src/ieee754/fpdiv/div0.py

   1 """IEEE754 Floating Point Divider
   2
   3 Relevant bugreport: http://bugs.libre-riscv.org/show_bug.cgi?id=99
   4 """
   5
   6 from nmigen import Module, Signal, Cat, Elaboratable
   7 from nmigen.cli import main, verilog
   8
   9 from ieee754.fpcommon.fpbase import (FPNumBaseRecord, Overflow)
  10 from ieee754.fpcommon.fpbase import FPState
  11 from ieee754.fpcommon.denorm import FPSCData
  12 from ieee754.fpcommon.getop import FPPipeContext
  13
  14
  15 # TODO: delete (replace by DivPipeCoreInputData)
  16 class FPDivStage0Data:
  17
  18     def __init__(self, width, pspec):
  19         self.z = FPNumBaseRecord(width, False)
  20         self.out_do_z = Signal(reset_less=True)
  21         self.oz = Signal(width, reset_less=True)
  22
  23         self.ctx = FPPipeContext(width, pspec) # context: muxid, operator etc.
  24         self.muxid = self.ctx.muxid             # annoying. complicated.
  25
  26         # TODO: here is where Q and R would be put, and passed
  27         # down to Stage1 processing.
  28
  29         mw = (self.z.m_width)*2 - 1 + 3 # sticky/round/guard bits + (2*mant) - 1
  30         self.product = Signal(mw, reset_less=True)
  31
  32     def eq(self, i):
  33         return [self.z.eq(i.z), self.out_do_z.eq(i.out_do_z), self.oz.eq(i.oz),
  34                 self.product.eq(i.product), self.ctx.eq(i.ctx)]
  35
  36
  37 class FPDivStage0Mod(Elaboratable):
  38
  39     def __init__(self, width, id_wid):
  40         self.width = width
  41         self.id_wid = id_wid
  42         self.i = self.ispec()
  43         self.o = self.ospec()
  44
  45     def ispec(self):
  46         return FPSCData(self.width, self.id_wid, False)
  47
  48     def ospec(self):
  49         return FPDivStage0Data(self.width, self.id_wid)
  50
  51     def process(self, i):
  52         return self.o
  53
  54     def setup(self, m, i):
  55         """ links module to inputs and outputs
  56         """
  57         m.submodules.div0 = self
  58         m.d.comb += self.i.eq(i)
  59
  60     def elaborate(self, platform):
  61         m = Module()
  62
  63         # XXX TODO, actual DIV code here.  this class would be
  64         # "step one" which takes the pre-normalised data (see ispec) and
  65         # *begins* the processing phase (enters the massive DIV
  66         # pipeline chain) - see ospec.
  67
  68         # NOTE: this stage does *NOT* do *ACTUAL* DIV processing,
  69         # it is PURELY the *ENTRY* point into the chain, performing
  70         # "preparation" work
  71
  72         # store intermediate tests (and zero-extended mantissas)
  73         am0 = Signal(len(self.i.a.m)+1, reset_less=True)
  74         bm0 = Signal(len(self.i.b.m)+1, reset_less=True)
  75         m.d.comb += [
  76                      am0.eq(Cat(self.i.a.m, 0)),
  77                      bm0.eq(Cat(self.i.b.m, 0))
  78                     ]
  79         # same-sign (both negative or both positive) div mantissas
  80         with m.If(~self.i.out_do_z):
  81             m.d.comb += [self.o.z.e.eq(self.i.a.e + self.i.b.e + 1),
  82                          # TODO: no, not product, first stage Q and R etc. etc.
  83                          # go here.
  84                          self.o.product.eq(am0 * bm0 * 4),
  85                          self.o.z.s.eq(self.i.a.s ^ self.i.b.s)
  86                 ]
  87
  88         m.d.comb += self.o.oz.eq(self.i.oz)
  89         m.d.comb += self.o.out_do_z.eq(self.i.out_do_z)
  90         m.d.comb += self.o.ctx.eq(self.i.ctx)
  91         return m
  92
  93
  94 class FPDivStage0(FPState):
  95     """ First stage of div.
  96     """
  97
  98     def __init__(self, width, id_wid):
  99         FPState.__init__(self, "divider_0")
 100         self.mod = FPDivStage0Mod(width)
 101         self.o = self.mod.ospec()
 102
 103     def setup(self, m, i):
 104         """ links module to inputs and outputs
 105         """
 106         self.mod.setup(m, i)
 107
 108         # NOTE: these could be done as combinatorial (merge div0+div1)
 109         m.d.sync += self.o.eq(self.mod.o)
 110
 111     def action(self, m):
 112         m.next = "divider_1"