src/ieee754/part_cmp/gt_combiner.py

   1 from nmigen import Signal, Module, Elaboratable, Mux
   2
   3
   4 class Combiner(Elaboratable):
   5
   6     def __init__(self):
   7         self.ina = Signal()
   8         self.inb = Signal()
   9         self.sel = Signal()
  10         self.outa = Signal()
  11         self.outb = Signal()
  12
  13     def elaborate(self, platform):
  14         m = Module()
  15         comb = m.d.comb
  16
  17         comb += self.outa.eq(Mux(self.sel, self.inb, self.ina))
  18         comb += self.outb.eq(self.ina)
  19
  20         return m
  21
  22 # This is similar to EQCombiner, except that for a greater than
  23 # comparison, it needs to deal with both the greater than and equals
  24 # signals from each partition. The signals are combined using a
  25 # cascaded AND/OR to give the following effect:
  26 # When a partition is open, the output is set if either the current
  27 # partition's greater than flag is set, or the current partition's
  28 # equal flag is set AND the previous partition's greater than output
  29 # is true
  30
  31
  32 class GTCombiner(Elaboratable):
  33
  34     def __init__(self, width):
  35         self.width = width
  36
  37         # These two signals allow this module to do more than just a
  38         # partitioned greater than comparison.
  39         # - If aux_input is set to 0 and gt_en is set to 1, then this
  40         #   module performs a partitioned greater than comparision
  41         # - If aux_input is set to 1 and gt_en is set to 0, then this
  42         #   module is functionally equivalent to the eq_combiner
  43         #   module.
  44         # - If aux_input is set to 1 and gt_en is set to 1, then this
  45         #   module performs a partitioned greater than or equals
  46         #   comparison
  47         self.aux_input = Signal(reset_less=True)  # right hand side mux input
  48         self.gt_en = Signal(reset_less=True)      # enable or disable gt signal
  49
  50         self.eqs = Signal(width, reset_less=True)  # the flags for EQ
  51         self.gts = Signal(width, reset_less=True)  # the flags for GT
  52         self.gates = Signal(width-1, reset_less=True)
  53         self.outputs = Signal(width, reset_less=True)
  54
  55     def elaborate(self, platform):
  56         m = Module()
  57         comb = m.d.comb
  58
  59         previnput = (self.gts[0] & self.gt_en) | (self.eqs[0] & self.aux_input)
  60
  61         for i in range(self.width-1):
  62             m.submodules["mux%d" % i] = mux = Combiner()
  63
  64             comb += mux.ina.eq(previnput)
  65             comb += mux.inb.eq(self.aux_input)
  66             comb += mux.sel.eq(self.gates[i])
  67             comb += self.outputs[i].eq(mux.outb)
  68             previnput = (self.gts[i+1] & self.gt_en) | \
  69                         (self.eqs[i+1] & mux.outa)
  70
  71         comb += self.outputs[-1].eq(previnput)
  72
  73         return m
  74
  75     def ports(self):
  76         return [self.eqs, self.gts, self.gates, self.outputs,
  77                 self.gt_en, self.aux_input]