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daniel.kho |
/*
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This file is part of the Galois Linear Feedback Shift Register
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(galois_lfsr) project:
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http://www.opencores.org/project,galois_lfsr
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Description
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Synthesisable use case for Galois LFSR.
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This example is a CRC generator that uses a Galois LFSR.
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ToDo:
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Author(s):
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- Daniel C.K. Kho, daniel.kho@opencores.org | daniel.kho@tauhop.com
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Copyright (C) 2012-2013 Authors and OPENCORES.ORG
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This source file may be used and distributed without
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restriction provided that this copyright statement is not
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removed from the file and that any derivative work contains
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the original copyright notice and the associated disclaimer.
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This source file is free software; you can redistribute it
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and/or modify it under the terms of the GNU Lesser General
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Public License as published by the Free Software Foundation;
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either version 2.1 of the License, or (at your option) any
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later version.
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This source is distributed in the hope that it will be
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useful, but WITHOUT ANY WARRANTY; without even the implied
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warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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PURPOSE. See the GNU Lesser General Public License for more
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details.
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You should have received a copy of the GNU Lesser General
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Public License along with this source; if not, download it
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from http://www.opencores.org/lgpl.shtml.
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*/
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library ieee; use ieee.std_logic_1164.all, ieee.numeric_std.all; use ieee.math_real.all;
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--use work.types.all;
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entity user is
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generic(
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parallelLoad:boolean:=false;
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tapVector:boolean_vector:=(
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/* Example polynomial from Wikipedia. */
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0|1|2|8=>true, 7 downto 3=>false
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)
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);
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port(
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/* Comment-out for simulation. */
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--clk,reset:in std_ulogic;
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msg:in unsigned(tapVector'length-1 downto 0):=9x"57"; -- Should be (tapVector'length downto 0). TODO report ModelSim bug.
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crc32:out unsigned(31 downto 0):=(others=>'0')
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);
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end entity user;
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architecture rtl of user is
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signal n,c:natural;
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/* Tester signals. */
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signal d:std_ulogic;
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/* synthesis translate_off */
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signal clk,reset:std_ulogic:='0';
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/* synthesis translate_on */
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signal loadEn,computeClk:std_ulogic; -- clock gating.
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signal loaded,i_loaded:boolean;
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signal computed,i_computed:boolean;
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begin
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/* Simulation Tester. */
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/* synthesis translate_off */
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clk<=not clk after 10 ps;
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process is begin
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reset<='0'; wait for 1 ps;
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reset<='1'; wait for 500 ps;
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reset<='0';
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wait;
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end process;
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/* synthesis translate_on */
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loadEn<=clk when reset='0' and not i_computed else '0';
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computeClk<=clk when reset='0' and i_loaded and not i_computed else '0';
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/* CRC computer using LFSR.
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E.g. Design a CRC-32 generator with the following polynomial (CRC-32 algorithm):
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G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10
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+ x^8 + x^7 + x^5 + x^4 + x^2 + x^1 + 1
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Equivalent to the following hex code: 0x04C11DB7, with the MSbit discarded (assumed
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present, but discarded in real implementation to save bits as it does not serve
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any other purpose).
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*/
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i_lfsr: entity work.lfsr(rtl)
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generic map(taps=>tapVector)
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/*generic map(taps => (
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0|1|2|8=>true,
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7 downto 3=>false
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))*/
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port map(nReset=>not reset, clk=>loadEn,
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load=>parallelLoad,
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seed=>msg,
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d=>d,
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q=>crc32(msg'range)
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);
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/* Load message into LFSR. */
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process(reset,loadEn) is begin
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if reset then loaded<=false; n<=msg'length-1; d<='0';
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elsif rising_edge(loadEn) then
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d<='0';
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/* for parallel mode, LFSR automatically loads the seed in parallel. */
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if parallelLoad then d<='0'; loaded<=true;
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else
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if not loaded then d<=msg(n); end if;
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if n>0 then n<=n-1;
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else loaded<=true;
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end if;
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end if;
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end if;
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end process;
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/* Shift zeroes into LFSR after message has been loaded completely. */
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process(reset,loaded,computeClk) is begin
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if reset='1' or not loaded then computed<=false; c<=msg'length-1;
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elsif rising_edge(computeClk) then
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if c>0 then c<=c-1;
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else computed<=true;
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end if;
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end if;
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end process;
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/* Register pipelines. */
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process(clk) is begin
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if falling_edge(clk) then
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i_loaded<=loaded;
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i_computed<=computed;
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end if;
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end process;
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end architecture rtl;
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