-------------------------------------------------------------------------------
-- File: input_synchronizer.vhd
--		Taken from the traffic light controller from Feng Gui, Taozhi Peng
--		Khern Yang Tkwang(Keypad Application Note) 1999_w 
--		and modified different valid requirements
--
--
-- Project: DPF
-- Created by: Benjamin Talbot from Feng Gui, Taozhi Peng
--				Khern Yang Tkwang(Keypad Application Note) 1999_w
-- Date: 2/1/02
--
-- Purpose: To synchronize a asynchronous input to the system clock
--
-- Inputs:      button_in      	<- PushButton 
--              syn_clock       <- System clock to synchronize to
--              syn_reset       <- reset for synchronizer
--
-- Outputs:     syn_button_out  -> synchronized button signal
--
-- External Connections:
--      keypad_controller.vhd
-------------------------------------------------------------------------------
library ieee;
use ieee.std_logic_1164.all;

entity button_input_synchronizer1 is
	-- latch short pulses on button presses , and synchronize to the clock
	-- clear automatically after one clock or on a reset
	port( 
			button_in : in std_logic;	-- negative logic input button 
			syn_clock : in std_logic;-- system clock to synchronize
			reset	: in std_logic;
			syn_button_out : out std_logic
    	);
end button_input_synchronizer1;

architecture behavioural of button_input_synchronizer1 is

component clkdiv IS
   -- default to .75H
   -- 25.175 MHz/ (2**24) /2
   generic (Divisor: positive :=33554432); -- clock division rate
   port(fast_clock : in STD_LOGIC;
        reset      : in STD_LOGIC;
        slow_clock : buffer STD_LOGIC);
end component clkdiv;


SIGNAL SHIFT_PB : STD_LOGIC_VECTOR(3 DOWNTO 0);
signal pb_debounced : std_logic;
signal check_clock : std_logic;

begin

	slow_clock : clkdiv
		generic map(Divisor => 50)
		port map( fast_clock => syn_clock,
			  		reset => reset,
			  		slow_clock => check_clock);	

	-- Debounce clock should be approximately 10ms or 100Hz
    debounce : process(check_clock)
    BEGIN
        if rising_edge(check_clock) then
	      -- Use a shift register to filter switch contact bounce
	        SHIFT_PB(2 DOWNTO 0) <= SHIFT_PB(3 DOWNTO 1);
	        SHIFT_PB(3) <=  not button_in;
	       	IF SHIFT_PB(3 DOWNTO 0)="0000" THEN
	 			pb_debounced <= '0';
	 		ELSE 
	 			pb_debounced <= '1';
	   		END IF;
		end if;
   	END PROCESS;

	syn_button_out <= pb_debounced;
	
end behavioural;