-- PROJECT: D0 Run IIb Trigger L1 Calorimeter upgrade
--
-- MODULE: Channel Link Receiver Test Card
--
-- ELEMENT: trigger
--
-- DESCRIPTION: trigger generator
-- Activates a trigger output when the input pattern
-- matches the trigger pattern. Each bit can match on 0,
-- 1 or can be masked so that it does not participate to
-- the trigger. If mask is 0, all bits participate in
-- the trigger. Input FORCE is used to set the output
-- independentely of all other inputs 
--
-- AUTHOR: D. Calvet calvet@hep.saclay.cea.fr
--
-- DATE AND HISTORY:
--  June 2003 : created
--
--
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.all;
--------------------------------------------------------------------------------

--
-- Trigger
--
ENTITY trigger is
	generic (
		SIZE : NATURAL := 8
	);
	port (
		-----------------------------------------------------------------------
		RESET            : in std_logic; -- Reset
		CLK              : in std_logic; -- Clock
		-----------------------------------------------------------------------

		-----------------------------------------------------------------------
		--
		-- Inputs
		--
		DATA           : in std_logic_vector((SIZE-1) downto 0); -- Data
		MATCH          : in std_logic_vector((SIZE-1) downto 0); -- Match
		MASK           : in std_logic_vector((SIZE-1) downto 0); -- Mask
		FORCE          : in std_logic; -- To force a match
		-----------------------------------------------------------------------
		
		-----------------------------------------------------------------------
		--
		-- Output
		--
		TRIG           : out std_logic -- Indicates a match
		-----------------------------------------------------------------------
	);
END trigger;

architecture structure of trigger is

begin
	
	-- MatchPattern : process(DATA, MATCH, MASK, FORCE)
	MatchPattern : process(RESET, CLK)
	variable trig_int : std_logic;
	begin
		if RESET = '1' then
			TRIG <= '0';
		elsif CLK'event and CLK = '1' then
			for i IN SIZE downto 0 loop
				if i = SIZE then
					trig_int := '1'; -- assume pattern matches
				else
					-- as soon as a bit is non masked and does not match: clear trig_int
					if MASK(i) = '0' and (DATA(i) /= MATCH(i)) then
						trig_int := '0';
					end if;
				end if;
			end loop;
			TRIG <= trig_int or FORCE;
		end if;
	end process;	
end;