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src/peakrdl_regblock/readback/generators.py

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+from typing import TYPE_CHECKING, List
+
+from ..forloop_generator import RDLForLoopGenerator, LoopBody
+
+if TYPE_CHECKING:
+    from ..exporter import RegblockExporter
+    from systemrdl.node import RegNode
+
+class ReadbackLoopBody(LoopBody):
+    def __init__(self, dim: int, iterator: str, i_type: str) -> None:
+        super().__init__(dim, iterator, i_type)
+        self.n_regs = 0
+
+    def __str__(self) -> str:
+        # replace $i#sz token when stringifying
+        s = super().__str__()
+        token = f"${self.iterator}sz"
+        s = s.replace(token, str(self.n_regs))
+        return s
+
+class ReadbackAssignmentGenerator(RDLForLoopGenerator):
+    i_type = "genvar"
+    loop_body_cls = ReadbackLoopBody
+
+    def __init__(self, exp:'RegblockExporter') -> None:
+        super().__init__()
+        self.exp = exp
+
+        # The readback array collects all possible readback values into a flat
+        # array. The array width is equal to the CPUIF bus width. Each entry in
+        # the array represents an aligned read access.
+        self.current_offset = 0
+        self.start_offset_stack = [] # type: List[int]
+        self.dim_stack = [] # type: List[int]
+
+    @property
+    def current_offset_str(self) -> str:
+        """
+        Derive a string that represents the current offset being assigned.
+        This consists of:
+        - The current integer offset
+        - multiplied index of any enclosing loop
+
+        The integer offset from "current_offset" is static and is monotonically
+        incremented as more register assignments are processed.
+
+        The component of the offset from loops is added by multiplying the current
+        loop index by the loop size.
+        Since the loop's size is not known at this time, it is emitted as a
+        placeholder token like: $i0sz, $i1sz, $i2sz, etc
+        These tokens can be replaced once the loop body has been completed and the
+        size of its contents is known.
+        """
+        offset_parts = []
+        for i in range(self._loop_level):
+            offset_parts.append(f"i{i}*$i{i}sz")
+        offset_parts.append(str(self.current_offset))
+        return " + ".join(offset_parts)
+
+    def enter_Reg(self, node: 'RegNode') -> None:
+        # TODO: account for smaller regs that are not aligned to the bus width
+        #   - offset the field bit slice as appropriate
+        #   - do not always increment the current offset
+        if node.has_sw_readable:
+            current_bit = 0
+            rd_strb = f"({self.exp.dereferencer.get_access_strobe(node)} && !decoded_req_is_wr)"
+            # Fields are sorted by ascending low bit
+            for field in node.fields():
+                if field.is_sw_readable:
+                    # insert reserved assignment before if needed
+                    if field.low != current_bit:
+                        self.add_content(f"assign readback_array[{self.current_offset_str}][{field.low-1}:{current_bit}] = '0;")
+
+                    if field.msb < field.lsb:
+                        # Field gets bitswapped since it is in [low:high] orientation
+                        value = f"{{<<{{{self.exp.dereferencer.get_value(field)}}}}}"
+                    else:
+                        value = self.exp.dereferencer.get_value(field)
+
+                    self.add_content(f"assign readback_array[{self.current_offset_str}][{field.high}:{field.low}] = {rd_strb} ? {value} : '0;")
+
+                    current_bit = field.high + 1
+
+            # Insert final reserved assignment if needed
+            bus_width = self.exp.cpuif.data_width
+            if current_bit < bus_width:
+                self.add_content(f"assign readback_array[{self.current_offset_str}][{bus_width-1}:{current_bit}] = '0;")
+
+            self.current_offset += 1
+
+    def push_loop(self, dim: int) -> None:
+        super().push_loop(dim)
+        self.start_offset_stack.append(self.current_offset)
+        self.dim_stack.append(dim)
+
+    def pop_loop(self) -> None:
+        start_offset = self.start_offset_stack.pop()
+        dim = self.dim_stack.pop()
+
+        # Number of registers enclosed in this loop
+        n_regs = self.current_offset - start_offset
+        self.current_loop.n_regs = n_regs # type: ignore
+
+        super().pop_loop()
+
+        # Advance current scope's offset to account for loop's contents
+        self.current_offset = start_offset + n_regs * dim