Initial Commit - Forked from PeakRDL-regblock @ a440cc19769069be831d267505da4f3789a26695

docs/udps/extended_swacc.rst

@@ -0,0 +1,49 @@
+.. _extended_swacc:
+
+Read/Write-specific swacc
+=========================
+
+SystemRDL defines the ``swacc`` property, but it does not distinguish between
+read and write operations - it is asserted on *all* software accesses.
+Similarly, the spec defines ``swmod`` which gets asserted on software writes,
+but can also get asserted if the field has on-read side-effects.
+
+What if you just wanted a plain and simple strobe that is asserted when software
+reads or writes a field? The ``rd_swacc`` and ``wr_swacc`` UDPs provide this
+functionality.
+
+
+Properties
+----------
+These UDP definitions, along with others supported by PeakRDL-regblock can be
+enabled by compiling the following file along with your design:
+:download:`regblock_udps.rdl <../../hdl-src/regblock_udps.rdl>`.
+
+.. describe:: rd_swacc
+
+    If true, infers an output signal ``hwif_out..rd_swacc`` that is asserted
+    when accessed by a software read operation. The output signal is asserted
+    on the same clock cycle that the field is being sampled during the software
+    read operation.
+
+    .. wavedrom::
+
+        {"signal": [
+            {"name": "clk",                "wave": "p...."},
+            {"name": "hwif_in..next",      "wave": "x.=x.", "data": ["D"]},
+            {"name": "hwif_out..rd_swacc", "wave": "0.10."}
+        ]}
+
+
+.. describe:: wr_swacc
+
+    If true, infers an output signal ``hwif_out..wr_swacc`` that is asserted
+    as the field is being modified by a software write operation.
+
+    .. wavedrom::
+
+        {"signal": [
+            {"name": "clk",                "wave": "p....."},
+            {"name": "hwif_out..value",    "wave": "=..=..", "data": ["old", "new"]},
+            {"name": "hwif_out..wr_swacc", "wave": "0.10.."}
+        ]}