---------------------------------------------
--Project Gump
--Marc Binette
--Ralph Nevins
--Lambert Lo
----------------------------------------------
--servo_controller_comparator.vhd
--This is a 12 bit comparator that first adds on
--"0001" to the reg_in befor comparing it to
--cnt_in.
--input=>reg_in(8bits), cnt_in(12bits)
--ouput=>compare_out(1bit)

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;

--entity declaration for a comparator that takes
--in two value, where reg_in is four bits shorter
--than cnt_in 
ENTITY servo_controller_comparator IS
	GENERIC(data : positive := 12);
	PORT(reg_in : IN std_logic_vector(data-5 DOWNTO 0);
		cnt_in : IN std_logic_vector(data-1 DOWNTO 0);
		compare_out : BUFFER std_logic);
END servo_controller_comparator;

--behavioural discription of the comparator
ARCHITECTURE behavioural OF servo_controller_comparator IS

--signal used for the reg_in with bit stream "0001" added to 
--the front
SIGNAL extended_reg_in : std_logic_vector(data-1 DOWNTO 0);

BEGIN

--adding "0001" to front of reg_in
extended_reg_in(data-1 DOWNTO data-4) <= "0001";
extended_reg_in(data-5 DOWNTO 0) <= reg_in;

compare : PROCESS IS
BEGIN
--compare_out goes high if cnt_in is smaller than
--reg_in with "0001" added to its front
IF extended_reg_in > cnt_in THEN
	compare_out <= '1';
--otherwise compare_out is low.
ELSE
	compare_out <= '0';
END IF;
END PROCESS compare;
END behavioural;