#include <avr/io.h>
#include <util/delay.h>

#define LED_PIN     PB5 // Pin 13 on most Arduino boards

void setup() {
    // Set LED pin as output
    DDRB |= (1 << LED_PIN);
}

int main() {
    setup();
    
    while (1) {
        // Turn on the LED
        PORTB |= (1 << LED_PIN);
        
        // Delay for 250 ms
        _delay_ms(250);
        
        // Turn off the LED
        PORTB &= ~(1 << LED_PIN);
        
        // Delay for 250 ms
        _delay_ms(250);
    }
    
    return 0;
}