-- Functional Description
--
--  The keypad works with drive and sense lines.  
--  The rows are the sense lines.
--  The columns are the drive lines.
--  Each of the four sense lines is pulled up with a 10kohm 
--  	resister.
--  The drive lines drive all '0' and once a sense of '0' is
--      seen then we know that a key has been pressed.
--  Once the key has been pressed then a '1' bit is shifted through all
--      of the drive lines.  
--  Then once the sense lines goes high again then we know which key
--      was pressed.  
--  The key is then registed using the keydetected signal.
--  Then the kaypad logic waits for the key to be released and for a signal
--      to continue normal operation.      
--
--
--------------------------------------------------------

------------------------------------------------------------------------
--  keypad
------------------------------------------------------------------------
LIBRARY IEEE;
USE ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

ENTITY keypad IS
	PORT(
		clk			: IN	STD_LOGIC;
		reset			: IN	STD_LOGIC;
		--KeyDetected		: OUT 	STD_LOGIC;
		Key			: OUT STD_LOGIC_VECTOR(3 downto 0);

		-- External Signals
		row			: IN STD_LOGIC_VECTOR(3 downto 0);
		col			: OUT STD_LOGIC_VECTOR(3 downto 0)
	     );
END keypad;

ARCHITECTURE behavioural OF keypad IS

	TYPE STATE_TYPE IS (Drive1, Drive2, Drive4, Drive8, Foundkey
			    );
	SIGNAL state      : STATE_TYPE;

--	SIGNAL stateDrive : STATE_TYPE;

	SIGNAL Sense      : STD_LOGIC;

	--SIGNAL Key	  : STD_LOGIC_VECTOR(3 downto 0);
	SIGNAL rowint	  : STD_LOGIC_VECTOR(3 downto 0);
	SIGNAL IntCack	  : STD_LOGIC;
	
BEGIN

	-- Latch the inputs
	Internalrow: PROCESS 
	BEGIN
		IF(falling_edge(clk)) THEN
			rowint <= row;
		END IF;
	END PROCESS Internalrow;

	-- Create the sense signal.
	SenseDetect: PROCESS 
	BEGIN		
		Sense <= (rowint(0) AND rowint(1)) AND (rowint(2) AND rowint(3));
	END PROCESS SenseDetect;

	
-- This is the state that handles all of the state machine.
	StateLogic : PROCESS (reset, clk)
		
	BEGIN

		IF reset = '0' THEN
			--state <= Nokey;
			key <= "0000";
			--keyDetected <= '0';
--			stateDrive <= Drive0;
		ELSIF rising_edge(clk) THEN
			CASE state IS
				
																		
				WHEN Drive1 =>
				IF Sense = '0' THEN
					
					IF 	rowint(0) = '0' THEN
						Key <= "0000"; -- Key 0
					ELSIF rowint(1) = '0' THEN
						Key <= "0100"; --Key 4
					ELSIF rowint(2) = '0' THEN
						Key <= "1000"; -- Key 8
					ELSIF rowint(3) = '0' THEN
						Key <= "1100"; -- Key 12
					end if;
					state <= Foundkey;	
						
				ELSE
					state <= Drive2;				
				END IF;


				WHEN Drive2 =>
				IF Sense = '0' THEN
					if 	rowint(0) = '0' THEN
						Key <= "0001"; -- 1
					ELSIF rowint(1) = '0' THEN
						Key <= "0101"; -- 5
					ELSIF rowint(2) = '0' THEN
						Key <= "1001"; -- 9
					ELSIF rowint(3) = '0' THEN
						Key <= "1101"; -- 13
					end if;
					state <= Foundkey;
				ELSE
					state <= Drive4;				
				END IF;


				WHEN Drive4 =>
				IF Sense = '0' THEN
					if 	rowint(0) = '0' THEN
						Key <= "0010"; -- 2
					ELSIF rowint(1) = '0' THEN
						Key <= "0110"; --6
					ELSIF rowint(2) = '0' THEN
						Key <= "1010"; -- 10
					ELSIF rowint(3) = '0' THEN
						Key <= "1110"; -- 14
					END IF;
					state <= Foundkey;
					
				ELSE
					state <= Drive8;				
				END IF;


				WHEN Drive8 =>
				IF Sense = '0' THEN
					IF 	rowint(0) = '0' THEN
						Key <= "0011"; -- 3
					ELSIF rowint(1) = '0' THEN
						Key <= "0111"; -- 7
					ELSIF rowint(2) = '0' THEN
						Key <= "1011"; -- 11
					ELSIF rowint(3) = '0' THEN
						Key <= "1111"; -- 15
					END IF;
					state <= Foundkey;
						
				ELSE
					--state <= keyrelease;	
					state <= Drive1;			
				END IF;

				
				
				when Foundkey =>
					--state <= debounce_out;
					if sense = '1' then
						--state <= debounce_out;
						--state <= keyrelease;
						state <= Drive1;
					else
						--state <= keyrelease;
						--state <= Nokey;
						state <= Foundkey;
					end if;

				
			END CASE;


			-- Button numbers for the keypad
			-- 0  1  2  3
			-- 4  5  6  7 
			-- 8  9  10 11
			-- 12 13 14 15
		
			-- This case determines what key has been pressed 
			-- based on the drive and the row.
			
		END IF;
	END PROCESS StateLogic;

--------------------------------------------------------
-- Send the key to the output when the Register key state is found
--Outputs: PROCESS(state)
--BEGIN
		--IF(state = Foundkey) THEN
 			--KeyData <= Key;
			--KeyDetected <= '1';
		--ELSE
 			--KeyData <= "0000";
			--keyDetected <= '0';
		--END IF;
--END PROCESS Outputs;


WITH state SELECT
	col 	<=	"0111"	WHEN	Drive1, --7
				"1011"	WHEN	Drive2, --11
				"1101"	WHEN	Drive4, --13
				"1110"	WHEN	Drive8, --14
				--"0000"	WHEN    Drive0,	--15	
				"0000"  when 	others;		
END behavioural;