src/soc/minerva/units/multiplier.py

   1 from nmigen import *
   2
   3 from ..isa import Funct3
   4
   5
   6 __all__ = ["MultiplierInterface", "Multiplier", "DummyMultiplier"]
   7
   8
   9 class MultiplierInterface:
  10     def __init__(self):
  11         self.x_op     = Signal(3)
  12         self.x_src1   = Signal(32)
  13         self.x_src2   = Signal(32)
  14         self.x_stall  = Signal()
  15         self.m_stall  = Signal()
  16
  17         self.w_result = Signal(32)
  18
  19
  20 class Multiplier(MultiplierInterface, Elaboratable):
  21     def elaborate(self, platform):
  22         m = Module()
  23
  24         x_low = Signal()
  25         x_src1_signed = Signal()
  26         x_src2_signed = Signal()
  27
  28         m.d.comb += [
  29             x_low.eq(self.x_op == Funct3.MUL),
  30             x_src1_signed.eq((self.x_op == Funct3.MULH) | (self.x_op == Funct3.MULHSU)),
  31             x_src2_signed.eq(self.x_op == Funct3.MULH)
  32         ]
  33
  34         x_src1 = Signal(signed(33))
  35         x_src2 = Signal(signed(33))
  36
  37         m.d.comb += [
  38             x_src1.eq(Cat(self.x_src1, x_src1_signed & self.x_src1[31])),
  39             x_src2.eq(Cat(self.x_src2, x_src2_signed & self.x_src2[31]))
  40         ]
  41
  42         m_low = Signal()
  43         m_prod = Signal(signed(66))
  44
  45         with m.If(~self.x_stall):
  46             m.d.sync += [
  47                 m_low.eq(x_low),
  48                 m_prod.eq(x_src1 * x_src2)
  49             ]
  50
  51         with m.If(~self.m_stall):
  52             m.d.sync += self.w_result.eq(Mux(m_low, m_prod[:32], m_prod[32:]))
  53
  54         return m
  55
  56
  57 class DummyMultiplier(MultiplierInterface, Elaboratable):
  58     def elaborate(self, platform):
  59         m = Module()
  60
  61         x_result = Signal.like(self.w_result)
  62         m_result = Signal.like(self.w_result)
  63
  64         with m.Switch(self.x_op):
  65             # As per the RVFI specification (§ "Alternative Arithmetic Operations").
  66             # https://github.com/SymbioticEDA/riscv-formal/blob/master/docs/rvfi.md
  67             with m.Case(Funct3.MUL):
  68                 m.d.comb += x_result.eq((self.x_src1 + self.x_src2) ^ C(0x5876063e))
  69             with m.Case(Funct3.MULH):
  70                 m.d.comb += x_result.eq((self.x_src1 + self.x_src2) ^ C(0xf6583fb7))
  71             with m.Case(Funct3.MULHSU):
  72                 m.d.comb += x_result.eq((self.x_src1 - self.x_src2) ^ C(0xecfbe137))
  73             with m.Case(Funct3.MULHU):
  74                 m.d.comb += x_result.eq((self.x_src1 + self.x_src2) ^ C(0x949ce5e8))
  75
  76         with m.If(~self.x_stall):
  77             m.d.sync += m_result.eq(x_result)
  78         with m.If(~self.m_stall):
  79             m.d.sync += self.w_result.eq(m_result)
  80
  81         return m