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sonicwave |
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-- Company: University of Southern Denmark
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-- Engineer: Simon Falsig
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--
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-- Create Date: 9/6/2008
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-- Design Name: Linear Feedback Shift Register
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-- Module Name: lfsr - Behavioral
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-- File Name: lfsr.vhd
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-- Project Name: TosNet
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-- Target Devices: Spartan3/6
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-- Tool versions: Xilinx ISE 12.2
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-- Description: The LFSR is used to create pseudo-random sequences that are
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-- used for scrambling outgoing data. With a similarly seeded
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-- LFSR on the receiving side, the data can be de-scrambled.
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--
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-- Revision:
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-- Revision 3.2 - Initial release
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--
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-- Copyright 2010
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--
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-- This module is free software: you can redistribute it and/or modify
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-- it under the terms of the GNU Lesser General Public License as published by
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-- the Free Software Foundation, either version 3 of the License, or
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-- (at your option) any later version.
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--
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-- This module is distributed in the hope that it will be useful,
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-- but WITHOUT ANY WARRANTY; without even the implied warranty of
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-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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-- GNU Lesser General Public License for more details.
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--
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-- You should have received a copy of the GNU Lesser General Public License
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-- along with this module. If not, see <http://www.gnu.org/licenses/>.
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----------------------------------------------------------------------------------
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library IEEE;
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use IEEE.STD_LOGIC_1164.ALL;
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use IEEE.STD_LOGIC_ARITH.ALL;
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use IEEE.STD_LOGIC_UNSIGNED.ALL;
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use IEEE.NUMERIC_STD.ALL;
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entity lfsr is
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generic (
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lfsr_length : STD_LOGIC_VECTOR(7 downto 0);
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lfsr_out_length : STD_LOGIC_VECTOR(7 downto 0);
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lfsr_allow_zero : STD_LOGIC);
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port (
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lfsr_out : out STD_LOGIC_VECTOR((conv_integer(lfsr_out_length) - 1) downto 0);
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lfsr_seed : in STD_LOGIC_VECTOR((conv_integer(lfsr_length) - 1) downto 0);
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lfsr_reset : in STD_LOGIC;
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lfsr_clk : in STD_LOGIC;
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lfsr_clk_en : in STD_LOGIC);
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end lfsr;
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architecture Behavioral of lfsr is
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signal value : STD_LOGIC_VECTOR((conv_integer(lfsr_length) - 1) downto 0);
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begin
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process(lfsr_clk)
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begin
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if(lfsr_clk = '1' and lfsr_clk'EVENT) then
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if(lfsr_reset = '1') then
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value <= lfsr_seed;
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lfsr_out <= (others => '0');
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elsif(lfsr_clk_en = '1') then
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value((conv_integer(lfsr_length) - 2) downto 0) <= value((conv_integer(lfsr_length) - 1) downto 1);
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value((conv_integer(lfsr_length) - 1)) <= value(1) xor value(0);
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if(lfsr_allow_zero = '0' and value((conv_integer(lfsr_length) - 1) downto (conv_integer(lfsr_length) - conv_integer(lfsr_out_length))) = 0) then
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lfsr_out <= (others => '1');
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else
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lfsr_out <= value((conv_integer(lfsr_length) - 1) downto (conv_integer(lfsr_length) - conv_integer(lfsr_out_length)));
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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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end Behavioral;
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