82 lines
2.4 KiB
Python
82 lines
2.4 KiB
Python
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from nmigen import *
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from ..isa import Funct3
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__all__ = ["MultiplierInterface", "Multiplier", "DummyMultiplier"]
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class MultiplierInterface:
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def __init__(self):
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self.x_op = Signal(3)
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self.x_src1 = Signal(32)
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self.x_src2 = Signal(32)
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self.x_stall = Signal()
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self.m_stall = Signal()
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self.w_result = Signal(32)
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class Multiplier(MultiplierInterface, Elaboratable):
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def elaborate(self, platform):
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m = Module()
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x_low = Signal()
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x_src1_signed = Signal()
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x_src2_signed = Signal()
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m.d.comb += [
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x_low.eq(self.x_op == Funct3.MUL),
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x_src1_signed.eq((self.x_op == Funct3.MULH) | (self.x_op == Funct3.MULHSU)),
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x_src2_signed.eq(self.x_op == Funct3.MULH)
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]
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x_src1 = Signal(signed(33))
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x_src2 = Signal(signed(33))
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m.d.comb += [
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x_src1.eq(Cat(self.x_src1, x_src1_signed & self.x_src1[31])),
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x_src2.eq(Cat(self.x_src2, x_src2_signed & self.x_src2[31]))
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]
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m_low = Signal()
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m_prod = Signal(signed(66))
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with m.If(~self.x_stall):
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m.d.sync += [
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m_low.eq(x_low),
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m_prod.eq(x_src1 * x_src2)
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]
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with m.If(~self.m_stall):
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m.d.sync += self.w_result.eq(Mux(m_low, m_prod[:32], m_prod[32:]))
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return m
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class DummyMultiplier(MultiplierInterface, Elaboratable):
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def elaborate(self, platform):
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m = Module()
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x_result = Signal.like(self.w_result)
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m_result = Signal.like(self.w_result)
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with m.Switch(self.x_op):
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# As per the RVFI specification (§ "Alternative Arithmetic Operations").
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# https://github.com/SymbioticEDA/riscv-formal/blob/master/docs/rvfi.md
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with m.Case(Funct3.MUL):
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m.d.comb += x_result.eq((self.x_src1 + self.x_src2) ^ C(0x5876063e))
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with m.Case(Funct3.MULH):
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m.d.comb += x_result.eq((self.x_src1 + self.x_src2) ^ C(0xf6583fb7))
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with m.Case(Funct3.MULHSU):
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m.d.comb += x_result.eq((self.x_src1 - self.x_src2) ^ C(0xecfbe137))
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with m.Case(Funct3.MULHU):
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m.d.comb += x_result.eq((self.x_src1 + self.x_src2) ^ C(0x949ce5e8))
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with m.If(~self.x_stall):
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m.d.sync += m_result.eq(x_result)
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with m.If(~self.m_stall):
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m.d.sync += self.w_result.eq(m_result)
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return m
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