#define F_CPU 1000000UL
#include <avr/io.h>
#include <util/delay.h>

void sirena (int cislo){
	while (cislo >= 0){
		_delay_us(1);
		cislo --;
	}
}

int main(void){
	DDRD = 0xFF;
	while(1){
		for (int i = 1; i<=500; i++) {
		PORTD = 0b00000000;
		sirena (i);
		PORTD = 0b10000000;
		sirena(i);
		}
		for (int i = 500; i>=1; i--) {
			PORTD = 0b00000000;
			sirena (i);
			PORTD = 0b10000000;
			sirena(i);
		}
	}
return 0;
}