void init_port();
void init_timer();

void setup() {
  // Correctly call the initialization functions
  init_port();
  init_timer();
}

void init_port() {
  // Set Pin D4 (bit 4 of Port D) as output
  volatile char *portd_dir = (volatile char *)0x2A;
  *portd_dir = 0x10;  // Set bit 4 (Pin D4) as output
}

void init_timer() {
  // Timer registers
  volatile char *tccr1a = (volatile char *)0x80; // TCCR1A register
  volatile char *tccr1b = (volatile char *)0x81; // TCCR1B register
  volatile short *tcnt1 = (volatile short *)0x84; // TCNT1 (Timer1 counter)
  volatile short *ocr1a = (volatile short *)0x88; // OCR1A (Output Compare Register A)
  volatile char *timsk1 = (volatile char *)0x6F; // TIMSK1 (Timer Interrupt Mask)

  // Configure Timer1
  *tccr1a = 0x00;           // Normal mode, no special output
  *tccr1b = 0x0D;           // Set CTC mode (Clear Timer on Compare Match) and 1024 prescaler
  *tcnt1 = 0;               // Initialize the counter to 0
  *ocr1a = 15624;           // Compare match value for Timer1 (higher for longer delay)
  *timsk1 = 0x02;           // Enable Timer1 compare match interrupt (OCIE1A)
}

// Interrupt Service Routine (ISR) for Timer1 Compare Match A
ISR(TIMER1_COMPA_vect) {
  volatile char *portd_data = (volatile char *)0x2B; 
  *portd_data ^= 0x10;  // Toggle Pin D4 (bit 4 of Port D)
}

void loop() {
  // Empty loop, all actions handled in the ISR
}