DIY DE0-Nano Breakout Board

The Software
           Now, let's take a look at the VHDL used to test out this breakout board. We're just blinking LEDs here so nothing too fancy. There's two main parts to the VHDL for this project.
    -PWM Generation
    -State Machine Shifter

           The PWM generation outputs 32 unique values, to a 32 bit std_logic_vector as seen below.

PWM Generation

		IF(pwm_cnt = my_nums(0))THEN			
			pwm_cnt := pwm_cnt + 1;
			led_buf(0) <= '0';
		ELSIF(pwm_cnt = my_nums(1))THEN			
			pwm_cnt := pwm_cnt + 1;
			led_buf(1) <= '0';
		ELSIF(pwm_cnt = my_nums(2))THEN			
			pwm_cnt := pwm_cnt + 1;
			led_buf(2) <= '0';
		ELSIF(pwm_cnt = my_nums(3))THEN			
			pwm_cnt := pwm_cnt + 1;
			led_buf(3) <= '0';
		...
		....
		....
		..
		ELSIF(pwm_cnt = my_nums(30))THEN			
			pwm_cnt := pwm_cnt + 1;			
			led_buf(30) <= '0';	
		ELSIF(pwm_cnt = my_nums(31))THEN			
			pwm_cnt := pwm_cnt + 1;
			led_buf(31) <= '0';				
	
		ELSIF(pwm_cnt = 256)THEN
			pwm_cnt := 0;
			led_buf <= (others => '1');
		ELSE
			pwm_cnt := pwm_cnt + 1;
		END IF;	

           The second part of the VHDL code is where we shift the PWM output between LEDs. Depending upon a specific count value, the std_logic_vector created from above, is shifted and set to the output LEDs. This creates a type of rain-drop or waterfall effect as one bright LED flows through the rest of the LEDs. The state machine is really just going through the 32 states over and over again, no tricks.

State Machine Shifter

		case current_state is
		 when S0 =>
			GPIO_0_D(31 downto 0) <= led_buf(31 downto 0);
		 when S1 =>
			GPIO_0_D(31 downto 0) <= led_buf(30 downto 0) & led_buf(31);
		 when S2 =>
			GPIO_0_D(31 downto 0) <= led_buf(29 downto 0) & led_buf(31 downto 30);
		..
		...
		...
		..
		 when S29 =>
			GPIO_0_D(31 downto 0) <= led_buf(2 downto 0) & led_buf(31 downto 3);								
		 when S30 =>
			GPIO_0_D(31 downto 0) <= led_buf(1 downto 0) & led_buf(31 downto 2);				
		 when S31 =>
			GPIO_0_D(31 downto 0) <= led_buf(0) & led_buf(31 downto 1);				
		end case;

           So with that simple VHDL code done, let's compile it and get it into the FPGA to finally test our breakout board.