riscv-formal-nmigen/rvfi/cores/minerva/units/shifter.py

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from nmigen import *
__all__ = ["Shifter"]
class Shifter(Elaboratable):
def __init__(self):
self.x_direction = Signal()
self.x_sext = Signal()
self.x_shamt = Signal(5)
self.x_src1 = Signal(32)
self.x_stall = Signal()
self.m_result = Signal(32)
def elaborate(self, platform):
m = Module()
x_operand = Signal(32)
x_filler = Signal()
m_direction = Signal()
m_result = Signal(32)
m.d.comb += [
# left shifts are equivalent to right shifts with reversed bits
x_operand.eq(Mux(self.x_direction, self.x_src1, self.x_src1[::-1])),
x_filler.eq(Mux(self.x_direction & self.x_sext, self.x_src1[-1], 0))
]
with m.If(~self.x_stall):
m.d.sync += [
m_direction.eq(self.x_direction),
m_result.eq(Cat(x_operand, Repl(x_filler, 32)) >> self.x_shamt)
]
m.d.comb += self.m_result.eq(Mux(m_direction, m_result, m_result[::-1]))
return m