src/nmutil/byterev.py

   1 """
   2     This work is funded through NLnet under Grant 2019-02-012
   3
   4     License: LGPLv3+
   5 """
   6
   7 from nmigen import Signal, Cat
   8
   9 # TODO: turn this into a module
  10 def byte_reverse(m, name, data, length):
  11     """byte_reverse: unlike nmigen word_select this takes a dynamic length
  12
  13     nmigen Signal.word_select may only take a fixed length.  we need
  14     bigendian byte-reverse, half-word reverse, word and dword reverse.
  15     """
  16     comb = m.d.comb
  17     data_r = Signal.like(data, name=name)
  18
  19     if isinstance(length, int):
  20         j = length
  21         rev = []
  22         for i in range(j):
  23             dest = data_r.word_select(i, 8)
  24             rev.append(data.word_select(j-1-i, 8))
  25         comb += data_r.eq(Cat(*rev))
  26         return data_r
  27
  28     with m.Switch(length):
  29         for j in [1,2,4,8]:
  30             with m.Case(j):
  31                 rev = []
  32                 for i in range(j):
  33                     rev.append(data.word_select(j-1-i, 8))
  34                 comb += data_r.eq(Cat(*rev))
  35     return data_r
  36
  37