"
+
+    @abstractmethod
+    def _get_slave_port_declarations(self, slave_prefix: str) -> list[str]:
+        """Get slave port declarations."""
+        ...
+
+    @abstractmethod
+    def _get_master_port_declarations(self, child: AddressableNode, master_prefix: str) -> list[str]:
+        """Get master port declarations for a child node."""
+        ...
+
+    @abstractmethod
+    def get_slave_prefix(self) -> str:
+        """Get the slave signal name prefix."""
+        ...
+
+    @abstractmethod
+    def get_master_prefix(self) -> str:
+        """Get the master signal name prefix."""
+        ...

src/peakrdl_busdecoder/cpuif/taxi_apb/__init__.py

@@ -0,0 +1,3 @@
+from .taxi_apb_cpuif import TaxiAPBCpuif
+
+__all__ = ["TaxiAPBCpuif"]

src/peakrdl_busdecoder/cpuif/taxi_apb/taxi_apb_cpuif.py

@@ -0,0 +1,109 @@
+from collections import deque
+from typing import TYPE_CHECKING, overload
+
+from systemrdl.node import AddressableNode
+
+from ...utils import get_indexed_path
+from ..base_cpuif import BaseCpuif
+from .taxi_apb_interface import TaxiAPBSVInterface
+
+if TYPE_CHECKING:
+    from ...exporter import BusDecoderExporter
+
+
+class TaxiAPBCpuif(BaseCpuif):
+    template_path = "taxi_apb_tmpl.sv"
+
+    def __init__(self, exp: "BusDecoderExporter") -> None:
+        super().__init__(exp)
+        self._interface = TaxiAPBSVInterface(self)
+        self._interface.master_modport_name = "mst"
+        self._interface.slave_modport_name = "slv"
+
+    @property
+    def is_interface(self) -> bool:
+        return self._interface.is_interface
+
+    @property
+    def port_declaration(self) -> str:
+        """Returns the port declaration for the APB4 interface."""
+        return self._interface.get_port_declaration("s_apb", "m_apb_")
+
+    @overload
+    def signal(self, signal: str, node: None = None, indexer: None = None) -> str: ...
+    @overload
+    def signal(self, signal: str, node: AddressableNode, indexer: str) -> str: ...
+    def signal(self, signal: str, node: AddressableNode | None = None, indexer: str | None = None) -> str:
+        return self._interface.signal(signal, node, indexer)
+
+    def fanout(self, node: AddressableNode, array_stack: deque[int]) -> str:
+        fanout: dict[str, str] = {}
+        fanout[self.signal("psel", node, "gi")] = (
+            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}|cpuif_rd_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
+        )
+        fanout[self.signal("penable", node, "gi")] = self.signal("penable")
+        fanout[self.signal("pwrite", node, "gi")] = (
+            f"cpuif_wr_sel.{get_indexed_path(self.exp.ds.top_node, node, 'gi')}"
+        )
+        fanout[self.signal("paddr", node, "gi")] = self.signal("paddr")
+        fanout[self.signal("pprot", node, "gi")] = self.signal("pprot")
+        fanout[self.signal("pwdata", node, "gi")] = "cpuif_wr_data"
+        fanout[self.signal("pstrb", node, "gi")] = "cpuif_wr_byte_en"
+        # no user?
+
+        return "\n".join(map(lambda kv: f"assign {kv[0]} = {kv[1]};", fanout.items()))
+
+    def fanin_wr(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_rd_ack"] = "'0"
+            fanin["cpuif_rd_err"] = "'0"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_rd_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_rd_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+            else:
+                fanin["cpuif_rd_ack"] = self.signal("pready", node, "i")
+                fanin["cpuif_rd_err"] = self.signal("pslverr", node, "i")
+
+        # no user?
+        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
+
+    def fanin_rd(self, node: AddressableNode | None = None, *, error: bool = False) -> str:
+        fanin: dict[str, str] = {}
+        if node is None:
+            fanin["cpuif_rd_ack"] = "'0"
+            fanin["cpuif_rd_err"] = "'0"
+            fanin["cpuif_rd_data"] = "'0"
+            if error:
+                fanin["cpuif_rd_ack"] = "'1"
+                fanin["cpuif_rd_err"] = "cpuif_rd_sel.cpuif_err"
+        else:
+            # Use intermediate signals for interface arrays to avoid
+            # non-constant indexing of interface arrays in procedural blocks
+            if self.is_interface and node.is_array and node.array_dimensions:
+                # Generate array index string [i0][i1]... for the intermediate signal
+                array_idx = "".join(f"[i{i}]" for i in range(len(node.array_dimensions)))
+                fanin["cpuif_rd_ack"] = f"{node.inst_name}_fanin_ready{array_idx}"
+                fanin["cpuif_rd_err"] = f"{node.inst_name}_fanin_err{array_idx}"
+                fanin["cpuif_rd_data"] = f"{node.inst_name}_fanin_data{array_idx}"
+            else:
+                fanin["cpuif_rd_ack"] = self.signal("prdata", node, "i")
+                fanin["cpuif_rd_err"] = self.signal("pslverr", node, "i")
+                fanin["cpuif_rd_data"] = self.signal("prdata", node, "i")
+
+        return "\n".join(map(lambda kv: f"{kv[0]} = {kv[1]};", fanin.items()))
+
+    def fanin_intermediate_assignments(
+        self, node: AddressableNode, inst_name: str, array_idx: str, master_prefix: str, indexed_path: str
+    ) -> list[str]:
+        """Generate intermediate signal assignments for APB4 interface arrays."""
+        return [
+            f"assign {inst_name}_fanin_ready{array_idx} = {master_prefix}{indexed_path}.pready;",
+            f"assign {inst_name}_fanin_err{array_idx} = {master_prefix}{indexed_path}.pslverr;",
+            f"assign {inst_name}_fanin_data{array_idx} = {master_prefix}{indexed_path}.prdata;",
+        ]

src/peakrdl_busdecoder/cpuif/taxi_apb/taxi_apb_interface.py

@@ -0,0 +1,16 @@
+"""Taxi APB-specific interface implementations."""
+
+from ..interface import SVInterface
+
+
+class TaxiAPBSVInterface(SVInterface):
+    """Taxi APB SystemVerilog interface."""
+
+    def get_interface_type(self) -> str:
+        return "taxi_apb_if"
+
+    def get_slave_name(self) -> str:
+        return "s_apb"
+
+    def get_master_prefix(self) -> str:
+        return "m_apb_"

src/peakrdl_busdecoder/cpuif/taxi_apb/taxi_apb_tmpl.sv

@@ -0,0 +1,44 @@
+{%- if cpuif.is_interface %}
+`ifndef SYNTHESIS
+    initial begin
+        assert_bad_addr_width: assert($bits({{cpuif.signal("paddr")}}) >= {{ds.package_name}}::{{ds.module_name|upper}}_MIN_ADDR_WIDTH)
+            else $error("Interface address width of %0d is too small. Shall be at least %0d bits", $bits({{cpuif.signal("paddr")}}), {{ds.package_name}}::{{ds.module_name|upper}}_MIN_ADDR_WIDTH);
+        assert_bad_data_width: assert($bits({{cpuif.signal("pwdata")}}) == {{ds.package_name}}::{{ds.module_name|upper}}_DATA_WIDTH)
+            else $error("Interface data width of %0d is incorrect. Shall be %0d bits", $bits({{cpuif.signal("pwdata")}}), {{ds.package_name}}::{{ds.module_name|upper}}_DATA_WIDTH);
+    end
+    `ifdef PEAKRDL_ASSERTIONS
+    assert_wr_sel: assert property (@(posedge {{cpuif.signal("PCLK")}}) {{cpuif.signal("psel")}} && {{cpuif.signal("pwrite")}} |-> ##1 ({{cpuif.signal("pready")}} || {{cpuif.signal("pslverr")}}))
+        else $error("APB4 Slave port SEL implies that cpuif_wr_sel must be one-hot encoded");
+    `endif
+`endif
+{%- endif %}
+
+assign cpuif_req   = {{cpuif.signal("psel")}};
+assign cpuif_wr_en = {{cpuif.signal("pwrite")}};
+assign cpuif_rd_en = !{{cpuif.signal("pwrite")}};
+
+assign cpuif_wr_addr = {{cpuif.signal("paddr")}};
+assign cpuif_rd_addr = {{cpuif.signal("paddr")}};
+
+assign cpuif_wr_data = {{cpuif.signal("pwdata")}};
+assign cpuif_wr_byte_en = {{cpuif.signal("pstrb")}};
+
+assign {{cpuif.signal("prdata")}} = cpuif_rd_data;
+assign {{cpuif.signal("pready")}} = cpuif_rd_ack | cpuif_wr_ack;
+assign {{cpuif.signal("pslverr")}} = cpuif_rd_err | cpuif_wr_err;
+//--------------------------------------------------------------------------
+// Fanout CPU Bus interface signals
+//--------------------------------------------------------------------------
+{{fanout|walk(cpuif=cpuif)}}
+{%- if cpuif.is_interface %}
+
+//--------------------------------------------------------------------------
+// Intermediate signals for interface array fanin
+//--------------------------------------------------------------------------
+{{fanin_intermediate|walk(cpuif=cpuif)}}
+{%- endif %}
+
+//--------------------------------------------------------------------------
+// Fanin CPU Bus interface signals
+//--------------------------------------------------------------------------
+{{fanin|walk(cpuif=cpuif)}}

src/peakrdl_busdecoder/decode_logic_gen.py

@@ -63,11 +63,18 @@ class DecodeLogicGenerator(BusDecoderListener):
             l_bound_comp.append(f"({addr_width}'(i{i})*{SVInt(stride, addr_width)})")
             u_bound_comp.append(f"({addr_width}'(i{i})*{SVInt(stride, addr_width)})")
 
-        # Generate Conditions
-        return [
-            f"{self._flavor.cpuif_address} >= ({'+'.join(l_bound_comp)})",
-            f"{self._flavor.cpuif_address} < ({'+'.join(u_bound_comp)})",
-        ]
+        lower_expr = f"{self._flavor.cpuif_address} >= ({'+'.join(l_bound_comp)})"
+        upper_expr = f"{self._flavor.cpuif_address} < ({'+'.join(u_bound_comp)})"
+
+        predicates: list[str] = []
+        # Avoid generating a redundant >= 0 comparison, which triggers Verilator warnings.
+        if not (l_bound.value == 0 and len(l_bound_comp) == 1):
+            predicates.append(lower_expr)
+        # Avoid generating a redundant full-width < max comparison, which triggers Verilator warnings.
+        if not (u_bound.value == (1 << addr_width) and len(u_bound_comp) == 1):
+            predicates.append(upper_expr)
+
+        return predicates
 
     def cpuif_prot_predicate(self, node: AddressableNode) -> list[str]:
         if self._flavor == DecodeLogicFlavor.READ:
@@ -80,6 +87,20 @@ class DecodeLogicGenerator(BusDecoderListener):
     def enter_AddressableComponent(self, node: AddressableNode) -> WalkerAction | None:
         action = super().enter_AddressableComponent(node)
 
+        should_decode = action == WalkerAction.SkipDescendants
+
+        if not should_decode and self._ds.max_decode_depth == 0:
+            # When decoding all levels, treat leaf registers as decode boundary
+            for child in node.children():
+                if isinstance(child, AddressableNode):
+                    break
+            else:
+                should_decode = True
+
+        # Only generate select logic if we're at the decode boundary
+        if not should_decode:
+            return action
+
         conditions: list[str] = []
         conditions.extend(self.cpuif_addr_predicate(node))
         conditions.extend(self.cpuif_prot_predicate(node))
@@ -141,6 +162,8 @@ class DecodeLogicGenerator(BusDecoderListener):
     def __str__(self) -> str:
         body = self._decode_stack[-1]
         if isinstance(body, IfBody):
+            if len(body) == 0:
+                return f"{self._flavor.cpuif_select}.cpuif_err = 1'b1;"
             with body.cm(...) as b:
                 b += f"{self._flavor.cpuif_select}.cpuif_err = 1'b1;"
 

src/peakrdl_busdecoder/design_state.py

@@ -1,6 +1,6 @@
 from typing import TypedDict
 
-from systemrdl.node import AddrmapNode
+from systemrdl.node import AddressableNode, AddrmapNode
 from systemrdl.rdltypes.user_enum import UserEnum
 
 from .design_scanner import DesignScanner
@@ -14,6 +14,7 @@ class DesignStateKwargs(TypedDict, total=False):
     package_name: str
     address_width: int
     cpuif_unroll: bool
+    max_decode_depth: int
 
 
 class DesignState:
@@ -35,6 +36,7 @@ class DesignState:
         user_addr_width: int | None = kwargs.pop("address_width", None)
 
         self.cpuif_unroll: bool = kwargs.pop("cpuif_unroll", False)
+        self.max_decode_depth: int = kwargs.pop("max_decode_depth", 1)
 
         # ------------------------
         # Info about the design
@@ -70,3 +72,56 @@ class DesignState:
         if user_addr_width < self.addr_width:
             msg.fatal(f"User-specified address width shall be greater than or equal to {self.addr_width}.")
         self.addr_width = user_addr_width
+
+    def get_addressable_children_at_depth(self, unroll: bool = False) -> list[AddressableNode]:
+        """
+        Get addressable children at the decode boundary based on max_decode_depth.
+
+        max_decode_depth semantics:
+        - 0: decode all levels (return leaf registers)
+        - 1: decode only top level (return children at depth 1)
+        - 2: decode top + 1 level (return children at depth 2)
+        - N: decode down to depth N (return children at depth N)
+
+        Args:
+            unroll: Whether to unroll arrayed nodes
+
+        Returns:
+            List of addressable nodes at the decode boundary
+        """
+        from systemrdl.node import RegNode
+
+        def collect_nodes(node: AddressableNode, current_depth: int) -> list[AddressableNode]:
+            """Recursively collect nodes at the decode boundary."""
+            result: list[AddressableNode] = []
+
+            # For depth 0, collect all leaf registers
+            if self.max_decode_depth == 0:
+                # If this is a register, it's a leaf
+                if isinstance(node, RegNode):
+                    result.append(node)
+                else:
+                    # Recurse into children
+                    for child in node.children(unroll=unroll):
+                        if isinstance(child, AddressableNode):
+                            result.extend(collect_nodes(child, current_depth + 1))
+            else:
+                # For depth N, collect children at depth N
+                if current_depth == self.max_decode_depth:
+                    # We're at the decode boundary - return this node
+                    result.append(node)
+                elif current_depth < self.max_decode_depth:
+                    # We haven't reached the boundary yet - recurse
+                    for child in node.children(unroll=unroll):
+                        if isinstance(child, AddressableNode):
+                            result.extend(collect_nodes(child, current_depth + 1))
+
+            return result
+
+        # Start collecting from top node's children
+        nodes: list[AddressableNode] = []
+        for child in self.top_node.children(unroll=unroll):
+            if isinstance(child, AddressableNode):
+                nodes.extend(collect_nodes(child, 1))
+
+        return nodes

src/peakrdl_busdecoder/exporter.py

@@ -1,5 +1,4 @@
 import os
-from datetime import datetime
 from importlib.metadata import version
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, TypedDict
@@ -17,6 +16,7 @@ from .identifier_filter import kw_filter as kwf
 from .listener import BusDecoderListener
 from .struct_gen import StructGenerator
 from .sv_int import SVInt
+from .utils import clog2
 from .validate_design import DesignValidator
 
 
@@ -27,6 +27,7 @@ class ExporterKwargs(TypedDict, total=False):
     address_width: int
     cpuif_unroll: bool
     reuse_hwif_typedefs: bool
+    max_decode_depth: int
 
 
 if TYPE_CHECKING:
@@ -57,8 +58,9 @@ class BusDecoderExporter:
             loader=c_loader,
             undefined=jj.StrictUndefined,
         )
-        self.jj_env.filters["kwf"] = kwf  # type: ignore
-        self.jj_env.filters["walk"] = self.walk  # type: ignore
+        self.jj_env.filters["kwf"] = kwf
+        self.jj_env.filters["walk"] = self.walk
+        self.jj_env.filters["clog2"] = clog2
 
     def export(self, node: RootNode | AddrmapNode, output_dir: str, **kwargs: Unpack[ExporterKwargs]) -> None:
         """
@@ -84,6 +86,11 @@ class BusDecoderExporter:
         cpuif_unroll: bool
             Unroll arrayed addressable nodes into separate instances in the CPU
             interface. By default, arrayed nodes are kept as arrays.
+        max_decode_depth: int
+            Maximum depth for address decoder to descend into nested addressable
+            components. A value of 0 decodes all levels (infinite depth). A value
+            of 1 decodes only top-level children. A value of 2 decodes top-level
+            and one level deeper, etc. By default, the decoder descends 1 level deep.
         """
         # If it is the root node, skip to top addrmap
         if isinstance(node, RootNode):
@@ -91,7 +98,7 @@ class BusDecoderExporter:
         else:
             top_node = node
 
-        self.ds = DesignState(top_node, kwargs)
+        self.ds = DesignState(top_node, kwargs)  # ty: ignore
 
         cpuif_cls: type[BaseCpuif] = kwargs.pop("cpuif_cls", None) or APB4Cpuif
 
@@ -106,8 +113,7 @@ class BusDecoderExporter:
         DesignValidator(self).do_validate()
 
         # Build Jinja template context
-        context = {  # type: ignore
-            "current_date": datetime.now().strftime("%Y-%m-%d"),
+        context = {
             "version": version("peakrdl-busdecoder"),
             "cpuif": self.cpuif,
             "cpuif_decode": DecodeLogicGenerator,

src/peakrdl_busdecoder/listener.py

@@ -1,6 +1,6 @@
 from collections import deque
 
-from systemrdl.node import AddressableNode
+from systemrdl.node import AddressableNode, RegNode
 from systemrdl.walker import RDLListener, WalkerAction
 
 from .design_state import DesignState
@@ -12,15 +12,44 @@ class BusDecoderListener(RDLListener):
         self._ds = ds
         self._depth = 0
 
+    def should_skip_node(self, node: AddressableNode) -> bool:
+        """Check if this node should be skipped (not decoded)."""
+        # Check if current depth exceeds max depth
+        # max_decode_depth semantics:
+        # - 0 means decode all levels (infinite)
+        # - 1 means decode only top level (depth 0)
+        # - 2 means decode top + 1 level (depth 0 and 1)
+        # - N means decode down to depth N-1
+        if self._ds.max_decode_depth > 0 and self._depth >= self._ds.max_decode_depth:
+            return True
+
+        # Check if this node only contains external addressable children
+        if node != self._ds.top_node and not isinstance(node, RegNode):
+            if any(isinstance(c, AddressableNode) for c in node.children()) and all(
+                c.external for c in node.children() if isinstance(c, AddressableNode)
+            ):
+                return True
+
+        return False
+
     def enter_AddressableComponent(self, node: AddressableNode) -> WalkerAction | None:
         if node.array_dimensions:
             assert node.array_stride is not None, "Array stride should be defined for arrayed components"
-            self._array_stride_stack.extend(node.array_dimensions)
+            current_stride = node.array_stride
+            self._array_stride_stack.append(current_stride)
+
+            # Work backwards from rightmost to leftmost dimension (fastest to slowest changing)
+            # Each dimension's stride is the product of its size and the previous dimension's stride
+            for dim in node.array_dimensions[-1:0:-1]:
+                current_stride = current_stride * dim
+                self._array_stride_stack.appendleft(current_stride)
 
         self._depth += 1
 
-        if self._depth > 1:
+        # Check if we should skip this node's descendants
+        if self.should_skip_node(node):
             return WalkerAction.SkipDescendants
+
         return WalkerAction.Continue
 
     def exit_AddressableComponent(self, node: AddressableNode) -> None:

src/peakrdl_busdecoder/module_tmpl.sv

@@ -1,13 +1,11 @@
-
 //==========================================================
 //  Module: {{ds.module_name}}
 //  Description: CPU Interface Bus Decoder
-//  Author: PeakRDL-busdecoder
+//  Author: PeakRDL-BusDecoder
 //  License: LGPL-3.0
-//  Date: {{current_date}}
 //  Version: {{version}}
 //  Links:
-//    - https://github.com/arnavsacheti/PeakRDL-busdecoder
+//    - https://github.com/arnavsacheti/PeakRDL-BusDecoder
 //==========================================================
 
 
@@ -17,7 +15,6 @@ module {{ds.module_name}}
 ) {%- endif %} (
     {{cpuif.port_declaration|indent(4)}}
 );
-
     //--------------------------------------------------------------------------
     // CPU Bus interface logic
     //--------------------------------------------------------------------------
@@ -46,14 +43,14 @@ module {{ds.module_name}}
     //--------------------------------------------------------------------------
     // Slave <-> Internal CPUIF <-> Master
     //--------------------------------------------------------------------------
-    {{-cpuif.get_implementation()|indent(4)}}
+    {{cpuif.get_implementation()|indent(4)}}
 
     //--------------------------------------------------------------------------
     // Write Address Decoder
     //--------------------------------------------------------------------------
     always_comb begin
         // Default all write select signals to 0
-        cpuif_wr_sel = '0;
+        cpuif_wr_sel = '{default: '0};
 
         if (cpuif_req && cpuif_wr_en) begin
             // A write request is pending
@@ -68,7 +65,7 @@ module {{ds.module_name}}
     //--------------------------------------------------------------------------
     always_comb begin
         // Default all read select signals to 0
-        cpuif_rd_sel = '0;
+        cpuif_rd_sel = '{default: '0};
 
         if (cpuif_req && cpuif_rd_en) begin
             // A read request is pending

src/peakrdl_busdecoder/package_tmpl.sv

@@ -1,10 +1,20 @@
-// Generated by PeakRDL-busdecoder - A free and open-source SystemVerilog generator
-//  https://github.com/arnavsacheti/PeakRDL-busdecoder
+//==========================================================
+//  Package: {{ds.package_name}}
+//  Description: CPU Interface Bus Decoder Package
+//  Author: PeakRDL-BusDecoder
+//  License: LGPL-3.0
+//  Version: {{version}}
+//  Links:
+//    - https://github.com/arnavsacheti/PeakRDL-BusDecoder
+//==========================================================
+
 
 package {{ds.package_name}};
-
     localparam {{ds.module_name.upper()}}_DATA_WIDTH = {{ds.cpuif_data_width}};
     localparam {{ds.module_name.upper()}}_MIN_ADDR_WIDTH = {{ds.addr_width}};
     localparam {{ds.module_name.upper()}}_SIZE = {{SVInt(ds.top_node.size)}};
+{%- for child in cpuif.addressable_children %}
+    localparam {{ds.module_name.upper()}}_{{child.inst_name.upper()}}_ADDR_WIDTH = {{child.size|clog2}};
+{%- endfor %}
 endpackage
 {# (eof newline anchor) #}

src/peakrdl_busdecoder/struct_gen.py

@@ -3,7 +3,7 @@ from collections import deque
 from systemrdl.node import AddressableNode
 from systemrdl.walker import WalkerAction
 
-from .body import Body, StructBody
+from .body import StructBody
 from .design_state import DesignState
 from .identifier_filter import kw_filter as kwf
 from .listener import BusDecoderListener
@@ -16,42 +16,53 @@ class StructGenerator(BusDecoderListener):
     ) -> None:
         super().__init__(ds)
 
-        self._stack: deque[Body] = deque()
-        self._stack.append(StructBody("cpuif_sel_t", True, True))
+        self._stack: list[StructBody] = [StructBody("cpuif_sel_t", True, False)]
+        self._struct_defs: list[StructBody] = []
+        self._created_struct_stack: deque[bool] = deque()  # Track if we created a struct for each node
 
     def enter_AddressableComponent(self, node: AddressableNode) -> WalkerAction | None:
         action = super().enter_AddressableComponent(node)
 
-        self._skip = False
-        if action == WalkerAction.SkipDescendants:
-            self._skip = True
+        skip = action == WalkerAction.SkipDescendants
 
-        if node.children():
+        # Only create nested struct if we're not skipping and node has addressable children
+        has_addressable_children = any(isinstance(child, AddressableNode) for child in node.children())
+        if has_addressable_children and not skip:
             # Push new body onto stack
-            body = StructBody(f"cpuif_sel_{node.inst_name}_t", True, True)
+            body = StructBody(f"cpuif_sel_{node.inst_name}_t", True, False)
             self._stack.append(body)
+            self._created_struct_stack.append(True)
+        else:
+            self._created_struct_stack.append(False)
 
         return action
 
     def exit_AddressableComponent(self, node: AddressableNode) -> None:
         type = "logic"
 
-        if node.children():
+        # Pop the created_struct flag
+        created_struct = self._created_struct_stack.pop()
+
+        # Only pop struct body if we created one
+        if created_struct:
             body = self._stack.pop()
-            if body and isinstance(body, StructBody) and not self._skip:
-                self._stack.appendleft(body)
+            if body:
+                self._struct_defs.append(body)
                 type = body.name
 
         name = kwf(node.inst_name)
 
         if node.array_dimensions:
             for dim in node.array_dimensions:
-                name = f"[{dim - 1}:0]{name}"
+                name = f"{name}[{dim}]"
 
         self._stack[-1] += f"{type} {name};"
 
         super().exit_AddressableComponent(node)
 
     def __str__(self) -> str:
+        if "logic cpuif_err;" not in self._stack[-1].lines:
             self._stack[-1] += "logic cpuif_err;"
-        return "\n".join(map(str, self._stack))
+        bodies = [str(body) for body in self._struct_defs]
+        bodies.append(str(self._stack[-1]))
+        return "\n".join(bodies)

src/peakrdl_busdecoder/sv_int.py

@@ -1,3 +1,6 @@
+from typing import Literal
+
+
 class SVInt:
     def __init__(self, value: int, width: int | None = None) -> None:
         self.value = value
@@ -19,3 +22,27 @@ class SVInt:
             return SVInt(self.value + other.value, max(self.width, other.width))
         else:
             return SVInt(self.value + other.value, None)
+
+    def __sub__(self, other: "SVInt") -> "SVInt":
+        if self.width is not None and other.width is not None:
+            return SVInt(self.value - other.value, max(self.width, other.width))
+        else:
+            return SVInt(self.value - other.value, None)
+
+    def __len__(self) -> int:
+        if self.width is not None:
+            return self.width
+        else:
+            return self.value.bit_length()
+
+    def to_bytes(self, byteorder: Literal["little", "big"] = "little") -> bytes:
+        byte_length = (self.value.bit_length() + 7) // 8
+        return self.value.to_bytes(byte_length, byteorder)
+
+    def __eq__(self, other: object) -> bool:
+        if not isinstance(other, SVInt):
+            return NotImplemented
+        return self.value == other.value and self.width == other.width
+
+    def __hash__(self) -> int:
+        return hash((self.value, self.width))

src/peakrdl_busdecoder/utils.py

@@ -62,7 +62,6 @@ def ref_is_internal(top_node: AddrmapNode, ref: Node | PropertyReference) -> boo
     else:
         current_node = ref
 
-    # pyrefly: ignore[bad-assignment] - false positive due to circular type checking
     while current_node is not None:
         if current_node == top_node:
             # reached top node without finding any external components

src/peakrdl_busdecoder/validate_design.py

@@ -4,7 +4,7 @@ from systemrdl.node import AddressableNode, AddrmapNode, FieldNode, Node, Regfil
 from systemrdl.rdltypes.references import PropertyReference
 from systemrdl.walker import RDLListener, RDLWalker, WalkerAction
 
-from .utils import is_pow2, ref_is_internal, roundup_pow2
+from .utils import ref_is_internal
 
 if TYPE_CHECKING:
     from .exporter import BusDecoderExporter
@@ -74,7 +74,9 @@ class DesignValidator(RDLListener):
                 f"instance '{node.inst_name}' must be a multiple of {alignment}",
                 node.inst.inst_src_ref,
             )
-        if node.is_array and (node.array_stride % alignment) != 0:  # type: ignore # is_array implies stride is not none
+        if node.is_array and (
+            node.array_stride is not None and (node.array_stride % alignment) != 0
+        ):  # is_array implies stride is not none
             self.msg.error(
                 "Unaligned registers are not supported. Address stride of "
                 f"instance array '{node.inst_name}' must be a multiple of {alignment}",
@@ -159,27 +161,3 @@ class DesignValidator(RDLListener):
             else:
                 # Exiting top addrmap. Resolve final answer
                 self.contains_external_block = contains_external_block
-
-            if contains_external_block:
-                # Check that addressing follows strict alignment rules to allow
-                # for simplified address bit-pruning
-                if node.external:
-                    err_suffix = "is external"
-                else:
-                    err_suffix = "contains an external addrmap/regfile/mem"
-
-                req_align = roundup_pow2(node.size)
-                if (node.raw_address_offset % req_align) != 0:
-                    self.msg.error(
-                        f"Address offset +0x{node.raw_address_offset:x} of instance '{node.inst_name}' is not a power of 2 multiple of its size 0x{node.size:x}. "
-                        f"This is required by the busdecoder exporter if a component {err_suffix}.",
-                        node.inst.inst_src_ref,
-                    )
-                if node.is_array:
-                    assert node.array_stride is not None
-                    if not is_pow2(node.array_stride):
-                        self.msg.error(
-                            f"Address stride of instance array '{node.inst_name}' is not a power of 2"
-                            f"This is required by the busdecoder exporter if a component {err_suffix}.",
-                            node.inst.inst_src_ref,
-                        )

tests/README.md

@@ -1,19 +1,27 @@
-# Unit tests
+# Tests
 
-The bus decoder exporter now ships with a small unit test suite built around
-`pytest`. The tests exercise the Python implementation directly and use the
-[`systemrdl-compiler`](https://github.com/SystemRDL/systemrdl-compiler)
+The bus decoder exporter includes comprehensive test suites to validate both the
+Python implementation and the generated SystemVerilog RTL.
+
+## Unit Tests
+
+The unit test suite is built around `pytest` and exercises the Python implementation
+directly using the [`systemrdl-compiler`](https://github.com/SystemRDL/systemrdl-compiler)
 package to elaborate inline SystemRDL snippets.
 
-## Install dependencies
+### Install dependencies
 
 Create an isolated environment if desired and install the minimal requirements:
 
 ```bash
-python -m pip install -r tests/requirements.txt
+# Using uv (recommended)
+uv sync --group test
+
+# Or using pip
+python -m pip install -e . parameterized pytest pytest-cov pytest-xdist
 ```
 
-## Running the suite
+### Running the suite
 
 Invoke `pytest` from the repository root (or the `tests` directory) and point it
 at the unit tests:
@@ -25,3 +33,67 @@ pytest tests/unit
 Pytest will automatically discover tests that follow the `test_*.py` naming
 pattern and can make use of the `compile_rdl` fixture defined in
 `tests/unit/conftest.py` to compile inline SystemRDL sources.
+
+## Cocotb Integration Tests
+
+The cocotb test suite validates the functionality of generated SystemVerilog RTL
+through simulation. These tests generate bus decoders for different CPU interfaces
+(APB3, APB4, AXI4-Lite) and verify that read/write operations work correctly.
+
+### Install dependencies
+
+```bash
+# Install with cocotb support using uv (recommended)
+uv sync --group test
+
+# Or using pip
+python -m pip install -e . parameterized pytest pytest-cov pytest-xdist cocotb cocotb-bus
+
+# Install HDL simulator (choose one)
+apt-get install iverilog  # Icarus Verilog
+apt-get install verilator # Verilator
+```
+
+### Running the tests
+
+#### Integration tests (no simulator required)
+
+These tests validate code generation without requiring an HDL simulator:
+
+```bash
+pytest tests/cocotb/testbenches/test_integration.py -v
+```
+
+#### Example code generation
+
+Run examples to see generated code for different configurations:
+
+```bash
+python tests/cocotb/examples.py
+```
+
+#### Simulation layout
+
+Simulation-oriented tests are grouped by CPU interface under
+`tests/cocotb/<cpuif>/<group>/`. For example, the APB4 smoke test lives in
+`tests/cocotb/apb4/smoke/` alongside its pytest runner module. Each runner
+compiles the appropriate SystemRDL design, adds the interface wrapper from
+`hdl-src/`, and invokes cocotb via Verilator.
+
+#### Full simulation tests (requires simulator)
+
+To execute the smoke tests for every supported interface:
+
+```bash
+pytest tests/cocotb/*/smoke/test_runner.py -v
+```
+
+To target a single interface, point pytest at that runner module:
+
+```bash
+pytest tests/cocotb/apb3/smoke/test_runner.py -v
+pytest tests/cocotb/apb4/smoke/test_runner.py -v
+pytest tests/cocotb/axi4lite/smoke/test_runner.py -v
+```
+
+For more information about cocotb tests, see [`tests/cocotb/README.md`](cocotb/README.md).

tests/body/test_body.py

@@ -0,0 +1,47 @@
+from peakrdl_busdecoder.body import Body
+
+
+class TestBody:
+    """Test the base Body class."""
+
+    def test_empty_body(self) -> None:
+        """Test empty body returns empty string."""
+        body = Body()
+        assert str(body) == ""
+        assert not body  # Should be falsy when empty
+
+    def test_add_single_line(self) -> None:
+        """Test adding a single line to body."""
+        body = Body()
+        body += "line1"
+        assert str(body) == "line1"
+        assert body  # Should be truthy when not empty
+
+    def test_add_multiple_lines(self) -> None:
+        """Test adding multiple lines to body."""
+        body = Body()
+        body += "line1"
+        body += "line2"
+        body += "line3"
+        expected = "line1\nline2\nline3"
+        assert str(body) == expected
+
+    def test_add_returns_self(self) -> None:
+        """Test that add operation returns self for chaining."""
+        body = Body()
+        body += "line1"
+        body += "line2"
+        # Chaining works because += returns self
+        assert len(body.lines) == 2
+
+    def test_add_nested_body(self) -> None:
+        """Test adding another body as a line."""
+        outer = Body()
+        inner = Body()
+        inner += "inner1"
+        inner += "inner2"
+        outer += "outer1"
+        outer += inner
+        outer += "outer2"
+        expected = "outer1\ninner1\ninner2\nouter2"
+        assert str(outer) == expected

tests/body/test_combinational_body.py

@@ -0,0 +1,39 @@
+from peakrdl_busdecoder.body import CombinationalBody, IfBody
+
+
+class TestCombinationalBody:
+    """Test the CombinationalBody class."""
+
+    def test_simple_combinational_block(self) -> None:
+        """Test simple combinational block."""
+        body = CombinationalBody()
+        body += "assign1 = value1;"
+        body += "assign2 = value2;"
+
+        result = str(body)
+        assert "always_comb" in result
+        assert "begin" in result
+        assert "assign1 = value1;" in result
+        assert "assign2 = value2;" in result
+        assert "end" in result
+
+    def test_empty_combinational_block(self) -> None:
+        """Test empty combinational block."""
+        body = CombinationalBody()
+        result = str(body)
+        assert "always_comb" in result
+        assert "begin" in result
+        assert "end" in result
+
+    def test_combinational_with_if_statement(self) -> None:
+        """Test combinational block with if statement."""
+        cb = CombinationalBody()
+        ifb = IfBody()
+        with ifb.cm("condition") as b:
+            b += "assignment = value;"
+        cb += ifb
+
+        result = str(cb)
+        assert "always_comb" in result
+        assert "if (condition)" in result
+        assert "assignment = value;" in result

tests/body/test_for_loop_body.py

@@ -0,0 +1,46 @@
+from peakrdl_busdecoder.body import ForLoopBody
+
+
+class TestForLoopBody:
+    """Test the ForLoopBody class."""
+
+    def test_genvar_for_loop(self) -> None:
+        """Test genvar-style for loop."""
+        body = ForLoopBody("genvar", "i", 4)
+        body += "statement1;"
+        body += "statement2;"
+
+        result = str(body)
+        assert "for (genvar i = 0; i < 4; i++)" in result
+        assert "statement1;" in result
+        assert "statement2;" in result
+        assert "end" in result
+
+    def test_int_for_loop(self) -> None:
+        """Test int-style for loop."""
+        body = ForLoopBody("int", "j", 8)
+        body += "assignment = value;"
+
+        result = str(body)
+        assert "for (int j = 0; j < 8; j++)" in result
+        assert "assignment = value;" in result
+        assert "end" in result
+
+    def test_empty_for_loop(self) -> None:
+        """Test empty for loop."""
+        body = ForLoopBody("genvar", "k", 2)
+        result = str(body)
+        # Empty for loop should still have structure
+        assert "for (genvar k = 0; k < 2; k++)" in result
+
+    def test_nested_for_loops(self) -> None:
+        """Test nested for loops."""
+        outer = ForLoopBody("genvar", "i", 3)
+        inner = ForLoopBody("genvar", "j", 2)
+        inner += "nested_statement;"
+        outer += inner
+
+        result = str(outer)
+        assert "for (genvar i = 0; i < 3; i++)" in result
+        assert "for (genvar j = 0; j < 2; j++)" in result
+        assert "nested_statement;" in result

tests/body/test_if_body.py

@@ -0,0 +1,86 @@
+from peakrdl_busdecoder.body import IfBody
+
+
+class TestIfBody:
+    """Test the IfBody class."""
+
+    def test_simple_if(self):
+        """Test simple if statement."""
+        body = IfBody()
+        with body.cm("condition1") as b:
+            b += "statement1;"
+
+        result = str(body)
+        assert "if (condition1)" in result
+        assert "statement1;" in result
+        assert "end" in result
+
+    def test_if_else(self):
+        """Test if-else statement."""
+        body = IfBody()
+        with body.cm("condition1") as b:
+            b += "if_statement;"
+        with body.cm(None) as b:  # None for else
+            b += "else_statement;"
+
+        result = str(body)
+        assert "if (condition1)" in result
+        assert "if_statement;" in result
+        assert "else" in result
+        assert "else_statement;" in result
+
+    def test_if_elif_else(self):
+        """Test if-elif-else chain."""
+        body = IfBody()
+        with body.cm("condition1") as b:
+            b += "statement1;"
+        with body.cm("condition2") as b:
+            b += "statement2;"
+        with body.cm(None) as b:  # None for else
+            b += "statement3;"
+
+        result = str(body)
+        assert "if (condition1)" in result
+        assert "statement1;" in result
+        assert "else if (condition2)" in result
+        assert "statement2;" in result
+        assert "else" in result
+        assert "statement3;" in result
+
+    def test_multiple_elif(self):
+        """Test multiple elif statements."""
+        body = IfBody()
+        with body.cm("cond1") as b:
+            b += "stmt1;"
+        with body.cm("cond2") as b:
+            b += "stmt2;"
+        with body.cm("cond3") as b:
+            b += "stmt3;"
+
+        result = str(body)
+        assert "if (cond1)" in result
+        assert "else if (cond2)" in result
+        assert "else if (cond3)" in result
+
+    def test_empty_if_branches(self):
+        """Test if statement with empty branches."""
+        body = IfBody()
+        with body.cm("condition"):
+            pass
+
+        result = str(body)
+        assert "if (condition)" in result
+
+    def test_nested_if(self):
+        """Test nested if statements."""
+        outer = IfBody()
+        with outer.cm("outer_cond") as outer_body:
+            inner = IfBody()
+            with inner.cm("inner_cond") as inner_body:
+                inner_body += "nested_statement;"
+            outer_body += inner
+
+        result = str(outer)
+        assert "if (outer_cond)" in result
+        assert "if (inner_cond)" in result
+        assert "nested_statement;" in result

tests/body/test_struct_body.py

@@ -0,0 +1,59 @@
+from peakrdl_busdecoder.body import StructBody
+
+
+class TestStructBody:
+    """Test the StructBody class."""
+
+    def test_simple_struct(self) -> None:
+        """Test simple struct definition."""
+        body = StructBody("my_struct_t", packed=True, typedef=True)
+        body += "logic [7:0] field1;"
+        body += "logic field2;"
+
+        result = str(body)
+        assert "typedef struct packed" in result
+        assert "my_struct_t" in result
+        assert "logic [7:0] field1;" in result
+        assert "logic field2;" in result
+
+    def test_unpacked_struct(self) -> None:
+        """Test unpacked struct definition."""
+        body = StructBody("unpacked_t", packed=False, typedef=True)
+        body += "int field1;"
+
+        result = str(body)
+        assert "typedef struct" in result
+        assert "packed" not in result or "typedef struct {" in result
+        assert "unpacked_t" in result
+
+    def test_struct_without_typedef(self) -> None:
+        """Test struct without typedef."""
+        body = StructBody("my_struct", packed=True, typedef=False)
+        body += "logic field;"
+
+        result = str(body)
+        # When typedef=False, packed is not used
+        assert "struct {" in result
+        assert "typedef" not in result
+        assert "my_struct" in result
+
+    def test_empty_struct(self) -> None:
+        """Test empty struct."""
+        body = StructBody("empty_t", packed=True, typedef=True)
+        result = str(body)
+        assert "typedef struct packed" in result
+        assert "empty_t" in result
+
+    def test_nested_struct(self) -> None:
+        """Test struct with nested struct."""
+        outer = StructBody("outer_t", packed=True, typedef=True)
+        inner = StructBody("inner_t", packed=True, typedef=True)
+        inner += "logic field1;"
+        outer += "logic field2;"
+        outer += str(inner)  # Include inner struct as a string
+
+        result = str(outer)
+        assert "outer_t" in result
+        assert "field2;" in result
+        # Inner struct should appear in the string
+        assert "inner_t" in result

tests/cocotb/apb3/smoke/test_register_access.py

@@ -0,0 +1,310 @@
+"""APB3 smoke tests generated from SystemRDL sources."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import cocotb
+from cocotb.triggers import RisingEdge, Timer
+
+from tests.cocotb_lib.handle_utils import SignalHandle
+from tests.cocotb_lib.protocol_utils import (
+    all_index_pairs,
+    find_invalid_address,
+    get_int,
+    load_config,
+    set_value,
+    start_clock,
+)
+
+
+class _Apb3SlaveShim:
+    """Accessor for the APB3 slave signals on the DUT."""
+
+    def __init__(self, dut):
+        prefix = "s_apb"
+        self.PCLK = getattr(dut, f"{prefix}_PCLK", None)
+        self.PRESETn = getattr(dut, f"{prefix}_PRESETn", None)
+        self.PSEL = getattr(dut, f"{prefix}_PSEL")
+        self.PENABLE = getattr(dut, f"{prefix}_PENABLE")
+        self.PWRITE = getattr(dut, f"{prefix}_PWRITE")
+        self.PADDR = getattr(dut, f"{prefix}_PADDR")
+        self.PWDATA = getattr(dut, f"{prefix}_PWDATA")
+        self.PRDATA = getattr(dut, f"{prefix}_PRDATA")
+        self.PREADY = getattr(dut, f"{prefix}_PREADY")
+        self.PSLVERR = getattr(dut, f"{prefix}_PSLVERR")
+
+
+def _build_master_table(dut, masters_cfg: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
+    table: dict[str, dict[str, Any]] = {}
+    for master in masters_cfg:
+        prefix = master["port_prefix"]
+        entry = {
+            "indices": [tuple(idx) for idx in master["indices"]] or [tuple()],
+            "outputs": {
+                "PSEL": SignalHandle(dut, f"{prefix}_PSEL"),
+                "PENABLE": SignalHandle(dut, f"{prefix}_PENABLE"),
+                "PWRITE": SignalHandle(dut, f"{prefix}_PWRITE"),
+                "PADDR": SignalHandle(dut, f"{prefix}_PADDR"),
+                "PWDATA": SignalHandle(dut, f"{prefix}_PWDATA"),
+            },
+            "inputs": {
+                "PRDATA": SignalHandle(dut, f"{prefix}_PRDATA"),
+                "PREADY": SignalHandle(dut, f"{prefix}_PREADY"),
+                "PSLVERR": SignalHandle(dut, f"{prefix}_PSLVERR"),
+            },
+            "inst_size": master["inst_size"],
+            "inst_address": master["inst_address"],
+        }
+        table[master["inst_name"]] = entry
+    return table
+
+
+def _write_pattern(address: int, width: int) -> int:
+    mask = (1 << width) - 1
+    return ((address * 0x2041) ^ 0xCAFEBABE) & mask
+
+
+def _read_pattern(address: int, width: int) -> int:
+    mask = (1 << width) - 1
+    return ((address ^ 0x0BAD_F00D) + width) & mask
+
+
+@cocotb.test()
+async def test_apb3_address_decoding(dut) -> None:
+    """Exercise the APB3 slave interface against sampled register addresses."""
+    config = load_config()
+    slave = _Apb3SlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    await start_clock(slave.PCLK)
+    if slave.PRESETn is not None:
+        slave.PRESETn.value = 1
+
+    slave.PSEL.value = 0
+    slave.PENABLE.value = 0
+    slave.PWRITE.value = 0
+    slave.PADDR.value = 0
+    slave.PWDATA.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["PRDATA"], idx, 0)
+        set_value(entry["inputs"]["PREADY"], idx, 0)
+        set_value(entry["inputs"]["PSLVERR"], idx, 0)
+
+    if slave.PCLK is not None:
+        await RisingEdge(slave.PCLK)
+    else:
+        await Timer(1, unit="ns")
+
+    addr_mask = (1 << config["address_width"]) - 1
+
+    for txn in config["transactions"]:
+        master_name = txn["master"]
+        index = tuple(txn["index"])
+        entry = masters[master_name]
+
+        address = txn["address"] & addr_mask
+        write_data = _write_pattern(address, config["data_width"])
+
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        set_value(entry["inputs"]["PSLVERR"], index, 0)
+
+        # ------------------------------------------------------------------
+        # Setup phase
+        # ------------------------------------------------------------------
+        slave.PADDR.value = address
+        slave.PWDATA.value = write_data
+        slave.PWRITE.value = 1
+        slave.PSEL.value = 1
+        slave.PENABLE.value = 0
+
+        dut._log.info(
+            f"Starting transaction {txn['label']} to {master_name}{index} at address 0x{address:08X}"
+        )
+        master_address = (address - entry["inst_address"]) % entry["inst_size"]
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} should assert PSEL for write"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 0, (
+            f"{master_name} must hold PENABLE low in setup"
+        )
+        assert get_int(entry["outputs"]["PWRITE"], index) == 1, f"{master_name} should see write direction"
+        assert get_int(entry["outputs"]["PADDR"], index) == master_address, (
+            f"{master_name} must receive write address"
+        )
+        assert get_int(entry["outputs"]["PWDATA"], index) == write_data, (
+            f"{master_name} must receive write data"
+        )
+
+        for other_name, other_idx in all_index_pairs(masters):
+            if other_name == master_name and other_idx == index:
+                continue
+            other_entry = masters[other_name]
+            assert get_int(other_entry["outputs"]["PSEL"], other_idx) == 0, (
+                f"{other_name}{other_idx} should remain idle during {txn['label']}"
+            )
+
+        # ------------------------------------------------------------------
+        # Access phase
+        # ------------------------------------------------------------------
+        set_value(entry["inputs"]["PREADY"], index, 1)
+        slave.PENABLE.value = 1
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} must keep PSEL asserted"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 1, (
+            f"{master_name} must assert PENABLE in access"
+        )
+        assert get_int(entry["outputs"]["PADDR"], index) == master_address, (
+            f"{master_name} must keep write address stable"
+        )
+        assert get_int(entry["outputs"]["PWDATA"], index) == write_data, (
+            f"{master_name} must keep write data stable"
+        )
+
+        assert int(slave.PREADY.value) == 1, "Slave ready should mirror selected master"
+        assert int(slave.PSLVERR.value) == 0, "Write should complete without error"
+
+        slave.PSEL.value = 0
+        slave.PENABLE.value = 0
+        slave.PWRITE.value = 0
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        # ------------------------------------------------------------------
+        # Read phase
+        # ------------------------------------------------------------------
+        read_data = _read_pattern(address, config["data_width"])
+        set_value(entry["inputs"]["PRDATA"], index, read_data)
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        set_value(entry["inputs"]["PSLVERR"], index, 0)
+
+        # ------------------------------------------------------------------
+        # Setup phase
+        # ------------------------------------------------------------------
+        slave.PADDR.value = address
+        slave.PWRITE.value = 0
+        slave.PSEL.value = 1
+        slave.PENABLE.value = 0
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} must assert PSEL for read"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 0, (
+            f"{master_name} must hold PENABLE low in setup"
+        )
+        assert get_int(entry["outputs"]["PWRITE"], index) == 0, (
+            f"{master_name} should clear write during read"
+        )
+        assert get_int(entry["outputs"]["PADDR"], index) == master_address, (
+            f"{master_name} must receive read address"
+        )
+
+        for other_name, other_idx in all_index_pairs(masters):
+            if other_name == master_name and other_idx == index:
+                continue
+            other_entry = masters[other_name]
+            assert get_int(other_entry["outputs"]["PSEL"], other_idx) == 0, (
+                f"{other_name}{other_idx} must stay idle during read of {txn['label']}"
+            )
+
+        # ------------------------------------------------------------------
+        # Access phase
+        # ------------------------------------------------------------------
+        set_value(entry["inputs"]["PREADY"], index, 1)
+        slave.PENABLE.value = 1
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} must keep PSEL asserted"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 1, (
+            f"{master_name} must assert PENABLE in access"
+        )
+
+        assert int(slave.PRDATA.value) == read_data, "Read data should propagate back to the slave"
+        assert int(slave.PREADY.value) == 1, "Slave ready should acknowledge the read"
+        assert int(slave.PSLVERR.value) == 0, "Read should not signal an error"
+
+        slave.PSEL.value = 0
+        slave.PENABLE.value = 0
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        set_value(entry["inputs"]["PRDATA"], index, 0)
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+
+@cocotb.test()
+async def test_apb3_invalid_address_response(dut) -> None:
+    """Ensure invalid addresses yield an error response and no master select."""
+    config = load_config()
+    slave = _Apb3SlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    await start_clock(slave.PCLK)
+    if slave.PRESETn is not None:
+        slave.PRESETn.value = 1
+
+    slave.PSEL.value = 0
+    slave.PENABLE.value = 0
+    slave.PWRITE.value = 0
+    slave.PADDR.value = 0
+    slave.PWDATA.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["PREADY"], idx, 0)
+        set_value(entry["inputs"]["PSLVERR"], idx, 0)
+        set_value(entry["inputs"]["PRDATA"], idx, 0)
+
+    invalid_addr = find_invalid_address(config)
+    if invalid_addr is None:
+        dut._log.warning("No unmapped address found; skipping invalid address test")
+        return
+
+    slave.PADDR.value = invalid_addr
+    slave.PWRITE.value = 1
+    slave.PWDATA.value = _write_pattern(invalid_addr, config["data_width"])
+    slave.PSEL.value = 1
+    slave.PENABLE.value = 0
+
+    if slave.PCLK is not None:
+        await RisingEdge(slave.PCLK)
+    else:
+        await Timer(1, unit="ns")
+
+    slave.PENABLE.value = 1
+
+    if slave.PCLK is not None:
+        await RisingEdge(slave.PCLK)
+    else:
+        await Timer(1, unit="ns")
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        assert get_int(entry["outputs"]["PSEL"], idx) == 0, (
+            f"{master_name}{idx} must stay idle for invalid address"
+        )
+
+    assert int(slave.PREADY.value) == 1, "Invalid address should still complete the transfer"
+    assert int(slave.PSLVERR.value) == 1, "Invalid address should raise PSLVERR"

tests/cocotb/apb3/smoke/test_runner.py

@@ -0,0 +1,86 @@
+"""Pytest wrapper launching the APB3 cocotb smoke tests."""
+
+from __future__ import annotations
+
+import json
+import logging
+from pathlib import Path
+
+import pytest
+
+from peakrdl_busdecoder.cpuif.apb3.apb3_cpuif_flat import APB3CpuifFlat
+
+try:  # pragma: no cover - optional dependency shim
+    from cocotb.runner import get_runner
+except ImportError:  # pragma: no cover
+    from cocotb_tools.runner import get_runner
+
+from tests.cocotb_lib import RDL_CASES
+from tests.cocotb_lib.utils import colorize_cocotb_log, get_verilog_sources, prepare_cpuif_case
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+@pytest.mark.parametrize(("rdl_file", "top_name"), RDL_CASES, ids=[case[1] for case in RDL_CASES])
+def test_apb3_smoke(tmp_path: Path, rdl_file: str, top_name: str) -> None:
+    """Compile each APB3 design variant and execute the cocotb smoke test."""
+    repo_root = Path(__file__).resolve().parents[4]
+    rdl_path = repo_root / "tests" / "cocotb_lib" / "rdl" / rdl_file
+    build_root = tmp_path / top_name
+
+    module_path, package_path, config = prepare_cpuif_case(
+        str(rdl_path),
+        top_name,
+        build_root,
+        cpuif_cls=APB3CpuifFlat,
+        control_signal="PSEL",
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb3_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    sim_build = build_root / "sim_build"
+
+    build_log_file = build_root / "build.log"
+    sim_log_file = build_root / "simulation.log"
+
+    try:
+        runner.build(
+            sources=sources,
+            hdl_toplevel=module_path.stem,
+            build_dir=sim_build,
+            log_file=str(build_log_file),
+        )
+    except SystemExit as e:
+        # Print build log on failure for easier debugging
+        if build_log_file.exists():
+            logging.error(f"""
+=== Build Log ===
+{colorize_cocotb_log(build_log_file.read_text())}
+=== End Build Log ===
+""")
+        if e.code != 0:
+            raise
+
+    try:
+        runner.test(
+            hdl_toplevel=module_path.stem,
+            test_module="tests.cocotb.apb3.smoke.test_register_access",
+            build_dir=sim_build,
+            log_file=str(sim_log_file),
+            extra_env={"RDL_TEST_CONFIG": json.dumps(config)},
+        )
+    except SystemExit as e:
+        # Print simulation log on failure for easier debugging
+        if sim_log_file.exists():
+            logging.error(f"""
+=== Simulation Log ===
+{colorize_cocotb_log(sim_log_file.read_text())}
+=== End Simulation Log ===
+""")
+        if e.code != 0:
+            raise

tests/cocotb/apb3/smoke/test_variable_depth.py

@@ -0,0 +1,183 @@
+"""APB3 smoke tests for variable depth design testing max_decode_depth parameter."""
+
+import cocotb
+from cocotb.triggers import Timer
+
+from tests.cocotb_lib.protocol_utils import apb_access, apb_setup
+
+
+class _Apb3SlaveShim:
+    def __init__(self, dut):
+        prefix = "s_apb"
+        self.PSEL = getattr(dut, f"{prefix}_PSEL")
+        self.PENABLE = getattr(dut, f"{prefix}_PENABLE")
+        self.PWRITE = getattr(dut, f"{prefix}_PWRITE")
+        self.PADDR = getattr(dut, f"{prefix}_PADDR")
+        self.PWDATA = getattr(dut, f"{prefix}_PWDATA")
+        self.PRDATA = getattr(dut, f"{prefix}_PRDATA")
+        self.PREADY = getattr(dut, f"{prefix}_PREADY")
+        self.PSLVERR = getattr(dut, f"{prefix}_PSLVERR")
+
+
+class _Apb3MasterShim:
+    def __init__(self, dut, base: str):
+        self.PSEL = getattr(dut, f"{base}_PSEL")
+        self.PENABLE = getattr(dut, f"{base}_PENABLE")
+        self.PWRITE = getattr(dut, f"{base}_PWRITE")
+        self.PADDR = getattr(dut, f"{base}_PADDR")
+        self.PWDATA = getattr(dut, f"{base}_PWDATA")
+        self.PRDATA = getattr(dut, f"{base}_PRDATA")
+        self.PREADY = getattr(dut, f"{base}_PREADY")
+        self.PSLVERR = getattr(dut, f"{base}_PSLVERR")
+
+
+def _apb3_slave(dut):
+    return getattr(dut, "s_apb", None) or _Apb3SlaveShim(dut)
+
+
+def _apb3_master(dut, base: str):
+    return getattr(dut, base, None) or _Apb3MasterShim(dut, base)
+
+
+@cocotb.test()
+async def test_depth_1(dut):
+    """Test max_decode_depth=1 - should have interface for inner1 only."""
+    s_apb = _apb3_slave(dut)
+
+    # At depth 1, we should have m_apb_inner1 but not deeper interfaces
+    inner1 = _apb3_master(dut, "m_apb_inner1")
+
+    # Default slave side inputs
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    s_apb.PWRITE.value = 0
+    s_apb.PADDR.value = 0
+    s_apb.PWDATA.value = 0
+
+    inner1.PRDATA.value = 0
+    inner1.PREADY.value = 0
+    inner1.PSLVERR.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select inner1)
+    inner1.PREADY.value = 1
+    await apb_setup(s_apb, 0x0, True, 0x12345678)
+    await apb_access(s_apb)
+
+    assert int(inner1.PSEL.value) == 1, "inner1 must be selected"
+    assert int(inner1.PWRITE.value) == 1, "Write should propagate"
+    assert int(s_apb.PREADY.value) == 1, "Ready should mirror master"
+
+
+@cocotb.test()
+async def test_depth_2(dut):
+    """Test max_decode_depth=2 - should have interfaces for reg1 and inner2."""
+    s_apb = _apb3_slave(dut)
+
+    # At depth 2, we should have m_apb_reg1 and m_apb_inner2
+    reg1 = _apb3_master(dut, "m_apb_reg1")
+    inner2 = _apb3_master(dut, "m_apb_inner2")
+
+    # Default slave side inputs
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    s_apb.PWRITE.value = 0
+    s_apb.PADDR.value = 0
+    s_apb.PWDATA.value = 0
+
+    reg1.PRDATA.value = 0
+    reg1.PREADY.value = 0
+    reg1.PSLVERR.value = 0
+
+    inner2.PRDATA.value = 0
+    inner2.PREADY.value = 0
+    inner2.PSLVERR.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select reg1)
+    reg1.PREADY.value = 1
+    await apb_setup(s_apb, 0x0, True, 0xABCDEF01)
+    await apb_access(s_apb)
+
+    assert int(reg1.PSEL.value) == 1, "reg1 must be selected for address 0x0"
+    assert int(inner2.PSEL.value) == 0, "inner2 should not be selected"
+
+    # Reset
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    reg1.PREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x10 (should select inner2)
+    inner2.PREADY.value = 1
+    await apb_setup(s_apb, 0x10, True, 0x23456789)
+    await apb_access(s_apb)
+
+    assert int(inner2.PSEL.value) == 1, "inner2 must be selected for address 0x10"
+    assert int(reg1.PSEL.value) == 0, "reg1 should not be selected"
+
+
+@cocotb.test()
+async def test_depth_0(dut):
+    """Test max_decode_depth=0 - should have interfaces for all leaf registers."""
+    s_apb = _apb3_slave(dut)
+
+    # At depth 0, we should have all leaf registers: reg1, reg2, reg2b
+    reg1 = _apb3_master(dut, "m_apb_reg1")
+    reg2 = _apb3_master(dut, "m_apb_reg2")
+    reg2b = _apb3_master(dut, "m_apb_reg2b")
+
+    # Default slave side inputs
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    s_apb.PWRITE.value = 0
+    s_apb.PADDR.value = 0
+    s_apb.PWDATA.value = 0
+
+    for master in [reg1, reg2, reg2b]:
+        master.PRDATA.value = 0
+        master.PREADY.value = 0
+        master.PSLVERR.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select reg1)
+    reg1.PREADY.value = 1
+    await apb_setup(s_apb, 0x0, True, 0x11111111)
+    await apb_access(s_apb)
+
+    assert int(reg1.PSEL.value) == 1, "reg1 must be selected for address 0x0"
+    assert int(reg2.PSEL.value) == 0, "reg2 should not be selected"
+    assert int(reg2b.PSEL.value) == 0, "reg2b should not be selected"
+
+    # Reset
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    reg1.PREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x10 (should select reg2)
+    reg2.PREADY.value = 1
+    await apb_setup(s_apb, 0x10, True, 0x22222222)
+    await apb_access(s_apb)
+
+    assert int(reg2.PSEL.value) == 1, "reg2 must be selected for address 0x10"
+    assert int(reg1.PSEL.value) == 0, "reg1 should not be selected"
+    assert int(reg2b.PSEL.value) == 0, "reg2b should not be selected"
+
+    # Reset
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    reg2.PREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x14 (should select reg2b)
+    reg2b.PREADY.value = 1
+    await apb_setup(s_apb, 0x14, True, 0x33333333)
+    await apb_access(s_apb)
+
+    assert int(reg2b.PSEL.value) == 1, "reg2b must be selected for address 0x14"
+    assert int(reg1.PSEL.value) == 0, "reg1 should not be selected"
+    assert int(reg2.PSEL.value) == 0, "reg2 should not be selected"

tests/cocotb/apb3/smoke/test_variable_depth_runner.py

@@ -0,0 +1,128 @@
+"""Pytest wrapper launching the APB3 cocotb smoke test for variable depth."""
+
+from pathlib import Path
+
+import pytest
+
+from peakrdl_busdecoder.cpuif.apb3.apb3_cpuif_flat import APB3CpuifFlat
+
+try:  # pragma: no cover - optional dependency shim
+    from cocotb.runner import get_runner
+except ImportError:  # pragma: no cover
+    from cocotb_tools.runner import get_runner
+
+from tests.cocotb_lib.utils import compile_rdl_and_export, get_verilog_sources
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_apb3_variable_depth_1(tmp_path: Path) -> None:
+    """Test APB3 design with max_decode_depth=1."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=APB3CpuifFlat,
+        max_decode_depth=1,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb3_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.apb3.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth1.log"),
+        testcase="test_depth_1",
+    )
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_apb3_variable_depth_2(tmp_path: Path) -> None:
+    """Test APB3 design with max_decode_depth=2."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=APB3CpuifFlat,
+        max_decode_depth=2,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb3_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.apb3.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth2.log"),
+        testcase="test_depth_2",
+    )
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_apb3_variable_depth_0(tmp_path: Path) -> None:
+    """Test APB3 design with max_decode_depth=0 (all levels)."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=APB3CpuifFlat,
+        max_decode_depth=0,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb3_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.apb3.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth0.log"),
+        testcase="test_depth_0",
+    )

tests/cocotb/apb4/smoke/test_register_access.py

@@ -0,0 +1,332 @@
+"""APB4 smoke tests generated from SystemRDL sources."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import cocotb
+from cocotb.triggers import RisingEdge, Timer
+
+from tests.cocotb_lib.handle_utils import SignalHandle
+from tests.cocotb_lib.protocol_utils import (
+    all_index_pairs,
+    find_invalid_address,
+    get_int,
+    load_config,
+    set_value,
+    start_clock,
+)
+
+
+class _Apb4SlaveShim:
+    """Lightweight accessor for the APB4 slave side of the DUT."""
+
+    def __init__(self, dut):
+        prefix = "s_apb"
+        self.PCLK = getattr(dut, f"{prefix}_PCLK", None)
+        self.PRESETn = getattr(dut, f"{prefix}_PRESETn", None)
+        self.PSEL = getattr(dut, f"{prefix}_PSEL")
+        self.PENABLE = getattr(dut, f"{prefix}_PENABLE")
+        self.PWRITE = getattr(dut, f"{prefix}_PWRITE")
+        self.PADDR = getattr(dut, f"{prefix}_PADDR")
+        self.PPROT = getattr(dut, f"{prefix}_PPROT")
+        self.PWDATA = getattr(dut, f"{prefix}_PWDATA")
+        self.PSTRB = getattr(dut, f"{prefix}_PSTRB")
+        self.PRDATA = getattr(dut, f"{prefix}_PRDATA")
+        self.PREADY = getattr(dut, f"{prefix}_PREADY")
+        self.PSLVERR = getattr(dut, f"{prefix}_PSLVERR")
+
+
+def _build_master_table(dut, masters_cfg: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
+    table: dict[str, dict[str, Any]] = {}
+    for master in masters_cfg:
+        port_prefix = master["port_prefix"]
+        entry = {
+            "port_prefix": port_prefix,
+            "indices": [tuple(idx) for idx in master["indices"]] or [tuple()],
+            "outputs": {
+                "PSEL": SignalHandle(dut, f"{port_prefix}_PSEL"),
+                "PENABLE": SignalHandle(dut, f"{port_prefix}_PENABLE"),
+                "PWRITE": SignalHandle(dut, f"{port_prefix}_PWRITE"),
+                "PADDR": SignalHandle(dut, f"{port_prefix}_PADDR"),
+                "PPROT": SignalHandle(dut, f"{port_prefix}_PPROT"),
+                "PWDATA": SignalHandle(dut, f"{port_prefix}_PWDATA"),
+                "PSTRB": SignalHandle(dut, f"{port_prefix}_PSTRB"),
+            },
+            "inputs": {
+                "PRDATA": SignalHandle(dut, f"{port_prefix}_PRDATA"),
+                "PREADY": SignalHandle(dut, f"{port_prefix}_PREADY"),
+                "PSLVERR": SignalHandle(dut, f"{port_prefix}_PSLVERR"),
+            },
+            "inst_size": master["inst_size"],
+            "inst_address": master["inst_address"],
+        }
+        table[master["inst_name"]] = entry
+    return table
+
+
+def _write_pattern(address: int, width: int) -> int:
+    mask = (1 << width) - 1
+    return ((address * 0x1021) ^ 0x1357_9BDF) & mask
+
+
+def _read_pattern(address: int, width: int) -> int:
+    mask = (1 << width) - 1
+    return ((address ^ 0xDEAD_BEE5) + width) & mask
+
+
+@cocotb.test()
+async def test_apb4_address_decoding(dut) -> None:
+    """Drive the APB4 slave interface and verify master fanout across all sampled registers."""
+    config = load_config()
+    slave = _Apb4SlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    await start_clock(slave.PCLK)
+    if slave.PRESETn is not None:
+        slave.PRESETn.value = 1
+
+    slave.PSEL.value = 0
+    slave.PENABLE.value = 0
+    slave.PWRITE.value = 0
+    slave.PADDR.value = 0
+    slave.PPROT.value = 0
+    slave.PWDATA.value = 0
+    slave.PSTRB.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["PRDATA"], idx, 0)
+        set_value(entry["inputs"]["PREADY"], idx, 0)
+        set_value(entry["inputs"]["PSLVERR"], idx, 0)
+
+    if slave.PCLK is not None:
+        await RisingEdge(slave.PCLK)
+    else:
+        await Timer(1, unit="ns")
+
+    addr_mask = (1 << config["address_width"]) - 1
+    strobe_mask = (1 << config["byte_width"]) - 1
+
+    for txn in config["transactions"]:
+        master_name = txn["master"]
+        index = tuple(txn["index"])
+        entry = masters[master_name]
+
+        address = txn["address"] & addr_mask
+        write_data = _write_pattern(address, config["data_width"])
+
+        # Prime master-side inputs for the write phase
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        set_value(entry["inputs"]["PSLVERR"], index, 0)
+
+        # ------------------------------------------------------------------
+        # Setup phase
+        # ------------------------------------------------------------------
+        slave.PADDR.value = address
+        slave.PWDATA.value = write_data
+        slave.PSTRB.value = strobe_mask
+        slave.PPROT.value = 0
+        slave.PWRITE.value = 1
+        slave.PSEL.value = 1
+        slave.PENABLE.value = 0
+
+        dut._log.info(
+            f"Starting transaction {txn['label']} to {master_name}{index} at address 0x{address:08X}"
+        )
+        master_address = (address - entry["inst_address"]) % entry["inst_size"]
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} should assert PSEL for write"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 0, (
+            f"{master_name} must hold PENABLE low in setup"
+        )
+        assert get_int(entry["outputs"]["PWRITE"], index) == 1, f"{master_name} should see write intent"
+        assert get_int(entry["outputs"]["PADDR"], index) == master_address, (
+            f"{master_name} must receive write address"
+        )
+        assert get_int(entry["outputs"]["PWDATA"], index) == write_data, (
+            f"{master_name} must receive write data"
+        )
+        assert get_int(entry["outputs"]["PSTRB"], index) == strobe_mask, (
+            f"{master_name} must receive full strobes"
+        )
+
+        for other_name, other_idx in all_index_pairs(masters):
+            if other_name == master_name and other_idx == index:
+                continue
+            other_entry = masters[other_name]
+            assert get_int(other_entry["outputs"]["PSEL"], other_idx) == 0, (
+                f"{other_name}{other_idx} should remain idle during {txn['label']}"
+            )
+
+        # ------------------------------------------------------------------
+        # Access phase
+        # ------------------------------------------------------------------
+        set_value(entry["inputs"]["PREADY"], index, 1)
+        slave.PENABLE.value = 1
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} must keep PSEL asserted"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 1, (
+            f"{master_name} must assert PENABLE in access"
+        )
+        assert get_int(entry["outputs"]["PADDR"], index) == master_address, (
+            f"{master_name} must keep write address stable"
+        )
+        assert get_int(entry["outputs"]["PWDATA"], index) == write_data, (
+            f"{master_name} must keep write data stable"
+        )
+        assert get_int(entry["outputs"]["PSTRB"], index) == strobe_mask, (
+            f"{master_name} must keep write strobes stable"
+        )
+
+        assert int(slave.PREADY.value) == 1, "Slave ready should reflect selected master"
+        assert int(slave.PSLVERR.value) == 0, "No error expected during write"
+
+        # Return to idle for next transaction
+        slave.PSEL.value = 0
+        slave.PENABLE.value = 0
+        slave.PWRITE.value = 0
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        # ------------------------------------------------------------------
+        # Read phase
+        # ------------------------------------------------------------------
+        read_data = _read_pattern(address, config["data_width"])
+        set_value(entry["inputs"]["PRDATA"], index, read_data)
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        set_value(entry["inputs"]["PSLVERR"], index, 0)
+
+        # ------------------------------------------------------------------
+        # Setup phase
+        # ------------------------------------------------------------------
+        slave.PADDR.value = address
+        slave.PWRITE.value = 0
+        slave.PSEL.value = 1
+        slave.PENABLE.value = 0
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} must assert PSEL for read"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 0, (
+            f"{master_name} must hold PENABLE low in setup"
+        )
+        assert get_int(entry["outputs"]["PWRITE"], index) == 0, (
+            f"{master_name} should deassert write for reads"
+        )
+        assert get_int(entry["outputs"]["PADDR"], index) == master_address, (
+            f"{master_name} must receive read address"
+        )
+
+        for other_name, other_idx in all_index_pairs(masters):
+            if other_name == master_name and other_idx == index:
+                continue
+            other_entry = masters[other_name]
+            assert get_int(other_entry["outputs"]["PSEL"], other_idx) == 0, (
+                f"{other_name}{other_idx} must stay idle during read of {txn['label']}"
+            )
+
+        # ------------------------------------------------------------------
+        # Access phase
+        # ------------------------------------------------------------------
+        set_value(entry["inputs"]["PREADY"], index, 1)
+        slave.PENABLE.value = 1
+
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["PSEL"], index) == 1, f"{master_name} must keep PSEL asserted"
+        assert get_int(entry["outputs"]["PENABLE"], index) == 1, (
+            f"{master_name} must assert PENABLE in access"
+        )
+
+        assert int(slave.PRDATA.value) == read_data, "Slave should observe readback data from master"
+        assert int(slave.PREADY.value) == 1, "Slave ready should follow responding master"
+        assert int(slave.PSLVERR.value) == 0, "Read should complete without error"
+
+        # Reset to idle before progressing
+        slave.PSEL.value = 0
+        slave.PENABLE.value = 0
+        set_value(entry["inputs"]["PREADY"], index, 0)
+        set_value(entry["inputs"]["PRDATA"], index, 0)
+        if slave.PCLK is not None:
+            await RisingEdge(slave.PCLK)
+        else:
+            await Timer(1, unit="ns")
+
+
+@cocotb.test()
+async def test_apb4_invalid_address_response(dut) -> None:
+    """Ensure invalid addresses yield an error response and no master select."""
+    config = load_config()
+    slave = _Apb4SlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    await start_clock(slave.PCLK)
+    if slave.PRESETn is not None:
+        slave.PRESETn.value = 1
+
+    slave.PSEL.value = 0
+    slave.PENABLE.value = 0
+    slave.PWRITE.value = 0
+    slave.PADDR.value = 0
+    slave.PPROT.value = 0
+    slave.PWDATA.value = 0
+    slave.PSTRB.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["PREADY"], idx, 0)
+        set_value(entry["inputs"]["PSLVERR"], idx, 0)
+        set_value(entry["inputs"]["PRDATA"], idx, 0)
+
+    invalid_addr = find_invalid_address(config)
+    if invalid_addr is None:
+        dut._log.warning("No unmapped address found; skipping invalid address test")
+        return
+
+    slave.PADDR.value = invalid_addr
+    slave.PWRITE.value = 1
+    slave.PWDATA.value = _write_pattern(invalid_addr, config["data_width"])
+    slave.PSTRB.value = (1 << config["byte_width"]) - 1
+    slave.PSEL.value = 1
+    slave.PENABLE.value = 0
+
+    if slave.PCLK is not None:
+        await RisingEdge(slave.PCLK)
+    else:
+        await Timer(1, unit="ns")
+
+    slave.PENABLE.value = 1
+
+    if slave.PCLK is not None:
+        await RisingEdge(slave.PCLK)
+    else:
+        await Timer(1, unit="ns")
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        assert get_int(entry["outputs"]["PSEL"], idx) == 0, (
+            f"{master_name}{idx} must stay idle for invalid address"
+        )
+
+    assert int(slave.PREADY.value) == 1, "Invalid address should still complete the transfer"
+    assert int(slave.PSLVERR.value) == 1, "Invalid address should raise PSLVERR"

tests/cocotb/apb4/smoke/test_runner.py

@@ -0,0 +1,89 @@
+"""Pytest wrapper launching the APB4 cocotb smoke tests."""
+
+from __future__ import annotations
+
+import json
+import logging
+from pathlib import Path
+
+import pytest
+
+from peakrdl_busdecoder.cpuif.apb4.apb4_cpuif_flat import APB4CpuifFlat
+
+try:  # pragma: no cover - optional dependency shim
+    from cocotb.runner import get_runner
+except ImportError:  # pragma: no cover
+    from cocotb_tools.runner import get_runner
+
+from tests.cocotb_lib import RDL_CASES
+from tests.cocotb_lib.utils import colorize_cocotb_log, get_verilog_sources, prepare_cpuif_case
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+@pytest.mark.parametrize(("rdl_file", "top_name"), RDL_CASES, ids=[case[1] for case in RDL_CASES])
+def test_apb4_smoke(tmp_path: Path, rdl_file: str, top_name: str) -> None:
+    """Compile each APB4 design variant and execute the cocotb smoke test."""
+    repo_root = Path(__file__).resolve().parents[4]
+    rdl_path = repo_root / "tests" / "cocotb_lib" / "rdl" / rdl_file
+    build_root = tmp_path / top_name
+
+    logging.info(f"Running APB4 smoke test for {rdl_path} with top {top_name}")
+    logging.info(f"Build root: {build_root}")
+
+    module_path, package_path, config = prepare_cpuif_case(
+        str(rdl_path),
+        top_name,
+        build_root,
+        cpuif_cls=APB4CpuifFlat,
+        control_signal="PSEL",
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb4_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    sim_build = build_root / "sim_build"
+
+    build_log_file = build_root / "build.log"
+    sim_log_file = build_root / "simulation.log"
+
+    try:
+        runner.build(
+            sources=sources,
+            hdl_toplevel=module_path.stem,
+            build_dir=sim_build,
+            log_file=str(build_log_file),
+        )
+    except SystemExit as e:
+        # Print build log on failure for easier debugging
+        if build_log_file.exists():
+            logging.error(f"""
+=== Build Log ===
+{colorize_cocotb_log(build_log_file.read_text())}
+=== End Build Log ===
+""")
+        if e.code != 0:
+            raise
+
+    try:
+        runner.test(
+            hdl_toplevel=module_path.stem,
+            test_module="tests.cocotb.apb4.smoke.test_register_access",
+            build_dir=sim_build,
+            log_file=str(sim_log_file),
+            extra_env={"RDL_TEST_CONFIG": json.dumps(config)},
+        )
+    except SystemExit as e:
+        # Print simulation log on failure for easier debugging
+        if sim_log_file.exists():
+            logging.error(f"""
+=== Simulation Log ===
+{colorize_cocotb_log(sim_log_file.read_text())}
+=== End Simulation Log ===
+""")
+        if e.code != 0:
+            raise e

tests/cocotb/apb4/smoke/test_variable_depth.py

@@ -0,0 +1,193 @@
+"""APB4 smoke tests for variable depth design testing max_decode_depth parameter."""
+
+import cocotb
+from cocotb.triggers import Timer
+
+from tests.cocotb_lib.protocol_utils import apb_access, apb_setup
+
+
+class _Apb4SlaveShim:
+    def __init__(self, dut):
+        prefix = "s_apb"
+        self.PSEL = getattr(dut, f"{prefix}_PSEL")
+        self.PENABLE = getattr(dut, f"{prefix}_PENABLE")
+        self.PWRITE = getattr(dut, f"{prefix}_PWRITE")
+        self.PADDR = getattr(dut, f"{prefix}_PADDR")
+        self.PPROT = getattr(dut, f"{prefix}_PPROT")
+        self.PWDATA = getattr(dut, f"{prefix}_PWDATA")
+        self.PSTRB = getattr(dut, f"{prefix}_PSTRB")
+        self.PRDATA = getattr(dut, f"{prefix}_PRDATA")
+        self.PREADY = getattr(dut, f"{prefix}_PREADY")
+        self.PSLVERR = getattr(dut, f"{prefix}_PSLVERR")
+
+
+class _Apb4MasterShim:
+    def __init__(self, dut, base: str):
+        self.PSEL = getattr(dut, f"{base}_PSEL")
+        self.PENABLE = getattr(dut, f"{base}_PENABLE")
+        self.PWRITE = getattr(dut, f"{base}_PWRITE")
+        self.PADDR = getattr(dut, f"{base}_PADDR")
+        self.PPROT = getattr(dut, f"{base}_PPROT")
+        self.PWDATA = getattr(dut, f"{base}_PWDATA")
+        self.PSTRB = getattr(dut, f"{base}_PSTRB")
+        self.PRDATA = getattr(dut, f"{base}_PRDATA")
+        self.PREADY = getattr(dut, f"{base}_PREADY")
+        self.PSLVERR = getattr(dut, f"{base}_PSLVERR")
+
+
+def _apb4_slave(dut):
+    return getattr(dut, "s_apb", None) or _Apb4SlaveShim(dut)
+
+
+def _apb4_master(dut, base: str):
+    return getattr(dut, base, None) or _Apb4MasterShim(dut, base)
+
+
+@cocotb.test()
+async def test_depth_1(dut):
+    """Test max_decode_depth=1 - should have interface for inner1 only."""
+    s_apb = _apb4_slave(dut)
+
+    # At depth 1, we should have m_apb_inner1 but not deeper interfaces
+    inner1 = _apb4_master(dut, "m_apb_inner1")
+
+    # Default slave side inputs
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    s_apb.PWRITE.value = 0
+    s_apb.PADDR.value = 0
+    s_apb.PWDATA.value = 0
+    s_apb.PPROT.value = 0
+    s_apb.PSTRB.value = 0
+
+    inner1.PRDATA.value = 0
+    inner1.PREADY.value = 0
+    inner1.PSLVERR.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select inner1)
+    inner1.PREADY.value = 1
+    await apb_setup(s_apb, 0x0, True, 0x12345678)
+    await apb_access(s_apb)
+
+    assert int(inner1.PSEL.value) == 1, "inner1 must be selected"
+    assert int(inner1.PWRITE.value) == 1, "Write should propagate"
+    assert int(s_apb.PREADY.value) == 1, "Ready should mirror master"
+
+
+@cocotb.test()
+async def test_depth_2(dut):
+    """Test max_decode_depth=2 - should have interfaces for reg1 and inner2."""
+    s_apb = _apb4_slave(dut)
+
+    # At depth 2, we should have m_apb_reg1 and m_apb_inner2
+    reg1 = _apb4_master(dut, "m_apb_reg1")
+    inner2 = _apb4_master(dut, "m_apb_inner2")
+
+    # Default slave side inputs
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    s_apb.PWRITE.value = 0
+    s_apb.PADDR.value = 0
+    s_apb.PWDATA.value = 0
+    s_apb.PPROT.value = 0
+    s_apb.PSTRB.value = 0
+
+    reg1.PRDATA.value = 0
+    reg1.PREADY.value = 0
+    reg1.PSLVERR.value = 0
+
+    inner2.PRDATA.value = 0
+    inner2.PREADY.value = 0
+    inner2.PSLVERR.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select reg1)
+    reg1.PREADY.value = 1
+    await apb_setup(s_apb, 0x0, True, 0xABCDEF01)
+    await apb_access(s_apb)
+
+    assert int(reg1.PSEL.value) == 1, "reg1 must be selected for address 0x0"
+    assert int(inner2.PSEL.value) == 0, "inner2 should not be selected"
+
+    # Reset
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    reg1.PREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x10 (should select inner2)
+    inner2.PREADY.value = 1
+    await apb_setup(s_apb, 0x10, True, 0x23456789)
+    await apb_access(s_apb)
+
+    assert int(inner2.PSEL.value) == 1, "inner2 must be selected for address 0x10"
+    assert int(reg1.PSEL.value) == 0, "reg1 should not be selected"
+
+
+@cocotb.test()
+async def test_depth_0(dut):
+    """Test max_decode_depth=0 - should have interfaces for all leaf registers."""
+    s_apb = _apb4_slave(dut)
+
+    # At depth 0, we should have all leaf registers: reg1, reg2, reg2b
+    reg1 = _apb4_master(dut, "m_apb_reg1")
+    reg2 = _apb4_master(dut, "m_apb_reg2")
+    reg2b = _apb4_master(dut, "m_apb_reg2b")
+
+    # Default slave side inputs
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    s_apb.PWRITE.value = 0
+    s_apb.PADDR.value = 0
+    s_apb.PWDATA.value = 0
+    s_apb.PPROT.value = 0
+    s_apb.PSTRB.value = 0
+
+    for master in [reg1, reg2, reg2b]:
+        master.PRDATA.value = 0
+        master.PREADY.value = 0
+        master.PSLVERR.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select reg1)
+    reg1.PREADY.value = 1
+    await apb_setup(s_apb, 0x0, True, 0x11111111)
+    await apb_access(s_apb)
+
+    assert int(reg1.PSEL.value) == 1, "reg1 must be selected for address 0x0"
+    assert int(reg2.PSEL.value) == 0, "reg2 should not be selected"
+    assert int(reg2b.PSEL.value) == 0, "reg2b should not be selected"
+
+    # Reset
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    reg1.PREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x10 (should select reg2)
+    reg2.PREADY.value = 1
+    await apb_setup(s_apb, 0x10, True, 0x22222222)
+    await apb_access(s_apb)
+
+    assert int(reg2.PSEL.value) == 1, "reg2 must be selected for address 0x10"
+    assert int(reg1.PSEL.value) == 0, "reg1 should not be selected"
+    assert int(reg2b.PSEL.value) == 0, "reg2b should not be selected"
+
+    # Reset
+    s_apb.PSEL.value = 0
+    s_apb.PENABLE.value = 0
+    reg2.PREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x14 (should select reg2b)
+    reg2b.PREADY.value = 1
+    await apb_setup(s_apb, 0x14, True, 0x33333333)
+    await apb_access(s_apb)
+
+    assert int(reg2b.PSEL.value) == 1, "reg2b must be selected for address 0x14"
+    assert int(reg1.PSEL.value) == 0, "reg1 should not be selected"
+    assert int(reg2.PSEL.value) == 0, "reg2 should not be selected"

tests/cocotb/apb4/smoke/test_variable_depth_runner.py

@@ -0,0 +1,131 @@
+"""Pytest wrapper launching the APB4 cocotb smoke test for variable depth."""
+
+from pathlib import Path
+
+import pytest
+
+from peakrdl_busdecoder.cpuif.apb4.apb4_cpuif_flat import APB4CpuifFlat
+
+try:  # pragma: no cover - optional dependency shim
+    from cocotb.runner import get_runner
+except ImportError:  # pragma: no cover
+    from cocotb_tools.runner import get_runner
+
+from tests.cocotb_lib.utils import compile_rdl_and_export, get_verilog_sources
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_apb4_variable_depth_1(tmp_path: Path) -> None:
+    """Test APB4 design with max_decode_depth=1."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=APB4CpuifFlat,
+        max_decode_depth=1,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb4_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+        log_file=str(tmp_path / "build_depth_1.log"),
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.apb4.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth1.log"),
+        testcase="test_depth_1",
+    )
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_apb4_variable_depth_2(tmp_path: Path) -> None:
+    """Test APB4 design with max_decode_depth=2."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=APB4CpuifFlat,
+        max_decode_depth=2,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb4_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+        log_file=str(tmp_path / "build_depth_2.log"),
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.apb4.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth_2.log"),
+        testcase="test_depth_2",
+    )
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_apb4_variable_depth_0(tmp_path: Path) -> None:
+    """Test APB4 design with max_decode_depth=0 (all levels)."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=APB4CpuifFlat,
+        max_decode_depth=0,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "apb4_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+        log_file=str(tmp_path / "build_depth_0.log"),
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.apb4.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth_0.log"),
+        testcase="test_depth_0",
+    )

tests/cocotb/axi4lite/smoke/test_register_access.py

@@ -0,0 +1,357 @@
+"""AXI4-Lite smoke test driven from SystemRDL-generated register maps."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import cocotb
+from cocotb.triggers import Timer
+
+from tests.cocotb_lib.handle_utils import SignalHandle
+from tests.cocotb_lib.protocol_utils import (
+    all_index_pairs,
+    find_invalid_address,
+    get_int,
+    load_config,
+    set_value,
+)
+
+
+class _AxilSlaveShim:
+    """Accessor for AXI4-Lite slave ports on the DUT."""
+
+    def __init__(self, dut):
+        prefix = "s_axil"
+        self.AWREADY = getattr(dut, f"{prefix}_AWREADY")
+        self.AWVALID = getattr(dut, f"{prefix}_AWVALID")
+        self.AWADDR = getattr(dut, f"{prefix}_AWADDR")
+        self.AWPROT = getattr(dut, f"{prefix}_AWPROT")
+        self.WREADY = getattr(dut, f"{prefix}_WREADY")
+        self.WVALID = getattr(dut, f"{prefix}_WVALID")
+        self.WDATA = getattr(dut, f"{prefix}_WDATA")
+        self.WSTRB = getattr(dut, f"{prefix}_WSTRB")
+        self.BREADY = getattr(dut, f"{prefix}_BREADY")
+        self.BVALID = getattr(dut, f"{prefix}_BVALID")
+        self.BRESP = getattr(dut, f"{prefix}_BRESP")
+        self.ARREADY = getattr(dut, f"{prefix}_ARREADY")
+        self.ARVALID = getattr(dut, f"{prefix}_ARVALID")
+        self.ARADDR = getattr(dut, f"{prefix}_ARADDR")
+        self.ARPROT = getattr(dut, f"{prefix}_ARPROT")
+        self.RREADY = getattr(dut, f"{prefix}_RREADY")
+        self.RVALID = getattr(dut, f"{prefix}_RVALID")
+        self.RDATA = getattr(dut, f"{prefix}_RDATA")
+        self.RRESP = getattr(dut, f"{prefix}_RRESP")
+
+
+def _build_master_table(dut, masters_cfg: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
+    table: dict[str, dict[str, Any]] = {}
+    for master in masters_cfg:
+        prefix = master["port_prefix"]
+        entry = {
+            "indices": [tuple(idx) for idx in master["indices"]] or [tuple()],
+            "outputs": {
+                "AWVALID": SignalHandle(dut, f"{prefix}_AWVALID"),
+                "AWADDR": SignalHandle(dut, f"{prefix}_AWADDR"),
+                "AWPROT": SignalHandle(dut, f"{prefix}_AWPROT"),
+                "WVALID": SignalHandle(dut, f"{prefix}_WVALID"),
+                "WDATA": SignalHandle(dut, f"{prefix}_WDATA"),
+                "WSTRB": SignalHandle(dut, f"{prefix}_WSTRB"),
+                "ARVALID": SignalHandle(dut, f"{prefix}_ARVALID"),
+                "ARADDR": SignalHandle(dut, f"{prefix}_ARADDR"),
+                "ARPROT": SignalHandle(dut, f"{prefix}_ARPROT"),
+            },
+            "inputs": {
+                "AWREADY": SignalHandle(dut, f"{prefix}_AWREADY"),
+                "WREADY": SignalHandle(dut, f"{prefix}_WREADY"),
+                "BVALID": SignalHandle(dut, f"{prefix}_BVALID"),
+                "BRESP": SignalHandle(dut, f"{prefix}_BRESP"),
+                "ARREADY": SignalHandle(dut, f"{prefix}_ARREADY"),
+                "RVALID": SignalHandle(dut, f"{prefix}_RVALID"),
+                "RDATA": SignalHandle(dut, f"{prefix}_RDATA"),
+                "RRESP": SignalHandle(dut, f"{prefix}_RRESP"),
+            },
+            "inst_size": master["inst_size"],
+            "inst_address": master["inst_address"],
+        }
+        table[master["inst_name"]] = entry
+    return table
+
+
+def _write_pattern(address: int, width: int) -> int:
+    mask = (1 << width) - 1
+    return ((address * 0x3105) ^ 0x1357_9BDF) & mask
+
+
+def _read_pattern(address: int, width: int) -> int:
+    mask = (1 << width) - 1
+    return ((address ^ 0x2468_ACED) + width) & mask
+
+
+@cocotb.test()
+async def test_axi4lite_address_decoding(dut) -> None:
+    """Stimulate AXI4-Lite slave channels and verify master port selection."""
+    config = load_config()
+    slave = _AxilSlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    slave.AWVALID.value = 0
+    slave.AWADDR.value = 0
+    slave.AWPROT.value = 0
+    slave.WVALID.value = 0
+    slave.WDATA.value = 0
+    slave.WSTRB.value = 0
+    slave.BREADY.value = 0
+    slave.ARVALID.value = 0
+    slave.ARADDR.value = 0
+    slave.ARPROT.value = 0
+    slave.RREADY.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["AWREADY"], idx, 0)
+        set_value(entry["inputs"]["WREADY"], idx, 0)
+        set_value(entry["inputs"]["BVALID"], idx, 0)
+        set_value(entry["inputs"]["BRESP"], idx, 0)
+        set_value(entry["inputs"]["ARREADY"], idx, 0)
+        set_value(entry["inputs"]["RVALID"], idx, 0)
+        set_value(entry["inputs"]["RDATA"], idx, 0)
+        set_value(entry["inputs"]["RRESP"], idx, 0)
+
+    await Timer(1, unit="ns")
+
+    addr_mask = (1 << config["address_width"]) - 1
+    strobe_mask = (1 << config["byte_width"]) - 1
+
+    for txn in config["transactions"]:
+        master_name = txn["master"]
+        index = tuple(txn["index"])
+        entry = masters[master_name]
+
+        address = txn["address"] & addr_mask
+        write_data = _write_pattern(address, config["data_width"])
+
+        set_value(entry["inputs"]["BVALID"], index, 1)
+        set_value(entry["inputs"]["BRESP"], index, 0)
+
+        slave.AWADDR.value = address
+        slave.AWPROT.value = 0
+        slave.AWVALID.value = 1
+        slave.WDATA.value = write_data
+        slave.WSTRB.value = strobe_mask
+        slave.WVALID.value = 1
+        slave.BREADY.value = 1
+
+        dut._log.info(
+            f"Starting transaction {txn['label']} to {master_name}{index} at address 0x{address:08X}"
+        )
+        master_address = (address - entry["inst_address"]) % entry["inst_size"]
+
+        await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["AWVALID"], index) == 1, f"{master_name} should see AWVALID asserted"
+        assert get_int(entry["outputs"]["AWADDR"], index) == master_address, (
+            f"{master_name} must receive AWADDR"
+        )
+        assert get_int(entry["outputs"]["WVALID"], index) == 1, f"{master_name} should see WVALID asserted"
+        assert get_int(entry["outputs"]["WDATA"], index) == write_data, f"{master_name} must receive WDATA"
+        assert get_int(entry["outputs"]["WSTRB"], index) == strobe_mask, f"{master_name} must receive WSTRB"
+        assert int(slave.AWREADY.value) == 1, "AWREADY should assert when write address/data are valid"
+        assert int(slave.WREADY.value) == 1, "WREADY should assert when write address/data are valid"
+
+        for other_name, other_idx in all_index_pairs(masters):
+            if other_name == master_name and other_idx == index:
+                continue
+            other_entry = masters[other_name]
+            assert get_int(other_entry["outputs"]["AWVALID"], other_idx) == 0, (
+                f"{other_name}{other_idx} AWVALID should remain low during {txn['label']}"
+            )
+            assert get_int(other_entry["outputs"]["WVALID"], other_idx) == 0, (
+                f"{other_name}{other_idx} WVALID should remain low during {txn['label']}"
+            )
+
+        assert int(slave.BVALID.value) == 1, "Slave should observe BVALID from selected master"
+        assert int(slave.BRESP.value) == 0, "BRESP should indicate OKAY on write"
+
+        slave.AWVALID.value = 0
+        slave.WVALID.value = 0
+        slave.BREADY.value = 0
+        set_value(entry["inputs"]["BVALID"], index, 0)
+        await Timer(1, unit="ns")
+
+        read_data = _read_pattern(address, config["data_width"])
+        set_value(entry["inputs"]["RVALID"], index, 1)
+        set_value(entry["inputs"]["RDATA"], index, read_data)
+        set_value(entry["inputs"]["RRESP"], index, 0)
+
+        slave.ARADDR.value = address
+        slave.ARPROT.value = 0
+        slave.ARVALID.value = 1
+        slave.RREADY.value = 1
+
+        await Timer(1, unit="ns")
+
+        assert get_int(entry["outputs"]["ARVALID"], index) == 1, f"{master_name} should assert ARVALID"
+        assert get_int(entry["outputs"]["ARADDR"], index) == master_address, (
+            f"{master_name} must receive ARADDR"
+        )
+        assert int(slave.ARREADY.value) == 1, "ARREADY should assert when ARVALID is high"
+
+        for other_name, other_idx in all_index_pairs(masters):
+            if other_name == master_name and other_idx == index:
+                continue
+            other_entry = masters[other_name]
+            assert get_int(other_entry["outputs"]["ARVALID"], other_idx) == 0, (
+                f"{other_name}{other_idx} ARVALID should remain low during read of {txn['label']}"
+            )
+
+        assert int(slave.RVALID.value) == 1, "Slave should observe RVALID when master responds"
+        assert int(slave.RDATA.value) == read_data, "Read data must fold back to slave"
+        assert int(slave.RRESP.value) == 0, "Read response should indicate success"
+
+        slave.ARVALID.value = 0
+        slave.RREADY.value = 0
+        set_value(entry["inputs"]["RVALID"], index, 0)
+        set_value(entry["inputs"]["RDATA"], index, 0)
+        await Timer(1, unit="ns")
+
+
+@cocotb.test()
+async def test_axi4lite_invalid_write_handshake(dut) -> None:
+    """Ensure mismatched AW/W valid signals raise an error and are ignored."""
+    config = load_config()
+    slave = _AxilSlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    slave.AWVALID.value = 0
+    slave.AWADDR.value = 0
+    slave.AWPROT.value = 0
+    slave.WVALID.value = 0
+    slave.WDATA.value = 0
+    slave.WSTRB.value = 0
+    slave.BREADY.value = 0
+    slave.ARVALID.value = 0
+    slave.ARADDR.value = 0
+    slave.ARPROT.value = 0
+    slave.RREADY.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["AWREADY"], idx, 0)
+        set_value(entry["inputs"]["WREADY"], idx, 0)
+        set_value(entry["inputs"]["BVALID"], idx, 0)
+        set_value(entry["inputs"]["BRESP"], idx, 0)
+        set_value(entry["inputs"]["ARREADY"], idx, 0)
+        set_value(entry["inputs"]["RVALID"], idx, 0)
+        set_value(entry["inputs"]["RDATA"], idx, 0)
+        set_value(entry["inputs"]["RRESP"], idx, 0)
+
+    await Timer(1, unit="ns")
+
+    if not config["transactions"]:
+        dut._log.warning("No transactions available; skipping invalid handshake test")
+        return
+
+    bad_addr = config["transactions"][0]["address"] & ((1 << config["address_width"]) - 1)
+    slave.AWADDR.value = bad_addr
+    slave.AWPROT.value = 0
+    slave.AWVALID.value = 1
+    slave.WVALID.value = 0
+    slave.BREADY.value = 1
+
+    await Timer(1, unit="ns")
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        assert get_int(entry["outputs"]["AWVALID"], idx) == 0, (
+            f"{master_name}{idx} must not see AWVALID on invalid handshake"
+        )
+        assert get_int(entry["outputs"]["WVALID"], idx) == 0, (
+            f"{master_name}{idx} must not see WVALID on invalid handshake"
+        )
+
+    assert int(slave.AWREADY.value) == 0, "AWREADY must remain low on invalid write handshake"
+    assert int(slave.WREADY.value) == 0, "WREADY must remain low on invalid write handshake"
+    assert int(slave.BVALID.value) == 1, "Invalid write handshake should return BVALID"
+    assert int(slave.BRESP.value) == 2, "Invalid write handshake should return SLVERR"
+
+
+@cocotb.test()
+async def test_axi4lite_invalid_address_response(dut) -> None:
+    """Ensure unmapped addresses return error responses and do not select a master."""
+    config = load_config()
+    slave = _AxilSlaveShim(dut)
+    masters = _build_master_table(dut, config["masters"])
+
+    slave.AWVALID.value = 0
+    slave.AWADDR.value = 0
+    slave.AWPROT.value = 0
+    slave.WVALID.value = 0
+    slave.WDATA.value = 0
+    slave.WSTRB.value = 0
+    slave.BREADY.value = 0
+    slave.ARVALID.value = 0
+    slave.ARADDR.value = 0
+    slave.ARPROT.value = 0
+    slave.RREADY.value = 0
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        set_value(entry["inputs"]["AWREADY"], idx, 0)
+        set_value(entry["inputs"]["WREADY"], idx, 0)
+        set_value(entry["inputs"]["BVALID"], idx, 0)
+        set_value(entry["inputs"]["BRESP"], idx, 0)
+        set_value(entry["inputs"]["ARREADY"], idx, 0)
+        set_value(entry["inputs"]["RVALID"], idx, 0)
+        set_value(entry["inputs"]["RDATA"], idx, 0)
+        set_value(entry["inputs"]["RRESP"], idx, 0)
+
+    await Timer(1, unit="ns")
+
+    invalid_addr = find_invalid_address(config)
+    if invalid_addr is None:
+        dut._log.warning("No unmapped address found; skipping invalid address test")
+        return
+
+    # Invalid read
+    slave.ARADDR.value = invalid_addr
+    slave.ARPROT.value = 0
+    slave.ARVALID.value = 1
+    slave.RREADY.value = 1
+
+    await Timer(1, unit="ns")
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        assert get_int(entry["outputs"]["ARVALID"], idx) == 0, (
+            f"{master_name}{idx} must stay idle for invalid read address"
+        )
+
+    assert int(slave.RVALID.value) == 1, "Invalid read should return RVALID"
+    assert int(slave.RRESP.value) == 2, "Invalid read should return SLVERR"
+
+    slave.ARVALID.value = 0
+    slave.RREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Invalid write
+    slave.AWADDR.value = invalid_addr
+    slave.AWPROT.value = 0
+    slave.AWVALID.value = 1
+    slave.WDATA.value = 0xA5A5_5A5A
+    slave.WSTRB.value = (1 << config["byte_width"]) - 1
+    slave.WVALID.value = 1
+    slave.BREADY.value = 1
+
+    await Timer(1, unit="ns")
+
+    for master_name, idx in all_index_pairs(masters):
+        entry = masters[master_name]
+        assert get_int(entry["outputs"]["AWVALID"], idx) == 0, (
+            f"{master_name}{idx} must stay idle for invalid write address"
+        )
+        assert get_int(entry["outputs"]["WVALID"], idx) == 0, (
+            f"{master_name}{idx} must stay idle for invalid write address"
+        )
+
+    assert int(slave.BVALID.value) == 1, "Invalid write should return BVALID"
+    assert int(slave.BRESP.value) == 2, "Invalid write should return SLVERR"

tests/cocotb/axi4lite/smoke/test_runner.py

@@ -0,0 +1,86 @@
+"""Pytest wrapper launching the AXI4-Lite cocotb smoke tests."""
+
+from __future__ import annotations
+
+import json
+import logging
+from pathlib import Path
+
+import pytest
+
+from peakrdl_busdecoder.cpuif.axi4lite.axi4_lite_cpuif_flat import AXI4LiteCpuifFlat
+
+try:  # pragma: no cover - optional dependency shim
+    from cocotb.runner import get_runner
+except ImportError:  # pragma: no cover
+    from cocotb_tools.runner import get_runner
+
+from tests.cocotb_lib import RDL_CASES
+from tests.cocotb_lib.utils import colorize_cocotb_log, get_verilog_sources, prepare_cpuif_case
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+@pytest.mark.parametrize(("rdl_file", "top_name"), RDL_CASES, ids=[case[1] for case in RDL_CASES])
+def test_axi4lite_smoke(tmp_path: Path, rdl_file: str, top_name: str) -> None:
+    """Compile each AXI4-Lite design variant and execute the cocotb smoke test."""
+    repo_root = Path(__file__).resolve().parents[4]
+    rdl_path = repo_root / "tests" / "cocotb_lib" / "rdl" / rdl_file
+    build_root = tmp_path / top_name
+
+    module_path, package_path, config = prepare_cpuif_case(
+        str(rdl_path),
+        top_name,
+        build_root,
+        cpuif_cls=AXI4LiteCpuifFlat,
+        control_signal="AWVALID",
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "axi4lite_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    sim_build = build_root / "sim_build"
+
+    build_log_file = build_root / "build.log"
+    sim_log_file = build_root / "simulation.log"
+
+    try:
+        runner.build(
+            sources=sources,
+            hdl_toplevel=module_path.stem,
+            build_dir=sim_build,
+            log_file=str(build_log_file),
+        )
+    except SystemExit as e:
+        # Print build log on failure for easier debugging
+        if build_log_file.exists():
+            logging.error(f"""
+=== Build Log ===
+{colorize_cocotb_log(build_log_file.read_text())}
+=== End Build Log ===
+""")
+        if e.code != 0:
+            raise
+
+    try:
+        runner.test(
+            hdl_toplevel=module_path.stem,
+            test_module="tests.cocotb.axi4lite.smoke.test_register_access",
+            build_dir=sim_build,
+            log_file=str(sim_log_file),
+            extra_env={"RDL_TEST_CONFIG": json.dumps(config)},
+        )
+    except SystemExit as e:
+        # Print simulation log on failure for easier debugging
+        if sim_log_file.exists():
+            logging.error(f"""
+=== Simulation Log ===
+{colorize_cocotb_log(sim_log_file.read_text())}
+=== End Simulation Log ===
+""")
+        if e.code != 0:
+            raise

tests/cocotb/axi4lite/smoke/test_variable_depth.py

@@ -0,0 +1,271 @@
+"""AXI4-Lite smoke tests for variable depth design testing max_decode_depth parameter."""
+
+import cocotb
+from cocotb.triggers import Timer
+
+
+class _AxilSlaveShim:
+    def __init__(self, dut):
+        prefix = "s_axil"
+        self.AWREADY = getattr(dut, f"{prefix}_AWREADY")
+        self.AWVALID = getattr(dut, f"{prefix}_AWVALID")
+        self.AWADDR = getattr(dut, f"{prefix}_AWADDR")
+        self.AWPROT = getattr(dut, f"{prefix}_AWPROT")
+        self.WREADY = getattr(dut, f"{prefix}_WREADY")
+        self.WVALID = getattr(dut, f"{prefix}_WVALID")
+        self.WDATA = getattr(dut, f"{prefix}_WDATA")
+        self.WSTRB = getattr(dut, f"{prefix}_WSTRB")
+        self.BREADY = getattr(dut, f"{prefix}_BREADY")
+        self.BVALID = getattr(dut, f"{prefix}_BVALID")
+        self.BRESP = getattr(dut, f"{prefix}_BRESP")
+        self.ARREADY = getattr(dut, f"{prefix}_ARREADY")
+        self.ARVALID = getattr(dut, f"{prefix}_ARVALID")
+        self.ARADDR = getattr(dut, f"{prefix}_ARADDR")
+        self.ARPROT = getattr(dut, f"{prefix}_ARPROT")
+        self.RREADY = getattr(dut, f"{prefix}_RREADY")
+        self.RVALID = getattr(dut, f"{prefix}_RVALID")
+        self.RDATA = getattr(dut, f"{prefix}_RDATA")
+        self.RRESP = getattr(dut, f"{prefix}_RRESP")
+
+
+class _AxilMasterShim:
+    def __init__(self, dut, base: str):
+        self.AWREADY = getattr(dut, f"{base}_AWREADY")
+        self.AWVALID = getattr(dut, f"{base}_AWVALID")
+        self.AWADDR = getattr(dut, f"{base}_AWADDR")
+        self.AWPROT = getattr(dut, f"{base}_AWPROT")
+        self.WREADY = getattr(dut, f"{base}_WREADY")
+        self.WVALID = getattr(dut, f"{base}_WVALID")
+        self.WDATA = getattr(dut, f"{base}_WDATA")
+        self.WSTRB = getattr(dut, f"{base}_WSTRB")
+        self.BREADY = getattr(dut, f"{base}_BREADY")
+        self.BVALID = getattr(dut, f"{base}_BVALID")
+        self.BRESP = getattr(dut, f"{base}_BRESP")
+        self.ARREADY = getattr(dut, f"{base}_ARREADY")
+        self.ARVALID = getattr(dut, f"{base}_ARVALID")
+        self.ARADDR = getattr(dut, f"{base}_ARADDR")
+        self.ARPROT = getattr(dut, f"{base}_ARPROT")
+        self.RREADY = getattr(dut, f"{base}_RREADY")
+        self.RVALID = getattr(dut, f"{base}_RVALID")
+        self.RDATA = getattr(dut, f"{base}_RDATA")
+        self.RRESP = getattr(dut, f"{base}_RRESP")
+
+
+def _axil_slave(dut):
+    return getattr(dut, "s_axil", None) or _AxilSlaveShim(dut)
+
+
+def _axil_master(dut, base: str):
+    return getattr(dut, base, None) or _AxilMasterShim(dut, base)
+
+
+@cocotb.test()
+async def test_depth_1(dut):
+    """Test max_decode_depth=1 - should have interface for inner1 only."""
+    s_axil = _axil_slave(dut)
+
+    # At depth 1, we should have m_axil_inner1 but not deeper interfaces
+    inner1 = _axil_master(dut, "m_axil_inner1")
+
+    # Default slave side inputs
+    s_axil.AWVALID.value = 0
+    s_axil.AWADDR.value = 0
+    s_axil.AWPROT.value = 0
+    s_axil.WVALID.value = 0
+    s_axil.WDATA.value = 0
+    s_axil.WSTRB.value = 0
+    s_axil.BREADY.value = 0
+    s_axil.ARVALID.value = 0
+    s_axil.ARADDR.value = 0
+    s_axil.ARPROT.value = 0
+    s_axil.RREADY.value = 0
+
+    inner1.AWREADY.value = 0
+    inner1.WREADY.value = 0
+    inner1.BVALID.value = 0
+    inner1.BRESP.value = 0
+    inner1.ARREADY.value = 0
+    inner1.RVALID.value = 0
+    inner1.RDATA.value = 0
+    inner1.RRESP.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select inner1)
+    inner1.AWREADY.value = 1
+    inner1.WREADY.value = 1
+    s_axil.AWVALID.value = 1
+    s_axil.AWADDR.value = 0x0
+    s_axil.WVALID.value = 1
+    s_axil.WDATA.value = 0x12345678
+    s_axil.WSTRB.value = 0xF
+
+    await Timer(1, unit="ns")
+
+    assert int(inner1.AWVALID.value) == 1, "inner1 write address valid must be set"
+    assert int(inner1.WVALID.value) == 1, "inner1 write data valid must be set"
+
+
+@cocotb.test()
+async def test_depth_2(dut):
+    """Test max_decode_depth=2 - should have interfaces for reg1 and inner2."""
+    s_axil = _axil_slave(dut)
+
+    # At depth 2, we should have m_axil_reg1 and m_axil_inner2
+    reg1 = _axil_master(dut, "m_axil_reg1")
+    inner2 = _axil_master(dut, "m_axil_inner2")
+
+    # Default slave side inputs
+    s_axil.AWVALID.value = 0
+    s_axil.AWADDR.value = 0
+    s_axil.AWPROT.value = 0
+    s_axil.WVALID.value = 0
+    s_axil.WDATA.value = 0
+    s_axil.WSTRB.value = 0
+    s_axil.BREADY.value = 0
+    s_axil.ARVALID.value = 0
+    s_axil.ARADDR.value = 0
+    s_axil.ARPROT.value = 0
+    s_axil.RREADY.value = 0
+
+    for master in [reg1, inner2]:
+        master.AWREADY.value = 0
+        master.WREADY.value = 0
+        master.BVALID.value = 0
+        master.BRESP.value = 0
+        master.ARREADY.value = 0
+        master.RVALID.value = 0
+        master.RDATA.value = 0
+        master.RRESP.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select reg1)
+    reg1.AWREADY.value = 1
+    reg1.WREADY.value = 1
+    s_axil.AWVALID.value = 1
+    s_axil.AWADDR.value = 0x0
+    s_axil.WVALID.value = 1
+    s_axil.WDATA.value = 0xABCDEF01
+    s_axil.WSTRB.value = 0xF
+
+    await Timer(1, unit="ns")
+
+    assert int(reg1.AWVALID.value) == 1, "reg1 must be selected for address 0x0"
+    assert int(inner2.AWVALID.value) == 0, "inner2 should not be selected"
+
+    # Reset
+    s_axil.AWVALID.value = 0
+    s_axil.WVALID.value = 0
+    reg1.AWREADY.value = 0
+    reg1.WREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x10 (should select inner2)
+    inner2.AWREADY.value = 1
+    inner2.WREADY.value = 1
+    s_axil.AWVALID.value = 1
+    s_axil.AWADDR.value = 0x10
+    s_axil.WVALID.value = 1
+    s_axil.WDATA.value = 0x23456789
+    s_axil.WSTRB.value = 0xF
+
+    await Timer(1, unit="ns")
+
+    assert int(inner2.AWVALID.value) == 1, "inner2 must be selected for address 0x10"
+    assert int(reg1.AWVALID.value) == 0, "reg1 should not be selected"
+
+
+@cocotb.test()
+async def test_depth_0(dut):
+    """Test max_decode_depth=0 - should have interfaces for all leaf registers."""
+    s_axil = _axil_slave(dut)
+
+    # At depth 0, we should have all leaf registers: reg1, reg2, reg2b
+    reg1 = _axil_master(dut, "m_axil_reg1")
+    reg2 = _axil_master(dut, "m_axil_reg2")
+    reg2b = _axil_master(dut, "m_axil_reg2b")
+
+    # Default slave side inputs
+    s_axil.AWVALID.value = 0
+    s_axil.AWADDR.value = 0
+    s_axil.AWPROT.value = 0
+    s_axil.WVALID.value = 0
+    s_axil.WDATA.value = 0
+    s_axil.WSTRB.value = 0
+    s_axil.BREADY.value = 0
+    s_axil.ARVALID.value = 0
+    s_axil.ARADDR.value = 0
+    s_axil.ARPROT.value = 0
+    s_axil.RREADY.value = 0
+
+    for master in [reg1, reg2, reg2b]:
+        master.AWREADY.value = 0
+        master.WREADY.value = 0
+        master.BVALID.value = 0
+        master.BRESP.value = 0
+        master.ARREADY.value = 0
+        master.RVALID.value = 0
+        master.RDATA.value = 0
+        master.RRESP.value = 0
+
+    await Timer(1, unit="ns")
+
+    # Write to address 0x0 (should select reg1)
+    reg1.AWREADY.value = 1
+    reg1.WREADY.value = 1
+    s_axil.AWVALID.value = 1
+    s_axil.AWADDR.value = 0x0
+    s_axil.WVALID.value = 1
+    s_axil.WDATA.value = 0x11111111
+    s_axil.WSTRB.value = 0xF
+
+    await Timer(1, unit="ns")
+
+    assert int(reg1.AWVALID.value) == 1, "reg1 must be selected for address 0x0"
+    assert int(reg2.AWVALID.value) == 0, "reg2 should not be selected"
+    assert int(reg2b.AWVALID.value) == 0, "reg2b should not be selected"
+
+    # Reset
+    s_axil.AWVALID.value = 0
+    s_axil.WVALID.value = 0
+    reg1.AWREADY.value = 0
+    reg1.WREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x10 (should select reg2)
+    reg2.AWREADY.value = 1
+    reg2.WREADY.value = 1
+    s_axil.AWVALID.value = 1
+    s_axil.AWADDR.value = 0x10
+    s_axil.WVALID.value = 1
+    s_axil.WDATA.value = 0x22222222
+    s_axil.WSTRB.value = 0xF
+
+    await Timer(1, unit="ns")
+
+    assert int(reg2.AWVALID.value) == 1, "reg2 must be selected for address 0x10"
+    assert int(reg1.AWVALID.value) == 0, "reg1 should not be selected"
+    assert int(reg2b.AWVALID.value) == 0, "reg2b should not be selected"
+
+    # Reset
+    s_axil.AWVALID.value = 0
+    s_axil.WVALID.value = 0
+    reg2.AWREADY.value = 0
+    reg2.WREADY.value = 0
+    await Timer(1, unit="ns")
+
+    # Write to address 0x14 (should select reg2b)
+    reg2b.AWREADY.value = 1
+    reg2b.WREADY.value = 1
+    s_axil.AWVALID.value = 1
+    s_axil.AWADDR.value = 0x14
+    s_axil.WVALID.value = 1
+    s_axil.WDATA.value = 0x33333333
+    s_axil.WSTRB.value = 0xF
+
+    await Timer(1, unit="ns")
+
+    assert int(reg2b.AWVALID.value) == 1, "reg2b must be selected for address 0x14"
+    assert int(reg1.AWVALID.value) == 0, "reg1 should not be selected"
+    assert int(reg2.AWVALID.value) == 0, "reg2 should not be selected"

tests/cocotb/axi4lite/smoke/test_variable_depth_runner.py

@@ -0,0 +1,128 @@
+"""Pytest wrapper launching the AXI4-Lite cocotb smoke test for variable depth."""
+
+from pathlib import Path
+
+import pytest
+
+from peakrdl_busdecoder.cpuif.axi4lite.axi4_lite_cpuif_flat import AXI4LiteCpuifFlat
+
+try:  # pragma: no cover - optional dependency shim
+    from cocotb.runner import get_runner
+except ImportError:  # pragma: no cover
+    from cocotb_tools.runner import get_runner
+
+from tests.cocotb_lib.utils import compile_rdl_and_export, get_verilog_sources
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_axi4lite_variable_depth_1(tmp_path: Path) -> None:
+    """Test AXI4-Lite design with max_decode_depth=1."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=AXI4LiteCpuifFlat,
+        max_decode_depth=1,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "axi4lite_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.axi4lite.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth1.log"),
+        testcase="test_depth_1",
+    )
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_axi4lite_variable_depth_2(tmp_path: Path) -> None:
+    """Test AXI4-Lite design with max_decode_depth=2."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=AXI4LiteCpuifFlat,
+        max_decode_depth=2,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "axi4lite_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.axi4lite.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth2.log"),
+        testcase="test_depth_2",
+    )
+
+
+@pytest.mark.simulation
+@pytest.mark.verilator
+def test_axi4lite_variable_depth_0(tmp_path: Path) -> None:
+    """Test AXI4-Lite design with max_decode_depth=0 (all levels)."""
+    repo_root = Path(__file__).resolve().parents[4]
+
+    module_path, package_path = compile_rdl_and_export(
+        str(repo_root / "tests" / "cocotb_lib" / "variable_depth.rdl"),
+        "variable_depth",
+        tmp_path,
+        cpuif_cls=AXI4LiteCpuifFlat,
+        max_decode_depth=0,
+    )
+
+    sources = get_verilog_sources(
+        module_path,
+        package_path,
+        [repo_root / "hdl-src" / "axi4lite_intf.sv"],
+    )
+
+    runner = get_runner("verilator")
+    build_dir = tmp_path / "sim_build"
+
+    runner.build(
+        sources=sources,
+        hdl_toplevel=module_path.stem,
+        build_dir=build_dir,
+    )
+
+    runner.test(
+        hdl_toplevel=module_path.stem,
+        test_module="tests.cocotb.axi4lite.smoke.test_variable_depth",
+        build_dir=build_dir,
+        log_file=str(tmp_path / "sim_depth0.log"),
+        testcase="test_depth_0",
+    )

tests/cocotb_lib/__init__.py

@@ -0,0 +1,10 @@
+"""Manifest of SystemRDL sources used by the cocotb simulations."""
+
+RDL_CASES: list[tuple[str, str]] = [
+    ("simple.rdl", "simple_test"),
+    ("multiple_reg.rdl", "multi_reg"),
+    ("deep_hierarchy.rdl", "deep_hierarchy"),
+    ("wide_status.rdl", "wide_status"),
+    ("variable_layout.rdl", "variable_layout"),
+    ("asymmetric_bus.rdl", "asymmetric_bus"),
+]

tests/cocotb_lib/handle_utils.py

@@ -0,0 +1,70 @@
+"""Utilities for resolving cocotb signal handles across simulators."""
+
+from __future__ import annotations
+
+from collections.abc import Iterable
+from typing import Any
+
+
+class SignalHandle:
+    """
+    Wrapper that resolves array elements even when the simulator does not expose
+    unpacked arrays through ``handle[idx]``.
+    """
+
+    def __init__(self, dut, name: str) -> None:
+        self._dut = dut
+        self._name = name
+        self._base = getattr(dut, name, None)
+        self._cache: dict[tuple[int, ...], Any] = {}
+
+    def resolve(self, indices: tuple[int, ...]):
+        if not indices:
+            return self._base if self._base is not None else self._lookup(tuple())
+
+        if indices not in self._cache:
+            self._cache[indices] = self._direct_or_lookup(indices)
+        return self._cache[indices]
+
+    def _direct_or_lookup(self, indices: tuple[int, ...]):
+        if self._base is not None:
+            ref = self._base
+            try:
+                for idx in indices:
+                    ref = ref[idx]
+                return ref
+            except (IndexError, TypeError, AttributeError):
+                pass
+
+        return self._lookup(indices)
+
+    def _lookup(self, indices: tuple[int, ...]):
+        suffix = "".join(f"[{idx}]" for idx in indices)
+        path = f"{self._name}{suffix}"
+
+        try:
+            return getattr(self._dut, path)
+        except AttributeError:
+            pass
+
+        errors: list[Exception] = []
+        for extended in (False, True):
+            try:
+                return self._dut._id(path, extended=extended)
+            except (AttributeError, ValueError) as exc:
+                errors.append(exc)
+
+        raise AttributeError(f"Unable to resolve handle '{path}' via dut._id") from errors[-1]
+
+
+def resolve_handle(handle, indices: Iterable[int]):
+    """Resolve either a regular cocotb handle or a ``SignalHandle`` wrapper."""
+    index_tuple = tuple(indices)
+
+    if isinstance(handle, SignalHandle):
+        return handle.resolve(index_tuple)
+
+    ref = handle
+    for idx in index_tuple:
+        ref = ref[idx]
+    return ref

tests/cocotb_lib/protocol_utils.py

@@ -0,0 +1,101 @@
+"""Shared helpers for cocotb smoke tests."""
+
+from __future__ import annotations
+
+import json
+import os
+from collections.abc import Iterable
+from typing import Any
+
+import cocotb
+from cocotb.clock import Clock
+from cocotb.triggers import RisingEdge, Timer
+
+from tests.cocotb_lib.handle_utils import resolve_handle
+
+
+def load_config() -> dict[str, Any]:
+    """Read the JSON payload describing the generated register topology."""
+    payload = os.environ.get("RDL_TEST_CONFIG")
+    if payload is None:
+        raise RuntimeError("RDL_TEST_CONFIG environment variable was not provided")
+    return json.loads(payload)
+
+
+def resolve(handle, indices: Iterable[int]):
+    """Index into hierarchical cocotb handles."""
+    return resolve_handle(handle, indices)
+
+
+def set_value(handle, indices: Iterable[int], value: int) -> None:
+    resolve(handle, indices).value = value
+
+
+def get_int(handle, indices: Iterable[int]) -> int:
+    return int(resolve(handle, indices).value)
+
+
+def all_index_pairs(table: dict[str, dict[str, Any]]):
+    for name, entry in table.items():
+        for idx in entry["indices"]:
+            yield name, idx
+
+
+def find_invalid_address(config: dict[str, Any]) -> int | None:
+    """Return an address outside any master/array span, or None if fully covered."""
+    addr_width = config["address_width"]
+    max_addr = 1 << addr_width
+    ranges: list[tuple[int, int]] = []
+
+    for master in config["masters"]:
+        inst_address = master["inst_address"]
+        inst_size = master["inst_size"]
+        n_elems = 1
+        if master.get("is_array"):
+            for dim in master.get("dimensions", []):
+                n_elems *= dim
+        span = inst_size * n_elems
+        ranges.append((inst_address, inst_address + span))
+
+    ranges.sort()
+
+    cursor = 0
+    for start, end in ranges:
+        if cursor < start:
+            return cursor
+        cursor = max(cursor, end)
+
+    if cursor < max_addr:
+        return cursor
+    return None
+
+
+async def start_clock(clk_handle, period_ns: int = 2) -> None:
+    """Start a simple clock if handle is present."""
+    if clk_handle is None:
+        return
+    clk_handle.value = 0
+    cocotb.start_soon(Clock(clk_handle, period_ns, unit="ns").start())
+    await RisingEdge(clk_handle)
+
+
+async def apb_setup(slave, addr: int, write: bool, data: int, *, strobe_mask: int | None = None) -> None:
+    """APB setup phase helper."""
+    if hasattr(slave, "PPROT"):
+        slave.PPROT.value = 0
+    if hasattr(slave, "PSTRB"):
+        if strobe_mask is None:
+            strobe_mask = (1 << len(slave.PSTRB)) - 1
+        slave.PSTRB.value = strobe_mask
+    slave.PADDR.value = addr
+    slave.PWDATA.value = data
+    slave.PWRITE.value = 1 if write else 0
+    slave.PSEL.value = 1
+    slave.PENABLE.value = 0
+    await Timer(1, unit="ns")
+
+
+async def apb_access(slave) -> None:
+    """APB access phase helper."""
+    slave.PENABLE.value = 1
+    await Timer(1, unit="ns")

tests/cocotb_lib/rdl/asymmetric_bus.rdl

@@ -0,0 +1,105 @@
+regfile port_rf {
+    reg {
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } port_enable[0:0];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } port_speed[3:1];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } port_width[8:4];
+    } control @ 0x0;
+
+    reg {
+        field {
+            sw = r;
+            hw = w;
+            reset = 0x0;
+        } error_count[15:0];
+
+        field {
+            sw = r;
+            hw = w;
+            reset = 0x0;
+        } retry_count[31:16];
+    } counters @ 0x4;
+
+    reg {
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } qos[7:0];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } virtual_channel[9:8];
+    } qos @ 0x8;
+};
+
+addrmap asymmetric_bus {
+    reg {
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } control[3:0];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } id[15:4];
+    } control @ 0x0;
+
+    reg {
+        field {
+            sw = r;
+            hw = w;
+            reset = 0x0;
+        } status_flags[19:0];
+    } status @ 0x4;
+
+    reg {
+        regwidth = 64;
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x00abcdef;
+        } timestamp_low[31:0];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x00123456;
+        } timestamp_high[55:32];
+    } timestamp @ 0x8;
+
+    reg {
+        regwidth = 128;
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x0;
+        } extended_id[63:0];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x1;
+        } parity[64:64];
+    } extended @ 0x10;
+
+    port_rf port[6] @ 0x40 += 0x20;
+};

tests/cocotb_lib/rdl/deep_hierarchy.rdl

@@ -0,0 +1,115 @@
+addrmap deep_hierarchy {
+    regfile context_rf {
+        reg {
+            field {
+                sw = rw;
+                hw = r;
+                reset = 0x1;
+            } enable[7:0];
+
+            field {
+                sw = r;
+                hw = w;
+                onread = rclr;
+                reset = 0x0;
+            } status[15:8];
+
+            field {
+                sw = rw;
+                hw = rw;
+                reset = 0x55;
+            } mode[23:16];
+        } command @ 0x0;
+
+        reg {
+            field {
+                sw = rw;
+                hw = rw;
+                reset = 0x1234;
+            } threshold[15:0];
+        } threshold @ 0x4;
+
+        reg {
+            field {
+                sw = rw;
+                hw = rw;
+                reset = 0x0;
+            } counter[31:0];
+        } counter @ 0x8;
+    };
+
+    regfile engine_rf {
+        context_rf context[3] @ 0x0;
+
+        reg {
+            field {
+                sw = rw;
+                hw = rw;
+                reset = 0x0;
+            } timeout[15:0];
+
+            field {
+                sw = rw;
+                hw = rw;
+                reset = 0x1;
+            } priority[19:16];
+        } config @ 0x30;
+
+        reg {
+            field {
+                sw = r;
+                hw = w;
+                onread = rclr;
+                reset = 0x0;
+            } error[31:0];
+        } error_log @ 0x34;
+    };
+
+    addrmap fabric_slice {
+        engine_rf engines[4] @ 0x0;
+
+        regfile monitor_rf {
+            reg {
+                field {
+                    sw = r;
+                    hw = w;
+                    reset = 0x0;
+                } perf_count[31:0];
+            } perf @ 0x0;
+
+            reg {
+                field {
+                    sw = r;
+                    hw = w;
+                    reset = 0x0;
+                } last_error[31:0];
+            } last_error @ 0x4;
+        };
+
+        monitor_rf monitor @ 0x400;
+
+        reg {
+            field {
+                sw = rw;
+                hw = rw;
+                reset = 0xdeadbeef;
+            } fabric_ctrl[31:0];
+        } fabric_ctrl @ 0x500;
+    };
+
+    fabric_slice slices[2] @ 0x0 += 0x800;
+
+    reg {
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x1;
+        } global_enable[0:0];
+
+        field {
+            sw = rw;
+            hw = rw;
+            reset = 0x4;
+        } debug_level[3:1];
+    } global_control @ 0x1000;
+};

tests/cocotb_lib/rdl/multiple_reg.rdl

@@ -0,0 +1,22 @@
+addrmap multi_reg {
+    reg {
+        field {
+            sw=rw;
+            hw=r;
+        } data[31:0];
+    } reg1 @ 0x0;
+
+    reg {
+        field {
+            sw=r;
+            hw=w;
+        } status[15:0];
+    } reg2 @ 0x4;
+
+    reg {
+        field {
+            sw=rw;
+            hw=r;
+        } control[7:0];
+    } reg3 @ 0x8;
+};

tests/cocotb_lib/rdl/simple.rdl

@@ -0,0 +1,8 @@
+addrmap simple_test {
+    reg {
+        field {
+            sw=rw;
+            hw=r;
+        } data[31:0];
+    } test_reg @ 0x0;
+};