// Arduino Timer 1 CTC Mode Example

// Initialize Timer 1 for CTC mode
void timer1CTC_Init(int max_count, int my_div) {
  TCCR1A = 0;            // Clear all bits in TCCR1A
  TCCR1B = 0;            // Clear all bits in TCCR1B
  OCR1A = max_count - 1; // Set the compare match register value
  TCNT1 = 0;             // Reset the counter
  TIFR1 = 0x7;           // Clear all interrupt flags
  TIMSK1 = (1 << OCIE1A); // Enable Timer 1 compare match A interrupt

  // Set CTC mode (WGM12 = 1)
  TCCR1B |= (1 << WGM12);

  // Set prescaler
  switch (my_div) {
    case 1:
      TCCR1B |= (1 << CS10);
      break;
    case 8:
      TCCR1B |= (1 << CS11);
      break;
    case 64:
      TCCR1B |= (1 << CS11) | (1 << CS10);
      break;
    case 256:
      TCCR1B |= (1 << CS12);
      break;
    case 1024:
      TCCR1B |= (1 << CS12) | (1 << CS10);
      break;
  }
}

void setup() {
  // Set PB5 (Pin 13 on Arduino Uno) as output
  pinMode(13, OUTPUT);

  // Initialize Timer 1 with a frequency of 2 Hz
  // 31250 is the value for OCR1A to achieve 2 Hz with prescaler 256
  timer1CTC_Init(31250, 256);
}

void loop() {
  // The main loop does nothing, the interrupt handles the LED toggling
}

// Timer 1 Compare Match A interrupt service routine
ISR(TIMER1_COMPA_vect) {
  PORTB ^= (1 << PORTB5); // Toggle the LED connected to PB5 (Pin 13 on Arduino Uno)
}