src/ieee754/part_cmp/experiments/gt_combiner.py

   1 from nmigen import Signal, Module, Elaboratable, Mux
   2 from ieee754.part_mul_add.partpoints import PartitionPoints
   3 from ieee754.part_cmp.experiments.eq_combiner import Twomux
   4
   5
   6 # This is similar to EQCombiner, except that for a greater than
   7 # comparison, it needs to deal with both the greater than and equals
   8 # signals from each partition. The signals are combined using a
   9 # cascaded AND/OR to give the following effect:
  10 # When a partition is open, the output is set if either the current
  11 # partition's greater than flag is set, or the current partition's
  12 # equal flag is set AND the previous partition's greater than output
  13 # is true
  14 class GTCombiner(Elaboratable):
  15     def __init__(self, width):
  16         self.width = width
  17         self.mux_input = Signal(reset_less=True)  # right hand side mux input
  18         self.eqs = Signal(width, reset_less=True) # the flags for EQ
  19         self.gts = Signal(width, reset_less=True) # the flags for GT
  20         self.gates = Signal(width-1, reset_less=True)
  21         self.outputs = Signal(width, reset_less=True)
  22
  23     def elaborate(self, platform):
  24         m = Module()
  25         comb = m.d.comb
  26
  27         previnput = self.gts[-1] | (self.eqs[-1] & self.mux_input)
  28         for i in range(self.width-1, 0, -1): # counts down from width-1 to 1
  29             m.submodules["mux{}".format(i)] = mux = Twomux()
  30
  31             comb += mux.ina.eq(previnput)
  32             comb += mux.inb.eq(self.mux_input)
  33             comb += mux.sel.eq(self.gates[i-1])
  34             comb += self.outputs[i].eq(mux.outb)
  35             previnput =  self.gts[i-1] | (self.eqs[i-1] & mux.outa)
  36
  37         comb += self.outputs[0].eq(previnput)
  38
  39         return m
  40
  41     def ports(self):
  42         return [self.eqs, self.gts, self.gates, self.outputs]