src/nmutil/byterev.py

   1 # SPDX-License-Identifier: LGPL-3-or-later
   2 """
   3     This work is funded through NLnet under Grant 2019-02-012
   4
   5     License: LGPLv3+
   6 """
   7
   8 from nmigen import Signal, Cat
   9
  10 # TODO: turn this into a module?
  11
  12
  13 def byte_reverse(m, name, data, length):
  14     """byte_reverse: unlike nmigen word_select this takes a dynamic length
  15
  16     nmigen Signal.word_select may only take a fixed length.  we need
  17     bigendian byte-reverse, half-word reverse, word and dword reverse.
  18     """
  19     comb = m.d.comb
  20     data_r = Signal.like(data, name=name)
  21
  22     # if length is a static integer, we do not require a Case statement
  23     if isinstance(length, int):
  24         j = length
  25         rev = []
  26         for i in range(j):
  27             dest = data_r.word_select(i, 8)
  28             rev.append(data.word_select(j-1-i, 8))
  29         comb += data_r.eq(Cat(*rev))
  30         return data_r
  31
  32     # Switch statement needed: dynamic length had better be = 1,2,4 or 8
  33     with m.Switch(length):
  34         for j in [1, 2, 4, 8]:
  35             with m.Case(j):
  36                 rev = []
  37                 for i in range(j):
  38                     rev.append(data.word_select(j-1-i, 8))
  39                 comb += data_r.eq(Cat(*rev))
  40     return data_r