aufgabe-2.c

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

int counter = 0;

ISR (TIMER0_COMP_vect)
{
  PORTA = 1 << ((counter++ >> 6) & 7);
}

int main (void)
{
  cli ();
  TCCR0 = (1 << CS01) | (1 << CS00);
  TIMSK = 1 << OCIE0;
  sei ();
  DDRA = 0xff;
  while (1);
  return 0;
}