#include <avr/io.h>
#include <avr/interrupt.h>
  
// global variable to count the number of overflows
volatile uint8_t tot_overflow;
  
// initialize timer, interrupt and variable
void timer1_init()
{
    // set up timer with prescaler = 8
    TCCR1B |= (1 << CS11);
  
    // initialize counter
    TCNT1 = 0;
  
    // enable overflow interrupt
    TIMSK1 |= (1 << TOIE1);
  
    // enable global interrupts
    sei();
  
    // initialize overflow counter variable
    tot_overflow = 0;
}
  
// TIMER1 overflow interrupt service routine
// called whenever TCNT1 overflows
ISR(TIMER1_OVF_vect)
{
    // keep a track of number of overflows
    tot_overflow++;
  
    // check for number of overflows here itself
    // 61 overflows = 2 seconds delay (approx.)
    if (tot_overflow >= 61) // NOTE: '>=' used instead of '=='
    {
        //PORTC ^= (1 << 0);  // toggles the led
        PORTB ^= 0xC0;
        
        // no timer reset required here as the timer
        // is reset every time it overflows
  
        tot_overflow = 0;   // reset overflow counter
    }
}
  
int main(void)
{
    // connect led to pin PC0
    // DDRC |= (1 << 0);
    PORTB = 0x80;
    DDRB = 0xC0;
  
    // initialize timer
    timer1_init();
  
    // loop forever
    while(1)
    {
        // do nothing
        // comparison is done in the ISR itself
    }
}