src/soc/fu/alu/output_stage.py

   1 # This stage is intended to handle the gating of carry and overflow
   2 # out, summary overflow generation, and updating the condition
   3 # register
   4 from nmigen import (Module, Signal, Cat, Repl)
   5 from soc.fu.alu.pipe_data import ALUInputData, ALUOutputData
   6 from soc.fu.common_output_stage import CommonOutputStage
   7 from ieee754.part.partsig import PartitionedSignal
   8 from soc.decoder.power_enums import MicrOp
   9
  10
  11 class ALUOutputStage(CommonOutputStage):
  12
  13     def ispec(self):
  14         return ALUOutputData(self.pspec)
  15
  16     def ospec(self):
  17         return ALUOutputData(self.pspec)
  18
  19     def elaborate(self, platform):
  20         m = super().elaborate(platform)
  21         comb = m.d.comb
  22         op = self.i.ctx.op
  23         xer_so_i, xer_ov_i = self.i.xer_so.data, self.i.xer_ov.data
  24         xer_so_o, xer_ov_o = self.o.xer_so, self.o.xer_ov
  25
  26         # copy overflow and sticky-overflow.  indicate to CompALU if they
  27         # are actually required (oe enabled/set) otherwise the CompALU
  28         # can (will) ignore them.
  29         oe = Signal(reset_less=True)
  30         comb += oe.eq(op.oe.oe & op.oe.ok)
  31         with m.If(oe):
  32             # XXX see https://bugs.libre-soc.org/show_bug.cgi?id=319#c5
  33             comb += xer_so_o.data.eq(xer_so_i[0] | xer_ov_i[0]) # SO
  34             comb += xer_so_o.ok.eq(1)
  35             comb += xer_ov_o.data.eq(xer_ov_i)
  36             comb += xer_ov_o.ok.eq(1) # OV/32 is to be set
  37
  38         return m