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 length is a static integer, we do not require a Case statement
  20     if isinstance(length, int):
  21         j = length
  22         rev = []
  23         for i in range(j):
  24             dest = data_r.word_select(i, 8)
  25             rev.append(data.word_select(j-1-i, 8))
  26         comb += data_r.eq(Cat(*rev))
  27         return data_r
  28
  29     # Switch statement needed: dynamic length had better be = 1,2,4 or 8
  30     with m.Switch(length):
  31         for j in [1,2,4,8]:
  32             with m.Case(j):
  33                 rev = []
  34                 for i in range(j):
  35                     rev.append(data.word_select(j-1-i, 8))
  36                 comb += data_r.eq(Cat(*rev))
  37     return data_r
  38