Trivial blink program for AVR microcontrollers. Useful for figuring out whether the fuses are set right. If not then the LED will blink at intervals other than one second.

blink.c

// To be compiled with:  (replace values if needed)
// avr-gcc -mmcu=atmega88 -DF_CPU=16000000UL blink.c -Os -oblink && avr-objcopy -O ihex blink.elf blink.hex

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

int main(void)
{
    DDRB |= 1<<DDB0;

    while (1) {
        _delay_ms(1000);
        PORTB = 0xff;
        _delay_ms(1000);
        PORTB = 0x00;
    }
}