void init_port();
void init_timer();

void setup() {
  init_port();
  init_timer();
  sei(); // Enable global interrupts
}

void loop() {
  // Main code, can be left empty as the ISR handles the LED toggling
}

void init_port() {
  DDRD |= (1 << PD4); // Set PD4 as an output pin
}

void init_timer() {
  // Configure Timer1 in CTC mode (WGM12 set, WGM10 and WGM11 cleared)
  TCCR1A = 0; // Clear WGM11 and WGM10, no need to set these in CTC mode
  TCCR1B = (1 << WGM12); // Set WGM12 for CTC mode

  // Set prescaler to 1024
  TCCR1B |= (1 << CS12) | (1 << CS10);

  // Set the compare value for 1 second at 16 MHz clock
  OCR1A = 15624;

  // Enable Timer1 compare match interrupt
  TIMSK1 = (1 << OCIE1A);

  // Clear the timer counter
  TCNT1 = 0;
}

// ISR for Timer1 Compare Match A
ISR(TIMER1_COMPA_vect) {
  PORTD ^= (1 << PD4); // Toggle PD4 (LED)
}