myhdl/example/arith_lib/Dec.py

import myhdl
from myhdl import *
from arith_utils import BEHAVIOR
from PrefixAnd import PrefixAnd


def Dec(width, speed, A, Z, architecture=BEHAVIOR):

    """ Decrementer module.

    width -- bitwidth of input and output
    speed -- SLOW, MEDIUM, or FAST performance
    A -- input
    Z -- output
    architecture -- BEHAVIOR or STRUCTURE architecture selection

    """

    @instance
    def Behavioral():
        while 1:
            yield A
            Z.next = A - 1

    def Structural():
        AI = Signal(intbv(0))
        PO = Signal(intbv(0))
        prefix = PrefixAnd(width, speed, AI, PO)

        @instance
        def comb():
            while 1:
                yield A, PO
                AI.next = ~A
                Z.next = A ^ concat(PO[width - 1:], '1')

        return [prefix, comb]

    if architecture == BEHAVIOR:
        return Behavioral
    else:
        return Structural()