src/ieee754/fpmul/pipeline.py

   1 """IEEE754 Floating Point Multiplier Pipeline
   2
   3 Copyright (C) 2019 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
   4 Copyright (C) 2019 Jake Lifshay
   5
   6 Relevant bugreport: http://bugs.libre-riscv.org/show_bug.cgi?id=77
   7
   8 Stack looks like this:
   9
  10 * scnorm    - FPMulSpecialCasesDeNorm
  11 * mulstages - FPMulstages
  12 * normpack  - FPNormToPack
  13
  14 scnorm   - FPDIVSpecialCasesDeNorm ispec FPBaseData
  15 ------                             ospec FPSCData
  16
  17                 StageChain: FPMULSpecialCasesMod,
  18                             FPAddDeNormMod
  19                             FPAlignModSingle
  20
  21 mulstages - FPMulStages            ispec FPSCData
  22 ---------                          ospec FPPostCalcData
  23
  24                 StageChain: FPMulStage0Mod
  25                             FPMulStage1Mod
  26
  27 normpack  - FPNormToPack           ispec FPPostCalcData
  28 --------                           ospec FPPackData
  29
  30                 StageChain: Norm1ModSingle,
  31                             RoundMod,
  32                             CorrectionsMod,
  33                             PackMod
  34
  35 This is the *current* stack.  FPMulStage0Mod is where the actual
  36 mantissa multiply takes place, which in the case of FP64 is a
  37 single (massive) combinatorial block.  This can be fixed by using
  38 a multi-stage fixed-point multiplier pipeline, which was implemented
  39 in #60: http://bugs.libre-riscv.org/show_bug.cgi?id=60
  40
  41 """
  42
  43 from nmigen import Module
  44 from nmigen.cli import main, verilog
  45
  46 from nmutil.singlepipe import ControlBase
  47 from nmutil.concurrentunit import ReservationStations, num_bits
  48
  49 from ieee754.fpcommon.basedata import FPBaseData
  50 from ieee754.fpcommon.denorm import FPSCData
  51 from ieee754.fpcommon.pack import FPPackData
  52 from ieee754.fpcommon.normtopack import FPNormToPack
  53 from .specialcases import FPMulSpecialCasesDeNorm
  54 from .mulstages import FPMulStages
  55 from ieee754.pipeline import PipelineSpec
  56
  57
  58 class FPMULBasePipe(ControlBase):
  59     def __init__(self, pspec):
  60         ControlBase.__init__(self)
  61         self.pipe1 = FPMulSpecialCasesDeNorm(pspec)
  62         self.pipe2 = FPMulStages(pspec)
  63         self.pipe3 = FPNormToPack(pspec)
  64
  65         self._eqs = self.connect([self.pipe1, self.pipe2, self.pipe3])
  66
  67     def elaborate(self, platform):
  68         m = ControlBase.elaborate(self, platform)
  69         m.submodules.scnorm = self.pipe1
  70         m.submodules.mulstages = self.pipe2
  71         m.submodules.normpack = self.pipe3
  72         m.d.comb += self._eqs
  73         return m
  74
  75
  76 class FPMULMuxInOut(ReservationStations):
  77     """ Reservation-Station version of FPMUL pipeline.
  78
  79         * fan-in on inputs (an array of FPBaseData: a,b,mid)
  80         * 2-stage multiplier pipeline
  81         * fan-out on outputs (an array of FPPackData: z,mid)
  82
  83         Fan-in and Fan-out are combinatorial.
  84     """
  85
  86     def __init__(self, width, num_rows, op_wid=0):
  87         self.id_wid = num_bits(num_rows)
  88         self.op_wid = op_wid
  89         self.pspec = PipelineSpec(width, self.id_wid, self.op_wid)
  90         self.alu = FPMULBasePipe(self.pspec)
  91         ReservationStations.__init__(self, num_rows)