src/ieee754/fpdiv/pipeline.py

   1 """IEEE Floating Point Divider Pipeline
   2
   3 Relevant bugreport: http://bugs.libre-riscv.org/show_bug.cgi?id=99
   4
   5 Stack looks like this:
   6
   7 scnorm   - FPDIVSpecialCasesDeNorm ispec FPADDBaseData  ospec FPSCData
   8             StageChain: FPDIVSpecialCasesMod,
   9                         FPAddDeNormMod
  10
  11 pipediv0 - FPDivStages(start=true) ispec FPSCData       ospec FPDivStage0Data
  12             StageChain: FPDivStage0Mod,
  13                         FPDivStage1Mod,
  14                         ...
  15                         FPDivStage1Mod
  16
  17 pipediv1 - FPDivStages()           ispec FPDivStage0Data ospec FPDivStage0Data
  18             StageChain: FPDivStage1Mod,
  19                         ...
  20                         FPDivStage1Mod
  21 ...
  22 ...
  23
  24 pipediv5 - FPDivStages(end=true    ispec FPDivStage0Data ospec FPAddStage1Data
  25             StageChain: FPDivStage1Mod,
  26                         ...
  27                         FPDivStage1Mod,
  28                         FPDivStage2Mod
  29
  30 normpack - FPNormToPack            ispec FPAddStage1Data ospec FPPackData
  31             StageChain: Norm1ModSingle,
  32                         RoundMod,
  33                         CorrectionsMod,
  34                         PackMod
  35
  36 the number of combinatorial StageChains (n_combinatorial_stages) in
  37 FPDivStages is an argument arranged to get the length of the whole
  38 pipeline down to sane numbers.
  39 """
  40
  41 from nmigen import Module
  42 from nmigen.cli import main, verilog
  43
  44 from nmutil.singlepipe import ControlBase
  45 from nmutil.concurrentunit import ReservationStations, num_bits
  46
  47 from ieee754.fpcommon.getop import FPADDBaseData
  48 from ieee754.fpcommon.denorm import FPSCData
  49 from ieee754.fpcommon.pack import FPPackData
  50 from ieee754.fpcommon.normtopack import FPNormToPack
  51 from .specialcases import FPDIVSpecialCasesDeNorm
  52 from .divstages import FPDivStages
  53
  54
  55
  56 class FPDIVBasePipe(ControlBase):
  57     def __init__(self, width, id_wid):
  58         ControlBase.__init__(self)
  59         self.pipestart = FPDIVSpecialCasesDeNorm(width, id_wid)
  60         pipechain = []
  61         n_stages = 6 # TODO
  62         n_combinatorial_stages = 2 # TODO
  63         for i in range(n_stages):
  64             begin = i == 0 # needs to convert input from pipestart ospec
  65             end = i == n_stages - 1 # needs to convert output to pipeend ispec
  66             pipechain.append(FPDivStages(width, id_wid,
  67                                          n_combinatorial_stages,
  68                                          begin, end))
  69         self.pipechain = pipechain
  70         self.pipeend = FPNormToPack(width, id_wid)
  71
  72         self._eqs = self.connect([self.pipestart] + pipechain + [self.pipeend])
  73
  74     def elaborate(self, platform):
  75         m = ControlBase.elaborate(self, platform)
  76         m.submodules.scnorm = self.pipestart
  77         for i, p in enumerate(self.pipechain):
  78             setattr(m.submodules, "pipediv%d" % i, p)
  79         m.submodules.normpack = self.pipeend
  80         m.d.comb += self._eqs
  81         return m
  82
  83
  84 class FPDIVMuxInOut(ReservationStations):
  85     """ Reservation-Station version of FPDIV pipeline.
  86
  87         * fan-in on inputs (an array of FPADDBaseData: a,b,mid)
  88         * N-stage divider pipeline
  89         * fan-out on outputs (an array of FPPackData: z,mid)
  90
  91         Fan-in and Fan-out are combinatorial.
  92     """
  93     def __init__(self, width, num_rows):
  94         self.width = width
  95         self.id_wid = num_bits(width)
  96         self.alu = FPDIVBasePipe(width, self.id_wid)
  97         ReservationStations.__init__(self, num_rows)
  98
  99     def i_specfn(self):
 100         return FPADDBaseData(self.width, self.id_wid)
 101
 102     def o_specfn(self):
 103         return FPPackData(self.width, self.id_wid)