CPLD LED Fading

The Software
           The VHDL module we'll write to fade LEDs is surprisingly and thankfully simple. It's a combo of our log table and a few counters, thus the code is split into two main parts:
    -Logrithmic Value Table
    -PWM Generation Counters

           The table of values is hardcoded in a ROM inside the VHDL. Then when a value is needed the PWM counters insert an address into the ROM and the ROM spits out the correlating logarithmic value.

VHDL ROM

type nums is array(0 to 31) of integer;
constant my_nums : nums := (
	0	=>		0,
	1	=>		2,
	2	=>		4,
	3	=>		6,
	4	=>		8,
	5	=>		10,
	6	=>		12,
	7	=>		15,
	8	=>		18,
	9	=>		21,
	10	=>		24,
	11	=>		28,
	12	=>		31,
	13	=>		34,
	14	=>		38,
	15	=>		42,
	16	=>		46,
	17	=>		51,
	18	=>		56,
	19	=>		61,
	20	=>		66,
	21	=>		72,
	22	=>		85,
	23	=>		93,
	24	=>		102,
	25	=>		112,
	26	=>		123,
	27	=>		137,
	28	=>		153,
	29	=>		174,
	30	=>		204,
	31	=>		255
);		

           The Main PWM generation code uses some counters and a constant period of 256 clock cycles. A seperate counter constantly counts up to 31 and back to 0, this is what tells the ROM which 0-255 value to use in the main PWM loop.

PWM Pulse Generation

	IF(RISING_EDGE(clk))THEN

	--1 Period = 512 Clock Cycles
		--Nevative Duty Cycle
		IF(pwm_cnt = 256-my_nums(int_cnt_0))THEN
			pwm_cnt := pwm_cnt + 1;
			LED_OUTPUT(9 DOWNTO 5) <= "00000";
			LED_OUTPUT(4 DOWNTO 0) <= "11111";
		--Positive Duty Cycle
		ELSIF(pwm_cnt = 256+my_nums(int_cnt_0))THEN
			pwm_cnt := 0;
			LED_OUTPUT(9 DOWNTO 5) <= "11111";			
			LED_OUTPUT(4 DOWNTO 0) <= "00000";
		ELSE
			pwm_cnt := pwm_cnt + 1;
		END IF;
		
		--Clk_Cnt here will set how fast the LEDs fade in and out.
		IF(clk_cnt = 500000)THEN
		
			--Increment
			IF(direction = 0)THEN
				IF(int_cnt_0 = 31)THEN
					direction := 1;
				ELSE
					int_cnt_0 := int_cnt_0 + 1;
				END IF;	
					clk_cnt := 0;
			--Decrement
			ELSE
				IF(int_cnt_0 = 1)THEN
					direction := 0;
				ELSE
					int_cnt_0 := int_cnt_0 - 1;
				END IF;	
					clk_cnt := 0;			
			END IF;
					
		ELSE	
			clk_cnt := clk_cnt + 1;
		END IF;	
	
	END IF;

           After all that wire wrapping and code writing, let's program the CPLD and see how well it works!