-- Interactive Audio Manipulation Processor
--
-- file: joystick.vhd
-- status: simulated; works in hardware, but sometimes cursor "teleports"
--
-- author: Stephen Tang
--
-- Uses input from the joystick to update the cursor position

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

library work;
use work.Constants_Pkg.all;

entity joystick is
  port (
    clock : in std_logic;  -- should be the VGA h-sync signal
    up, down, left, right, fire: in std_logic; -- pins TBD
    X: buffer std_logic_vector(DISPLAY_X-1 downto 0);
    Y: buffer std_logic_vector(DISPLAY_Y-1 downto 0)    
  );
end joystick;

architecture driver of joystick is

  constant JOYCOUNT_WIDTH: positive := 6; 
  constant REPEAT_TIME: std_logic_vector(JOYCOUNT_WIDTH-1 downto 0)
    := "101001"; -- 41 ticks 
-- this constant was set to "11" (4-1 ticks)
-- when testing in MAX+plus II simulator

  signal CountTicks: std_logic_vector(JOYCOUNT_WIDTH-1 downto 0);

begin

  UpdatePosition: process (clock)
  begin
    if rising_edge(clock) then
      if CountTicks /= REPEAT_TIME then
      
        CountTicks <= CountTicks + 1;
      
      else  

        -- restart the counter
        CountTicks <= (others => '0');
 
        if (left = '0') and (X /= MIN_X_COORD) then
          X <= X - 1;
        elsif (right = '0') and (X /= MAX_X_COORD) then  
          X <= X + 1;
        end if;
        if (up = '0') and (Y /= MIN_Y_COORD) then
          Y <= Y - 1;
        elsif (down = '0') and (Y /= MAX_Y_COORD) then  
          Y <= Y + 1;
        end if;

      end if;
    end if;    
  end process;

end;