----------------------------------------------------------
-- keyDriver
-- Author   : Gautam Karnik
-- Date     : March 30, 2001
-- Filename : keyDriver.vhd
-- Architecture : Behavioral
-- Description  : This entity drives the output column 
--                lines to the keypad sequentially in order 
--                to determine which key has been pressed.
--                The driver stops driving when the input 
--                lines go back high.
----------------------------------------------------------

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

entity keyDriver is
	      generic ( datawidth : positive := 4 );
	      port ( resetn  	: in std_logic;
			     clock  	: in std_logic;
			     enable 	: in std_logic;
				 keyPressed : in std_logic;
			     driveCol  	: out std_logic_vector(datawidth-1 downto 0);
			     Col  		: out std_logic_vector(datawidth-1 downto 0)
      	        );
end entity keyDriver;

architecture behavioral of keyDriver is 

	signal detecting : std_logic;
	signal high : std_logic;
	signal tmp_Col : std_logic_vector(datawidth-1 downto 0);
	signal tmp_driveCol : std_logic_vector(datawidth-1 downto 0);

begin

	high <= '1';

Key_is_valid : process (clock) is
	begin
		wait until clock'event and clock = '1';
		if (keyPressed = '1' and enable = '0') then
			detecting <= '1';
		elsif (enable = '1') then
			detecting <= '0';
		end if;
	end process Key_is_valid;

drive : process (clock, resetn) is
		variable count : std_logic_vector ( 2 downto 0);
	begin
   		wait until rising_edge ( clock );
   		if ( resetn = '0' ) then
	  		count    := (others => '0');
	  		tmp_driveCol <= (others => '0');
   		else
      		if (detecting = '1' and enable = '0') then
				count := count + '1';	
				CASE count IS
					WHEN "000" =>
						tmp_driveCol <= "0000";
					WHEN "001" =>
						tmp_driveCol <= "0001";
					WHEN "010" =>
						tmp_driveCol <= "0010";
					WHEN "011" => 
						tmp_driveCol <= "0100";
					WHEN "100" =>
						tmp_driveCol <= "1000";
						count := "000";
					WHEN OTHERS =>
						tmp_driveCol<= "0000";
				END CASE;
	  		else
	   			count			:= (others => '0');
				tmp_driveCol	<= "0000";
      		end if;
   		end if;
	end process drive;

-- For the sake of timing relation.
delay_cols_information1 : myflipflops
	generic map (datawidth => 4)
    port map ( 
		clk => clock,
		enable => high,
        clearn => resetn,

        d => tmp_driveCol, 
        q => tmp_Col
    );

register_cols : myflipflops
	generic map (datawidth => 4)
    port map ( 
		clk => clock,
		enable => detecting, -- active high 
        clearn => resetn,   -- active low reset

        d => tmp_Col, 
        q => Col
    );

	driveCol <= tmp_driveCol;

end behavioral;