avr blink program

blink.c

#define F_CPU 10000000UL
#include <avr/io.h>
#include <avr/interrupt.h>

#define BLINKPIN (1 << DDA0)

int main(void) {
        DDRA = BLINKPIN;
        PORTA = DDRA;

        // disable Interrupts in order to setup
        // timer interrupts
        cli();

        // enable compare mode
        TCCR1A = (1 << WGM01);
        // prescaler 1024
        TCCR1B = CS12 | CS10;

        // around 10Hz
        OCR1A = 975;
        // enable compare
        TIMSK |= (1 << OCIE1A);

        // avtivate interrupts again
        sei();

        while(1)
                ;
        return 0;
}


ISR (TIMER1_COMPA_vect) {
        PORTA ^= BLINKPIN;
}