#define F_CPU 16000000UL
#include <avr/io.h>
#include <avr/interrupt.h>
void delay(double td)  {
    // set up timer with prescaler = 64 and CTC mode
    TCCR1B |= (1 << WGM12)|(1 << CS12)|(1 << CS10);
    TCNT1 = 0;  // initialize counter
    OCR1A = (uint16_t) td*F_CPU/1024.0-1.0;
    TIMSK1 |= (1 << OCIE1A);    // enable compare interrupt
    sei();                      // enable global interrupt
}
int main(void) {
    DDRB |= (1 << PB0); // connect led to pin PC0
    delay(1.0);
    while(1) {};
}
ISR (TIMER1_COMPA_vect)
{
    PORTB ^= (1 << PB0); // toggle led here
}