#define LED_PIN 13  // Built-in LED is on pin 13

void setup() {
  // Set pin 13 as output
  asm volatile (
    "sbi %[ddr], %[pin] \n"  // Set bit in DDRB register to configure pin as output
    : 
    : [ddr] "I" (_SFR_IO_ADDR(DDRB)), [pin] "I" (5)  // DDRB corresponds to digital pins 8-13
  );
}

void loop() {
  // Turn the LED on
  asm volatile (
    "sbi %[port], %[pin] \n"  // Set bit in PORTB register to turn on the LED
    : 
    : [port] "I" (_SFR_IO_ADDR(PORTB)), [pin] "I" (5)  // PORTB, pin 5 = digital pin 13
  );
  delay(500);  // Wait for 500ms

  // Turn the LED off
  asm volatile (
    "cbi %[port], %[pin] \n"  // Clear bit in PORTB register to turn off the LED
    : 
    : [port] "I" (_SFR_IO_ADDR(PORTB)), [pin] "I" (5)
  );
  delay(500);  // Wait for 500ms
}