The hello world of avr-c

blink.c

#define F_CPU 16000000L

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

int
main (void)
{
    DDRB |= _BV(DDB0);

    while(1)
    {
        PORTB ^= _BV(PB0);
        _delay_ms(500);
    }
}