-- parking garage. 
-- Two sensors count cars entering and leaving the parking garage.
-- INpb counts the cars entering. OUTpb counts the cars leaving. 
-- Each sensor is debounced.
-- LotFull simulates a closing gate blocking cars from entering the lot once it is full.
-- The lot is full when the car count is 9.
-- clk is the UP-1 oscillator input.  q is the car counter. 

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;

ENTITY park IS
	PORT(       
        INpb, OUTpb, clk 	: IN	STD_LOGIC;
        q					: OUT   INTEGER RANGE 0 TO 15;
     	LotFull				: OUT	STD_LOGIC);
END park;

ARCHITECTURE a OF park IS
	SIGNAL SHIFT4in 		: STD_LOGIC_VECTOR(3 DOWNTO 0);
	SIGNAL SHIFT4out 		: STD_LOGIC_VECTOR(3 DOWNTO 0);
	BEGIN
	PROCESS (clk, INpb, OUTpb)
	    VARIABLE    debcnt    	: INTEGER RANGE 0 TO 131071; -- approx. 5 millisecond interval for debounce
	    VARIABLE    cnt     	: INTEGER RANGE 0 TO 15;	 -- car counter
		Variable 	debup, debdown		: INTEGER RANGE 0 TO 1; -- used as a flag bit.
		BEGIN
			IF (clk'EVENT AND clk = '1') THEN
				debcnt := debcnt + 1;
				-- Car entering garage (INpb is the car entering pushbutton)
				IF (debcnt = 131071) THEN
					SHIFT4in(3 DOWNTO 1) <= SHIFT4in(2 DOWNTO 0);
		  			SHIFT4in(0) <= INpb;
					END IF;
	  			IF SHIFT4in(3 DOWNTO 0)="1111" THEN
	   				if (debup = 1) then cnt := cnt +1;  debup := 0; end if; --count a car and reset debup flag when PB is released (1).
					else
					debup := 1;  -- set debup flag while PB is being held down (0). 
					End if;
				-- Car leaving garage (OUTpb is the car leaving pushbutton)
				IF (debcnt = 131071) THEN
					SHIFT4out(3 DOWNTO 1) <= SHIFT4out(2 DOWNTO 0);
		  			SHIFT4out(0) <= OUTpb;
					END IF;
	  			IF SHIFT4out(3 DOWNTO 0)="1111" THEN
   	   				if (debdown = 1) then cnt := cnt -1; debdown := 0; end if; -- remove a car and reset debdown flag when PB is released (1).
					else
					debdown := 1; -- set debdown flag while PB is being held down (0).
					End if;
	
  				if (cnt =10) then cnt := 9; END IF; 
				if (cnt =15) then cnt := 0; END IF; 
  				if (cnt =9) then LotFull <= '1'; else Lotfull <= '0'; END IF; 
				END IF;
		q	<=	cnt;

		END PROCESS;
	END a;