Refactor cpuif classes to use Interface abstraction (#14)

* Initial plan

* Refactor cpuif classes to use Interface abstraction

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Fix type annotation consistency in Interface.signal()

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Add runtime validation and documentation for indexer types

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Remove unused variable in SVInterface.signal()

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Fix master port directions in APB3 and APB4 flat interfaces

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Fix AXI4LiteCpuifFlat and apply code formatting

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* PSELx -> PSEL

* cleanup marker warnings

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

src/peakrdl_busdecoder/cpuif/axi4lite/axi4lite_interface.py

@@ -0,0 +1,84 @@
+"""AXI4-Lite-specific interface implementations."""
+
+from systemrdl.node import AddressableNode
+
+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 [{self.cpuif.addr_width - 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 [{self.cpuif.addr_width - 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)}",
+        ]