source: avrstuff/V-USB_Dev/firmwares/christmas/main.c@ 4946f6f

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <avr/pgmspace.h>
#include <util/delay.h>

#include <string.h>
#include <stdbool.h>

#include "usbdrv/usbdrv.h"

#define DDRIN DDRB
#define PORTIN PORTB
#define PININ PINB

#define DDROUT DDRC
#define PORTOUT PORTC

int state;
int step;

int main() {
//      wdt_enable(WDTO_2S);

        // USB
        sei();

        DDROUT = 255; // Keyboard matrix out
        PORTOUT = 255; // Enable pull up
                // We put all pins as input then output a 0 in only one at a time.
                // All the other pins are high-Z to avoid short circuits when many
                // buttons are pressed.
        DDRIN = 0; // Keyboard matrix in
        PORTIN = 255; // Enable pull up

        state = 0;
        step = 0;

        for(;;) {
                switch(state)
                {
                        case 0:
                                for(int i = 5; --i>=0;) {
                                        PORTOUT = ~(1<<i);
                                        _delay_ms(100);
                                        PORTOUT = 255;
                                        _delay_ms(300);
                                }
                                _delay_ms(500);
                                break;
                        case 1:
#define PWM 10000
                                for(int j = PWM; j > 0; j -= 100)
                                {
                                        PORTOUT = 255;
                                        _delay_us(j);
                                        PORTOUT = 0;
                                        _delay_us(PWM - j);
                                }
                                for(int j = PWM; j > 0; j -= 100)
                                {
                                        PORTOUT = 0;
                                        _delay_us(j);
                                        PORTOUT = 255;
                                        _delay_us(PWM - j);
                                }

                                _delay_ms(500);
                                break;

                        case 2:
                                for(int i = 16; --i>= 0;)
                                {
                                        PORTOUT = i;
                                        _delay_ms(200);
                                }
                                break;

                        case 3:
                                for(int j = PWM; j > 0; j -= 100)
                                {
                                        PORTOUT = ~3;
                                        _delay_us(j);
                                        PORTOUT = 3;
                                        _delay_us(PWM - j);
                                }
                                for(int j = PWM; j > 0; j -= 100)
                                {
                                        PORTOUT = 3;
                                        _delay_us(j);
                                        PORTOUT = ~3;
                                        _delay_us(PWM - j);
                                }

                                _delay_ms(500);
                                break;

                        default: state = 0;
                }

                if (++step > 5) {
                        step = 0;
                        ++state;
                }
        }
}