library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
entity vgacore is
port
(
reset: in std_logic; -- reset
clock: in std_logic; -- VGA dot clock
hsyncb: buffer std_logic; -- horizontal (line) sync
vsyncb: out std_logic; -- vertical (frame) sync
rgb: out std_logic_vector(5 downto 0); -- red,green,blue colors
addr: out std_logic_vector(14 downto 0); -- address to video RAM
data: in std_logic_vector(7 downto 0); -- data from video RAM
csb: out std_logic; -- video RAM chip enable
oeb: out std_logic; -- video RAM output enable
web: out std_logic -- video RAM write enable
);
end vgacore;
architecture vgacore_arch of vgacore is
signal hcnt: std_logic_vector(8 downto 0); -- horizontal pixel counter
signal vcnt: std_logic_vector(9 downto 0); -- vertical line counter
signal pixrg: std_logic_vector(7 downto 0); -- byte register for 4 pixels
signal blank: std_logic; -- video blanking signal
signal pblank: std_logic; -- pipelined video blanking signal


begin

A: process(clock,reset)
begin
-- reset asynchronously clears pixel counter
	if reset='1' then
		hcnt <= "000000000";
-- horiz. pixel counter increments on rising edge of dot clock
	elsif (clock'event and clock='1') then
-- horiz. pixel counter rolls-over after 381 pixels
		if hcnt<380 then
			hcnt <= hcnt + 1;
		else
			hcnt <= "000000000";
		end if;
	end if;
end process;

B: process(hsyncb,reset)
begin
-- reset asynchronously clears line counter
	if reset='1' then
		vcnt <= "0000000000";
-- vert. line counter increments after every horiz. line
	elsif (hsyncb'event and hsyncb='1') then
-- vert. line counter rolls-over after 528 lines
		if vcnt<527 then
			vcnt <= vcnt + 1;
		else
			vcnt <= "0000000000";
		end if;
	end if;
end process;

C: process(clock,reset)
begin
-- reset asynchronously sets horizontal sync to inactive
	if reset='1' then
		hsyncb <= '1';
-- horizontal sync is recomputed on the rising edge of every dot clock
	elsif (clock'event and clock='1') then
-- horiz. sync low in this interval to signal start of new line
		if (hcnt>=291 and hcnt<337) then
			hsyncb <= '0';
		else
			hsyncb <= '1';
		end if;
	end if;
end process;

D: process(hsyncb,reset)
begin
-- reset asynchronously sets vertical sync to inactive
	if reset='1' then
		vsyncb <= '1';
-- vertical sync is recomputed at the end of every line of pixels
	elsif (hsyncb'event and hsyncb='1') then
-- vert. sync low in this interval to signal start of a new frame
		if (vcnt>=490 and vcnt<492) then
			vsyncb <= '0';
		else
			vsyncb <= '1';
		end if;
	end if;
end process;

-- blank video outside of visible region: (0,0) -> (255,479)
E: blank <= '1' when (hcnt>=256 or vcnt>=480) else '0';

-- store the blanking signal for use in the next pipeline stage
F: process(clock,reset)
begin
	if reset='1' then
		pblank <= '0';
	elsif (clock'event and clock='1') then
		pblank <= blank;
	end if;
end process;

-- video RAM control signals
G:
csb <= '0'; -- enable the RAM
web <= '1'; -- disable writing to the RAM
oeb <= blank; -- enable the RAM outputs when video is not blanked

-- read 8 bit data located in addr located in vcnt(x) and hcnt(y)
H: addr <= vcnt(7 downto 0) & hcnt(6 downto 0);

I: process(clock,reset)
begin
-- clear the pixel register on reset
	if reset='1' then
		pixrg <= "00000000";
-- pixel clock controls changes in pixel register
	elsif (clock'event and clock='1') then
		if (vcnt <77) then
			pixrg <= data; -- load 4 pixels from RAM
		else
			pixrg <= "00000000";
		end if;
	end if;
end process;

J: process(clock,reset)
begin
-- blank the video on reset
	if reset='1' then
		rgb <= "000000";
-- update the color outputs on every dot clock
	elsif (clock'event and clock='1') then
-- map the pixel to a color if the video is not blanked
		if pblank='0' then
			case pixrg(7 downto 0) is
-- each pixel represented by 1 byte
				when "00000000" => rgb <= "000000";  -- black
				when "00000001" => rgb <= "000001";  -- dark dark blue
				when "00000010" => rgb <= "000010";  -- navy blue
				when "00000011" => rgb <= "000011";  -- blue 
				when "00000100" => rgb <= "000100";  -- dark green
				when "00000101" => rgb <= "000101";  -- forrest green	
				when "00000110" => rgb <= "000110";  -- blue green tint
				when "00000111" => rgb <= "000111";  -- light blue
				when "00001000" => rgb <= "001000";  -- green
				when "00001001" => rgb <= "001001";  -- green blue
				when "00001010" => rgb <= "001010";  -- sea green
				when "00001011" => rgb <= "001011";  -- sky blue	
				when "00001100" => rgb <= "001100";  -- bright green
				when "00001101" => rgb <= "001101";  -- darker bright green
				when "00001110" => rgb <= "001110";  -- lime green
				when "00001111" => rgb <= "001111";  -- lightest blue
				when "00010000" => rgb <= "010000";  -- dark brown
				when "00010001" => rgb <= "010001";  -- light brown
				when "00010010" => rgb <= "010010";  -- dark purple
				when "00010011" => rgb <= "010011";  -- purple
				when "00010100" => rgb <= "010100";  -- purple blue
				when "00010101" => rgb <= "010101";  -- ugly green
				when "00010110" => rgb <= "010110";  -- dark grey
				when "00010111" => rgb <= "010111";  -- grey blue
				when "00011000" => rgb <= "011000";  -- blue grey
				when "00011001" => rgb <= "011001";  -- light ugly green
				when "00011010" => rgb <= "011010";  -- lighter ugly green
				when "00011011" => rgb <= "011011";  -- bluer ugly green
				when "00011100" => rgb <= "011100";  -- bluer
				when "00011101" => rgb <= "011101";  -- light green
				when "00011110" => rgb <= "011110";  -- lighter green
				when "00011111" => rgb <= "011111";  -- green   
				when "00100000" => rgb <= "100000";  -- light blue
				when "00100001" => rgb <= "100001";  -- brown orange	
				when "00100010" => rgb <= "100010";  -- brown purple
				when "00100011" => rgb <= "100011";  
				when "00100100" => rgb <= "100100";
				when "00100101" => rgb <= "100101";
				when "00100110" => rgb <= "100110";
				when "00100111" => rgb <= "100111";
				when "00101000" => rgb <= "101000";
				when "00101001" => rgb <= "101001";
				when "00101010" => rgb <= "101010";
				when "00101011" => rgb <= "101011";
				when "00101100" => rgb <= "101100";
				when "00101101" => rgb <= "101101";
				when "00101110" => rgb <= "101110";
				when "00101111" => rgb <= "101111";
				when "00110000" => rgb <= "110000";
				when "00110001" => rgb <= "110001";
				when "00110010" => rgb <= "110010";
				when "00110011" => rgb <= "110011";
				when "00110100" => rgb <= "110100";
				when "00110101" => rgb <= "110101";
				when "00110110" => rgb <= "110110";
				when "00110111" => rgb <= "110111";
				when "00111000" => rgb <= "111000";
				when "00111001" => rgb <= "111001";
				when "00111010" => rgb <= "111010";
				when "00111011" => rgb <= "111011";
				when "00111100" => rgb <= "111100";  -- yellow
				when "00111101" => rgb <= "111101";  -- yellow
				when "00111110" => rgb <= "111110";  -- yellow
				when "11111111" => rgb <= "111111";
				when others => rgb <= "111111"; -- white
			end case;	
-- otherwise, output black if the video is blanked
		else
			rgb <= "000000"; -- black
		end if;
	end if;
end process;
end vgacore_arch;