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