c

#include <avr/io.h>
#include <avr/interrupt.h>

void warten(void) {
	while ( !(TIFR1 & (1 << OCF1A ) ) ) 
	;
	TIFR1 |= (1 << OCF1A ); 
}

ISR(TIMER1_COMPA_vect) {
	PORTB = 0;
}

ISR(TIMER1_OVF_vect) {
	PORTB ^= 8;
}

int main(void) {
	
	DDRB = 8;
	PORTB = 0;
	TCCR1B = (1 << CS10) ; //prescale 1
	
	OCR1A = (16000000 / 2 / 1 / 440) - 1;
	
	TIMSK1 |= (1 << OCIE1A) | (1 << TOIE1);
	PCICR = 0x01;
	sei();
	
	while(1) {
	};
}