Subversion Repositories myhdl_lfsr

from myhdl import *

from lfsr_tap_table import *

import random

#Author: Shawn Rainey 

#        rainey.shawn@gmail.com

#init_value must not be 0

def get_lfsr(width=32, init_value=1):

    if init_value == 0:

        raise SystemExit("LFSR May not be instantiated with initial zero value")

    tap_const = intbv(0)[width:]

    for i in lfsr_tap_table[width]:

        tap_const[i-1] = 1

    def lfsr_module(reset, clock, lfsr_out):

        reg_internal = Signal(intbv(init_value)[width:])

        @always_comb

        def assign_out():

            lfsr_out.next = reg_internal

        @always_seq(clock.posedge, reset=reset)

        def lfsr_logic():

            if reg_internal[0] == 1:

                #use of _val here may not be forward or backward compatible

                #with other versions of MyHDL

                #works with MyHDL 0.9.0

                reg_internal.next = (reg_internal >> 1) ^ tap_const._val

            else:

                reg_internal.next = reg_internal >> 1

        return instances()

    return lfsr_module