src/nmutil/grev.py

   1 # SPDX-License-Identifier: LGPL-3-or-later
   2 # See Notices.txt for copyright information
   3
   4 from nmigen.hdl.ast import Signal
   5 from nmigen.hdl.dsl import Module
   6 from nmigen.hdl.ir import Elaboratable
   7
   8
   9 class GRev(Elaboratable):
  10     def __init__(self, log2_width):
  11         assert isinstance(log2_width, int)
  12         self.log2_width = log2_width
  13         self.width = 1 << log2_width
  14
  15         self.input = Signal(self.width)
  16         self.chunk_sizes = Signal(log2_width)
  17
  18         def step(i):
  19             return Signal(self.width, name=f"step{i}")
  20         self._steps = [step(i) for i in range(log2_width)]
  21
  22         self.output = Signal(self.width)
  23
  24     def elaborate(self, platform):
  25         m = Module()
  26         for i, step_o in enumerate(self._steps):
  27             step_i = self.input if i == 0 else self._steps[i - 1]
  28             chunk_size = 1 << i
  29             with m.If(self.chunk_sizes[i]):
  30                 for j in range(self.width):
  31                     m.d.comb += step_o[j].eq(step_i[j ^ chunk_size])
  32             with m.Else():
  33                 m.d.comb += step_o.eq(step_i)
  34         m.d.comb += self.output.eq(self._steps[-1])
  35         return m