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

#define BLINK_DELAY_MS  1000

int main (void)
{
    /*  set pin 25 of PORTB for output*/
    DDRA |= _BV(DDA3);

    while (1) {
        /*  set pin 25 high to turn led on  */
        PORTA |= _BV(PORTA3);
        _delay_ms(BLINK_DELAY_MS);
        /*  set pin 25 low to turn led off */
        PORTA &= ~_BV(PORTA3);
        _delay_ms(BLINK_DELAY_MS);
    }
}