amaranth/nmigen/compat/genlib/cdc.py

from ...tools import deprecated
from ...lib.cdc import MultiReg
from ...hdl.ast import *
from ..fhdl.module import CompatModule
from ..fhdl.structure import If


__all__ = ["MultiReg", "GrayCounter", "GrayDecoder"]


@deprecated("instead of `migen.genlib.cdc.GrayCounter`, use `nmigen.lib.coding.GrayEncoder`")
class GrayCounter(CompatModule):
    def __init__(self, width):
        self.ce = Signal()
        self.q = Signal(width)
        self.q_next = Signal(width)
        self.q_binary = Signal(width)
        self.q_next_binary = Signal(width)

        ###

        self.comb += [
            If(self.ce,
                self.q_next_binary.eq(self.q_binary + 1)
            ).Else(
                self.q_next_binary.eq(self.q_binary)
            ),
            self.q_next.eq(self.q_next_binary ^ self.q_next_binary[1:])
        ]
        self.sync += [
            self.q_binary.eq(self.q_next_binary),
            self.q.eq(self.q_next)
        ]


@deprecated("instead of `migen.genlib.cdc.GrayDecoder`, use `nmigen.lib.coding.GrayDecoder`")
class GrayDecoder(CompatModule):
    def __init__(self, width):
        self.i = Signal(width)
        self.o = Signal(width, reset_less=True)

        # # #

        o_comb = Signal(width)
        self.comb += o_comb[-1].eq(self.i[-1])
        for i in reversed(range(width-1)):
            self.comb += o_comb[i].eq(o_comb[i+1] ^ self.i[i])
        self.sync += self.o.eq(o_comb)