----------------------------------------------------------------------------------
-- Company: FMAC
-- Engineer: Craig and Naveen
-- 
-- Create Date:    17:17:28 12/23/2008 
-- Design Name: Brainless uProcessor 
-- Module Name:    sw_Buffer - Behavioral 
-- Description: 
-- This buffer is designed to debounce the Spartan 3E buttons.
-- Without a buffer the buttons will "bounce" when pressed. This will send
-- 2 maybe 3 high signals each time the button is pressed. Using a counter
-- that is triggered off the Spartan 3E's 50MHz oscillator, each time the
-- button is pressed a delay of 0.23 seconds is introduced to allow the
-- signal to stop "bouncing".
--
----------------------------------------------------------------------------------

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

entity debounce is
port	(
		clk					:	in	std_logic;
		switch_input		:	in	std_logic;
		debounced_output	:	out	std_logic := '0'
		);
end debounce ;

architecture behavioral of debounce is

type states is (noPushButton, ButtonPushed);
signal state   : states;
signal stop_counter  : std_logic := '0';
signal run_counter   :std_logic;
signal counter :std_logic_vector(23 downto 0);


begin

state_machine: process (clk)
begin
	if clk'event and clk='1' then
			case state is 
				when noPushButton =>
									if (switch_input = '1' and stop_counter = '0') then
										state <= ButtonPushed;
										debounced_output <= '0';
										run_counter <= '1';
									else
										state <= noPushButton;
										debounced_output <= '0';
										run_counter <= '0';
									end if;
												
				when ButtonPushed =>
									if stop_counter = '1' then
										state <= noPushButton;
										debounced_output <= '1';
										run_counter <= '0';
									else
										state <= ButtonPushed;
										debounced_output <= '0';
										run_counter <= '1';
									end if;	    
					
				when others =>
									debounced_output <= '0';
									run_counter <= '0';
									state <= noPushButton;
				end case;
	end if;						
	
end process state_machine;

-- When the state machine goes 'high', it starts the counter (run_counter = 1).
-- The counter will count off from 0 to 11,500,000. When it is
-- done it will give stop_counter a '1', which will output 1 and change
-- state to 'low'.
count_machine: process(clk, run_counter)
begin
		if run_counter = '1'	then
			if clk'event and clk = '1' then
					if counter = x"AF79E0" then--x"AF79E0" then	-- this hex value is 11,500,000
						stop_counter <= '1';			--	each cycle is 20 ns
					else 									-- total time of counter is
						stop_counter <= '0';			-- 11,500,000 * 20 ns = 0.23 sec
					end if;
					counter <= counter + 1;
			end if;
		else 
			counter <= x"000000";
		end if;
	end process count_machine;



end behavioral;