From 564852d8f2bff379b4f9d99993ac609e2b2389b9 Mon Sep 17 00:00:00 2001 From: Luke Kenneth Casson Leighton Date: Sat, 30 Jan 2021 13:10:16 +0000 Subject: [PATCH 1/1] add SVP64CRExtra class to PowerDecoder2, turns 3-bit CR into 7-bit plus isvec --- src/soc/decoder/power_decoder2.py | 46 ++++++++++++++++++++++++++++++- 1 file changed, 45 insertions(+), 1 deletion(-) diff --git a/src/soc/decoder/power_decoder2.py b/src/soc/decoder/power_decoder2.py index 88121f0e..c3ef17f6 100644 --- a/src/soc/decoder/power_decoder2.py +++ b/src/soc/decoder/power_decoder2.py @@ -145,7 +145,7 @@ class SVP64RegExtra(SVP64ExtraSpec): self.isvec = Signal(1) # reg is marked as vector if true def elaborate(self, platform): - m = super().elaborate(platform) + m = super().elaborate(platform) # select required EXTRA2/3 comb = m.d.comb # first get the spec. if not changed it's "scalar identity behaviour" @@ -169,6 +169,50 @@ class SVP64RegExtra(SVP64ExtraSpec): return m +class SVP64CRExtra(SVP64ExtraSpec): + """SVP64CRExtra - decodes SVP64 Extra fields to determine CR extension + + incoming 3-bit CR is turned into a 7-bit and marked as scalar/vector + depending on info in one of the positions in the EXTRA field. + + yes, really, 128 CRs. INT is 128, FP is 128, therefore CRs are 128. + + designed so that "no change" to the 3-bit CR register number occurs if + SV either does not apply or the relevant EXTRA2/3 field bits are zero. + + see https://libre-soc.org/openpower/sv/svp64/appendix + """ + def __init__(self): + SVP64ExtraSpec.__init__(self) + self.cr_in = Signal(3) # incoming CR number (3 bits, BA[2:5], BFA) + self.cr_out = Signal(7) # extra-augmented CR output (7 bits) + self.isvec = Signal(1) # reg is marked as vector if true + + def elaborate(self, platform): + m = super().elaborate(platform) # select required EXTRA2/3 + comb = m.d.comb + + # first get the spec. if not changed it's "scalar identity behaviour" + # which is zero which is ok. + spec = self.spec + + # now decode it. bit 2 is "scalar/vector". note that spec could be zero + # from above, which (by design) has the effect of "no change", below. + + # simple: isvec is top bit of spec + comb += self.isvec.eq(spec[2]) + + # decode vector differently from scalar, insert bits 0 and 1 accordingly + with m.If(self.isvec): + # Vector: shifted up, extra in LSBs (CR << 4) | (spec[0:1] << 2) + comb += self.cr_out.eq(Cat(Const(0, 2), spec[:2], self.cr_in)) + with m.Else(): + # Scalar: not shifted up, extra in MSBs CR | (spec[0:1] << 3) + comb += self.cr_out.eq(Cat(self.cr_in, spec[:2])) + + return m + + class DecodeA(Elaboratable): """DecodeA from instruction -- 2.30.2