#ifndef F_CPU
#define F_CPU 16000000UL // 16 MHz clock speed
#endif
#define ever (;;)

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

int main(void)
{
    DDRB = 0xFF;         // Define PORTB as Output

    for ever {           // Infinite loop
        PORTB = 0xFF;    // Turns ON all LEDs
        _delay_ms(1000); // 1 second delay
        PORTB = 0x00;    // Turns OFF all LEDs
        _delay_ms(1000); // 1 second delay
    }
}