//Overflow itnerrupt
ISR(TIMER0_OVF_vect)
{
    clock_datetime += 1;
    //    TIFR0 |= (1<<TOV0);
}

//Initialise the clock
void clock_init()
{
    cli(); // disable all interrupts
    TCCR1B = 0; // disable ticking
    TIMSK = (TIMSK & ~(0x3c)) | 0x04; // enable overflow interrupt
    TCNT1H = 0; // reset counter
    TCNT1L = 0;
    ICR1H = 40000U >> 8; // set overflow value
    ICR1L = 40000U & 0xff;
    TCCR1A = 0xfe; // 11 11 11 10, set channel config
    TCCR1B = 0x1a; // 00011010 start ticking
    sei(); // reenable interrupts

}