Button Click & Hold (AVR)

gistfile1.c

#define BTN_DEBOUCE 20 //ms


ISR(INT0_vect) {
    uint16_t timer = 0;
    while(bit_is_clear(PIND, PD2)) { // button hold down
        timer++; // count how long button is pressed
        _delay_ms(1);
    }
    if(timer > BTN_DEBOUCE) { // software debouncing button
        if(timer < 500UL) {//unsigned long
            //single click
            printString("single click");
        } else {
            //button hold
            printString("hold down");
        }
    }
}

void initInterrupt0(void) {
    GIMSK |= (1 << INT0); // general interrupt mask register -> enable interrupt on INT0
    MCUCR &= ~(1 << ISC00); // trigger interrupt on falling edge
    MCUCR |= (1 << ISC01); // trigger interrupt on falling edge
    sei(); //  set interrupt enable bit
}

Hello. Never use delay function in ISR. It is really bad practice, that can cause hard to debug problems.