src/ieee754/part_cmp/ripple.py

   1 # need to ripple the starting LSB of each partition up through the
   2 # rest of the partition.  a Mux on the partition gate therefore selects
   3 # either the current "thing" being propagated, or, if the gate is set open,
   4 # will select the current bit from the input.
   5 #
   6 # this is actually a useful function, it's one of "set before first" or
   7 # "set after first" from vector predication processing.
   8
   9 from nmigen import Signal, Module, Elaboratable, Mux
  10
  11
  12 class RippleLSB(Elaboratable):
  13     def __init__(self, width):
  14         self.width = width
  15         self.results_in = Signal(width, reset_less=True)
  16         self.gates = Signal(width-1, reset_less=True)
  17
  18         self.output = Signal(width, reset_less=True)
  19
  20     def elaborate(self, platform):
  21         m = Module()
  22         comb = m.d.comb
  23         width = self.width
  24
  25         current_result = self.results_in[0]
  26         comb += self.output[0].eq(current_result)
  27
  28         for i in range(width-1):
  29             cur = Signal(name="cur%d" % i)
  30             comb += cur.eq(current_result)
  31             current_result = Mux(self.gates[i], self.results_in[i+1], cur)
  32             comb += self.output[i+1].eq(current_result)
  33
  34         return m