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
  11
  12 def byte_reverse(m, name, data, length):
  13     """byte_reverse: unlike nmigen word_select this takes a dynamic length
  14
  15     nmigen Signal.word_select may only take a fixed length.  we need
  16     bigendian byte-reverse, half-word reverse, word and dword reverse.
  17     """
  18     comb = m.d.comb
  19     data_r = Signal.like(data, name=name)
  20
  21     # if length is a static integer, we do not require a Case statement
  22     if isinstance(length, int):
  23         j = length
  24         rev = []
  25         for i in range(j):
  26             dest = data_r.word_select(i, 8)
  27             rev.append(data.word_select(j-1-i, 8))
  28         comb += data_r.eq(Cat(*rev))
  29         return data_r
  30
  31     # Switch statement needed: dynamic length had better be = 1,2,4 or 8
  32     with m.Switch(length):
  33         for j in [1, 2, 4, 8]:
  34             with m.Case(j):
  35                 rev = []
  36                 for i in range(j):
  37                     rev.append(data.word_select(j-1-i, 8))
  38                 comb += data_r.eq(Cat(*rev))
  39     return data_r