lfsr.vhd

台湾全华科技VHDL教材实例

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_signed.all;
use std.textio.all;

entity LFSR is
	generic(BitNumber : integer := 32);
	port(OutNumberA : out std_logic_vector(BitNumber - 1 downto 0);
	     OutNumberB : out std_logic_vector(BitNumber - 1 downto 0);
	     Seed 		: in  std_logic_vector(BitNumber downto 0);
		 Reset		: in  std_logic;
		 Clk   		: in  std_logic);
end LFSR;

architecture behav of LFSR is

	signal x 	: std_logic_vector(BitNumber downto 0);
	signal y 	: std_logic_vector(BitNumber downto 0);
	signal cNum : std_logic_vector(BitNumber - 1 downto 1);
	signal bNum : integer;
	
begin

	bNum <= BitNumber;
	
	process
		file DA : text open write_mode is "DataB.dat"; 
		variable DLine : line;
		variable px : std_logic_vector(BitNumber downto 1);
		variable py : std_logic_vector(BitNumber downto 1);
	begin
		wait until Clk = '1' and Clk'event;
			if Reset = '0' then
				x <= Seed;
				y <= Seed + 1;
			else
				for i in BitNumber - 1 downto 1 loop
					px(BitNumber) := x(BitNumber);
					px(i) := (x(i) and cNum(i)) xor px(i + 1);
					x(0) <= px(1); 
					x(i) <= x(i - 1);	
					x(BitNumber) <= x(BitNumber - 1);			
				end loop;
				for i in BitNumber - 1 downto 1 loop
					py(BitNumber) := y(BitNumber);
					py(i) := (x(i) and cNum(i)) xor py(i + 1);
					y(0) <= py(1); 
					y(i) <= y(i - 1);	
					y(BitNumber) <= y(BitNumber - 1);			
				end loop;
				OutNumberA <= x(BitNumber downto 1);
				OutNumberB <= y(BitNumber downto 1);
				write(DLine,CONV_INTEGER(x(BitNumber downto 1)),right,15);
				write(DLine,CONV_INTEGER(y(BitNumber downto 1)),right,15);
				writeline(DA,DLine);
			end if;
	end process;
	process(bNum)
	begin
		case bNum is
			when 3 =>
				cNum <= "10";
			when 4 =>
				cNum <= "100";
			when 5 =>
				cNum <= "1000";
			when 6 =>
				cNum <= "01000";
			when 7 =>
				cNum <= "100000";
			when 8 =>
				cNum <= "1000000";
			when 9 =>
				cNum <= "10001100";
			when 10 =>
				cNum <= "000100000";
			when 11 =>
				cNum <= "0010000000";
			when 12 =>
				cNum <= "01000000000";
			when 13 =>
				cNum <= "001100100000";
			when 14 =>
				cNum <= "0110000000001";
			when 15 =>
				cNum <= "00000000000001";
			when 16 =>
				cNum <= "000000000010110";
			when 17 =>
				cNum <= "0000000000000100";
			when 18 =>
				cNum <= "00000000001000000";
			when 19 =>
				cNum <= "000000000000110001";
			when 20 =>
				cNum <= "0000000000000000100";
			when 21 =>
				cNum <= "00000000000000000010";
			when 22 =>
				cNum <= "000000000000000000001";
			when 23 =>
				cNum <= "0000000000000000010000";
			when 24 =>
				cNum <= "00000000000000000001101";
			when 25 =>
				cNum <= "000000000000000000000100";
			when 26 =>
				cNum <= "0000000000000000011000001";
			when 27 =>
				cNum <= "00000000000000000011000001";
			when 28 =>
				cNum <= "000000000000000000000000100";
			when 29 =>
				cNum <= "0000000000000000000000000010";
			when 30 =>
				cNum <= "00000000000001100000000000001";
			when 31 =>
				cNum <= "000000000000000000000000000100";
			when 32 =>
				cNum <= "0001100000000000000000000000001";
			when 33 =>
				cNum <= "00000000000000000001000000000000";
			when 34 =>
				cNum <= "000000000000000000110000000000001";
			when 35 =>
				cNum <= "0000000000000000000000000000000010";
			when 36 =>
				cNum <= "00000000000000000000000010000000000";
			when others =>
		end case;
	end process;
		
end behav;