# however should not gate the carry or overflow, that's up to the
# output stage
+# License: LGPLv3+
+# Copyright (C) 2020 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
# Copyright (C) 2020 Michael Nolan <mtnolan2640@gmail.com>
+# (michael: note that there are multiple copyright holders)
+
from nmigen import (Module, Signal, Cat, Repl, Mux, Const)
from nmutil.pipemodbase import PipeModBase
-from nmutil.extend import exts
+from nmutil.extend import exts, extz
from soc.fu.alu.pipe_data import ALUInputData, ALUOutputData
from ieee754.part.partsig import PartitionedSignal
from soc.decoder.power_enums import MicrOp
# convenience variables
cry_o, o, cr0 = self.o.xer_ca, self.o.o, self.o.cr0
- ov_o = self.o.xer_ov
+ xer_so_i, ov_o = self.i.xer_so, self.o.xer_ov
a, b, cry_i, op = self.i.a, self.i.b, self.i.xer_ca, self.i.ctx.op
# get L-field for OP_CMP
a_i = Signal.like(a)
b_i = Signal.like(b)
- with m.If(is_32bit):
- comb += a_i.eq(exts(a, 32, 64))
- comb += b_i.eq(exts(b, 32, 64))
+ with m.If(op.insn_type == MicrOp.OP_CMP): # another temporary hack
+ comb += a_i.eq(a) # reaaaally need to move CMP
+ comb += b_i.eq(b) # into trap pipeline
+ with m.Elif(is_32bit):
+ with m.If(op.is_signed):
+ comb += a_i.eq(exts(a, 32, 64))
+ comb += b_i.eq(exts(b, 32, 64))
+ with m.Else():
+ comb += a_i.eq(extz(a, 32, 64))
+ comb += b_i.eq(extz(b, 32, 64))
with m.Else():
comb += a_i.eq(a)
comb += b_i.eq(b)
#### CMP, CMPL v3.0B p85-86
with m.Case(MicrOp.OP_CMP):
+ a_n = Signal(64) # temporary - inverted a
+ tval = Signal(5)
+ a_lt = Signal()
+ carry_32 = Signal()
+ carry_64 = Signal()
+ zerolo = Signal()
+ zerohi = Signal()
+ msb_a = Signal()
+ msb_b = Signal()
+ newcrf = Signal(4)
+
# this is supposed to be inverted (b-a, not a-b)
- # however we have a trick: instead of adding either 2x 64-bit
- # MUXes to invert a and b, or messing with a 64-bit output,
- # swap +ve and -ve test in the *output* stage using an XOR gate
- comb += o.data.eq(add_o[1:-1])
- comb += o.ok.eq(0) # use o.data but do *not* actually output
+ comb += a_n.eq(~a) # sigh a gets inverted
+ comb += carry_32.eq(add_o[33] ^ a[32] ^ b[32])
+ comb += carry_64.eq(add_o[65])
+
+ comb += zerolo.eq(~((a_n[0:32] ^ b[0:32]).bool()))
+ comb += zerohi.eq(~((a_n[32:64] ^ b[32:64]).bool()))
+
+ with m.If(zerolo & (is_32bit | zerohi)):
+ # values are equal
+ comb += tval[2].eq(1)
+ with m.Else():
+ comb += msb_a.eq(Mux(is_32bit, a_n[31], a_n[63]))
+ comb += msb_b.eq(Mux(is_32bit, b[31], b[63]))
+ C0 = Const(0, 1)
+ with m.If(msb_a != msb_b):
+ # Subtraction might overflow, but
+ # comparison is clear from MSB difference.
+ # for signed, 0 is greater; for unsigned, 1 is greater
+ comb += tval.eq(Cat(msb_a, msb_b, C0, msb_b, msb_a))
+ with m.Else():
+ # Subtraction cannot overflow since MSBs are equal.
+ # carry = 1 indicates RA is smaller (signed or unsigned)
+ comb += a_lt.eq(Mux(is_32bit, carry_32, carry_64))
+ comb += tval.eq(Cat(~a_lt, a_lt, C0, ~a_lt, a_lt))
+ comb += cr0.data[0:2].eq(Cat(xer_so_i[0], tval[2]))
+ with m.If(op.is_signed):
+ comb += cr0.data[2:4].eq(tval[3:5])
+ with m.Else():
+ comb += cr0.data[2:4].eq(tval[0:2])
+ comb += cr0.ok.eq(1)
###################
#### add v3.0B p67, p69-72
###### sticky overflow and context, both pass-through #####
- comb += self.o.xer_so.data.eq(self.i.xer_so)
+ comb += self.o.xer_so.data.eq(xer_so_i)
comb += self.o.ctx.eq(self.i.ctx)
return m
projects / soc.git / blobdiff