#include <avr/io.h>
#include <util/delay.h>
 
// Some macros that make the code more readable
#define output_low(port,pin) port &= ~(1<<pin)
#define output_high(port,pin) port |= (1<<pin)
#define set_input(portdir,pin) portdir &= ~(1<<pin)
#define set_output(portdir,pin) portdir |= (1<<pin) 
 
#define LON	1
#define LOF	0
 
#define LED_COUNT	12
 
uint8_t led_table[] = 
{
	LOF, PB0, PB1,
	LOF, PB1, PB0,
	LOF, PB0, PB2,
	LOF, PB2, PB0,
	LOF, PB0, PB4,
	LOF, PB4, PB0,
	LOF, PB1, PB2,
	LOF, PB2, PB1,
	LOF, PB1, PB4,
	LOF, PB4, PB1,
	LOF, PB2, PB4,
	LOF, PB4, PB2
};
 
void clear_leds()
{
	set_input(DDRB, PB0);
	set_input(DDRB, PB1);
	set_input(DDRB, PB2);
	set_input(DDRB, PB4);
}
 
void set_led(uint8_t index, uint8_t state)
{
	uint8_t i = (index * 3);
 
	uint8_t s  = led_table[i];
	uint8_t p1 = led_table[i + 1];
	uint8_t p2 = led_table[i + 2];
 
	set_output(DDRB, p1);  
	set_output(DDRB, p2);
 
	if(state == LON)
	{
		output_low(PORTB, p1);
		output_high(PORTB, p2);
	}
	else
	{
		output_low(PORTB, p1);
		output_low(PORTB, p2);
	}
}
 
void delay_10us(uint8_t us)
{
	uint8_t delay_count = F_CPU / 2000000;
   	volatile uint8_t i;
 
   	while (us != 0) {
    	for (i=0; i != delay_count; i++);
     		us--;
   	}
 }
 
void do_pwm_fade(uint8_t index, uint8_t start_duty, uint8_t end_duty, uint8_t rate) 
{
	uint8_t duty;
   	uint8_t j;
 
   	duty = start_duty;
   	while (duty != end_duty) 
	{
    	for (j = 0; j < rate; j++) 
		{
       		set_led(index, LON);
       		delay_10us(duty);
       		set_led(index, LOF);
       		delay_10us(255-duty);
     	}
 
     	if (start_duty < end_duty) 
       		duty++;
		else 
       		duty--;
	}
}
 
int main(void) 
{
	// initialize the direction of the B port to be outputs
	// on the 3 pins that have LEDs connected
 
	while(1)
	{
		for(int i=0; i < LED_COUNT; i++)
		{
			clear_leds();
			do_pwm_fade(i, 0, 255, 1);
			do_pwm_fade(i, 255, 0, 1);
		}
	}
}