headers_beh.vhd

vhdl code for GIF Image Viewer

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity headers_beh is
    Port (
		clk : in std_logic;
	 	rstL : in std_logic;
		start : in std_logic;
		paletteProgDone : in std_logic;
 	 	readData : in std_logic_vector(15 downto 0);
		addr : out std_logic_vector(19 downto 0);
		writeData : out std_logic_vector(15 downto 0);
		oen : out std_logic;
		wen : out std_logic;
		height : out std_logic_vector(9 downto 0);
		width : out std_logic_vector(9 downto 0);
		codesize : out std_logic_vector(3 downto 0);
		coltablecode : out std_logic_vector(2 downto 0);
		startPaletteProg : out std_logic;
		done : out std_logic
	);
end headers_beh;

architecture Behavioral of headers_beh is

begin

	process
		variable inaddr, outaddr : std_logic_vector(19 downto 0);
		variable data, blksize : std_logic_vector(7 downto 0);
	begin
		oen <= '0';
		wen <= '1';
		startPaletteProg <= '0';
		done <= '0';
		writeData <= x"0000";

		wait until start = '1';

		inaddr := x"8000a";
		outaddr := x"00000";

		addr <= inaddr;
		wait for 20 ns;
		data := readData(7 downto 0);

		inaddr := inaddr + 3;

		if data(7) = '1' then
			coltablecode <= data(2 downto 0);
			startPaletteProg <= '1';
			wait for 20 ns;
			startPaletteProg <= '0';
			wait until paletteProgDone = '1';

			inaddr := inaddr + SHL("0000000001", data(2 downto 0) + 1);
			inaddr := inaddr + SHL("0000000001", data(2 downto 0) + 1);
			inaddr := inaddr + SHL("0000000001", data(2 downto 0) + 1);
		end if;

		outer : loop
			addr <= inaddr;
			wait for 20 ns;
			data := readData(7 downto 0);

			if data = x"21" then
				inaddr := inaddr + 2;
				inner : loop
					addr <= inaddr;
					wait for 20 ns;
					data := readData(7 downto 0);
					if data = x"00" then
						exit inner;
					end if;
					inaddr := inaddr + data + 1;
				end loop;

				inaddr := inaddr + 1;
			else
				exit outer;
			end if;
		end loop;

		inaddr := inaddr + 5;

		addr <= inaddr;
		wait for 20 ns;
		width(7 downto 0) <= readData(7 downto 0);
		inaddr := inaddr + 1;

		addr <= inaddr;
		wait for 20 ns;
		width(9 downto 8) <= readData(1 downto 0);
		inaddr := inaddr + 1;

		addr <= inaddr;
		wait for 20 ns;
		height(7 downto 0) <= readData(7 downto 0);
		inaddr := inaddr + 1;

		addr <= inaddr;
		wait for 20 ns;
		height(9 downto 8) <= readData(1 downto 0);
		inaddr := inaddr + 1;

		addr <= inaddr;
		wait for 20 ns;
		data := readData(7 downto 0);
		inaddr := inaddr + 1;

		if data(7) = '1' then
			coltablecode <= data(2 downto 0);
			startPaletteProg <= '1';
			wait for 20 ns;
			startPaletteProg <= '0';
			wait until paletteProgDone = '1';
			inaddr := inaddr + SHL("0000000001", data(2 downto 0) + 1);
			inaddr := inaddr + SHL("0000000001", data(2 downto 0) + 1);
			inaddr := inaddr + SHL("0000000001", data(2 downto 0) + 1);
		end if;

		addr <= inaddr;
		wait for 20 ns;
		codesize <= readData(3 downto 0);
		inaddr := inaddr + 1;

		image : loop
			addr <= inaddr;
			wait for 20 ns;
			blksize := readData(7 downto 0);
			inaddr := inaddr + 1;

			if blksize = x"00" then
				exit image;
			end if;

			subblock : loop
				addr <= inaddr;
				wait for 20 ns;
				data := readData(7 downto 0);
				inaddr := inaddr + 1;

				writeData <= x"00" & data;
				addr <= outaddr;
				wen <= '0';
				wait for 20 ns;
				wen <= '1';
				wait for 20 ns;

				outaddr := outaddr + 1;
				blksize := blksize - 1;
				if blksize = x"00" then
					exit subblock;
				end if;
			end loop;

			inaddr := inaddr + 1;
		end loop;

		done <= '1';
		wait for 20 ns;
		done <= '0';
	end process;


end Behavioral;