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
   4 class Combiner(Elaboratable):
   5     def __init__(self):
   6         self.ina = Signal()
   7         self.inb = Signal()
   8         self.sel = Signal()
   9         self.outa = Signal()
  10         self.outb = Signal()
  11     def elaborate(self, platform):
  12         m = Module()
  13         comb = m.d.comb
  14
  15         comb += self.outa.eq(Mux(self.sel, self.inb, self.ina))
  16         comb += self.outb.eq(self.sel & self.ina)
  17
  18         return m
  19
  20 # This is similar to EQCombiner, except that for a greater than
  21 # comparison, it needs to deal with both the greater than and equals
  22 # signals from each partition. The signals are combined using a
  23 # cascaded AND/OR to give the following effect:
  24 # When a partition is open, the output is set if either the current
  25 # partition's greater than flag is set, or the current partition's
  26 # equal flag is set AND the previous partition's greater than output
  27 # is true
  28 class GTCombiner(Elaboratable):
  29     def __init__(self, width):
  30         self.width = width
  31         self.mux_input = Signal(reset_less=True)  # right hand side mux input
  32         self.eqs = Signal(width, reset_less=True) # the flags for EQ
  33         self.gts = Signal(width, reset_less=True) # the flags for GT
  34         self.gates = Signal(width-1, reset_less=True)
  35         self.outputs = Signal(width, reset_less=True)
  36
  37     def elaborate(self, platform):
  38         m = Module()
  39         comb = m.d.comb
  40
  41         previnput = self.gts[-1] | (self.eqs[-1] & self.mux_input)
  42         for i in range(self.width-1, 0, -1): # counts down from width-1 to 1
  43             m.submodules["mux%d" % i] = mux = Combiner()
  44
  45             comb += mux.ina.eq(previnput)
  46             comb += mux.inb.eq(self.mux_input)
  47             comb += mux.sel.eq(self.gates[i-1])
  48             comb += self.outputs[i].eq(mux.outb)
  49             previnput = self.gts[i-1] | (self.eqs[i-1] & mux.outa)
  50
  51         comb += self.outputs[0].eq(previnput)
  52
  53         return m
  54
  55     def ports(self):
  56         return [self.eqs, self.gts, self.gates, self.outputs]