잡다한 인생

--
--	VHDL을 이용한 FPGA 설계
--	3장. section07. n비트 가산 / 감산기
--		DE2-117 구현
--
library ieee;
use ieee.std_logic_1164.all;

package my_package is

	constant	adder_width		:	integer := 4;
	constant	result_width	:	integer := 5;
	constant	max_result		:	integer := 2**result_width - 1;
	constant	min_result		:	integer := -2**result_width;
	
	subtype		adder_value		is	integer range 0 to 2**adder_width - 1;
	subtype		result_value	is	integer range min_result to max_result;
	
end my_package;


library ieee;
use ieee.std_logic_1164.all;
use work.my_package.all;

entity nbitAddSub is

	port (
		a, b		:	in		adder_value;
		mode		:	in		std_logic;
		sega		:	out		std_logic_vector (6 downto 0);	-- hex6 of de2-117
		segb		:	out		std_logic_vector (6 downto 0);	-- hex4 of de2-117
		segmode		:	out		std_logic_vector (6 downto 0);	-- hex3 of de2-117
		segsign		:	out		std_logic;						-- hex2 of de2-117
		seg1		:	out		std_logic_vector (6 downto 0);	-- hex0 of de2-117
		seg2		:	out		std_logic_vector (6 downto 0);	-- hex1 of de2-117
		underflow	:	out		std_logic;
		overflow	:	out		std_logic
	);
	
end nbitAddSub;


architecture arc of nbitAddSub is

	signal	over, under	:	std_logic;
	signal	seg1Reg, seg2Reg	:	integer range 0 to 15;


	-- convert integer value to drive 7-segment
	--
	function toSeg(
		in_value	:	in	integer range 0 to 15
	) return std_logic_vector is
	begin
	
		case in_value is
		
			when 0	 	=>	return "1000000";
			when 1		=>	return "1111001";
			when 2		=>	return "0100100";
			when 3		=>	return "0110000";
			when 4		=>	return "0011001";
			when 5		=>	return "0010010";
			when 6		=>	return "0000010";
			when 7		=>	return "1011000";
			when 8		=>	return "0000000";
			when 9		=>	return "0011000";
			when 10		=>	return "0001000";
			when 11		=>	return "0000011";
			when 12		=>	return "0100111";
			when 13		=>	return "0100001";
			when 14		=>	return "0000110";
			when 15		=>	return "0001110";
			when others	=>	return "1111111";

		end case;
			
	end toSeg;

begin


	process (mode, a, b, over, under)
		variable res	:	result_value;
	begin

		if (mode = '1') then		-- if key0 is not pressed
			res		:=	a + b;
			segmode	<=	toSeg(10);	-- display 'A' for mode add
		else
			res		:=	a - b;
			segmode	<=	toSeg(5);	--	display 'S' for mode subtraction
		end if;

	
		if (res > max_result) then
			over	<=	'1';
		else
			over	<=	'0';
		end if;


		if (res < min_result) then
			under	<=	'1';
		else
			under	<=	'0';
		end if;


		if (res < 0) then
			segsign	<=	'0';		-- turn on minus sign
			seg2Reg	<=	-res / 16;
			seg1Reg	<=	-res mod 16;
		else
			segsign	<=	'1';		-- turn off minus sign
			seg2Reg	<=	res / 16;
			seg1Reg	<=	res mod 16;
		end if;

		overflow	<=	over;
		underflow	<=	under;

	end process;


	sega	<=	toSeg(a);
	segb	<=	toSeg(b);
	seg1	<=	toSeg(seg1Reg);
	seg2	<=	toSeg(seg2Reg);

	
end arc;