Atmega328 blink :-)

#define F_CPU 16000000ul
#include <util/delay.h>
#define LED PB5
#define LED_ON  PORTB |= (1<<LED)
#define LED_OFF PORTB &= ~(1<<LED)
#define LED_TGL PINB |= (1<<LED)

int main()
{
    DDRB |= (1<<LED);
    while(1)
    {
        LED_TGL;
        _delay_ms(500);
    }
}