main.c

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

int main(void) {
    DDRB = 0b11111111;

    while (1) {
        PORTB = 0b11111111;
        _delay_ms(1000);
        PORTB = 0b00000000;
        _delay_ms(1000);
    }

    return (0);
}