// code is in main.S
void setup() {
  DDRB |= (1 << PB5);

  TCCR1A = 0;

  TCCR1B &= ~(1 << WGM13);
  TCCR1B |= (1 << WGM12);
  
  TCCR1B |= (1 << CS12);
  TCCR1B &= ~(1 << CS11);
  TCCR1B &= ~(1 << CS10);

  TCNT1 = 0;
  OCR1A = 62500;

  TIMSK1 = (1 << OCIE1A);

  sei();

}

void loop() {

}

ISR(TIMER1_COMPA_vect) {
  PORTB ^= (1 << PB5);
}