atmega8 timer1 - use 16-bit compare with ICR (input capture interrupt) for long periods of time

atmega8_timer1.c

// All values/comments are valid with ATmega8 running at Fosc = 4.000MHz

#include <avr/io.h>
#include <avr/interrupt.h>

// TIMER1 with prescaler clkI/O/1024
#define TIMER1_PRESCALER      (1 << CS12) | (1 << CS10)

// ~15s (4MHz@1024 prescale value)
#define TIMER1_COMPARE_VALUE  0xE4E1


void main()
{
   // ... do something ...

   // init Timer1
   // use Fast PWM and ICR for compare mode (14) to get long periods
   TIMSK  |= (1 << TICIE1);                                    // set input capture interrupt enable
   TCCR1A |= (1 << WGM11);                                     // set Fast PWM mode with ICR1 as compare register
   TCCR1B |= (1 << WGM13) | (1 << WGM12) | TIMER1_PRESCALER;   // set Fast PWM mode with ICR1 as compare register
   ICR1H   = (TIMER1_COMPARE_VALUE >> 8);                      // set compare value for interrupt
   ICR1L   = (TIMER1_COMPARE_VALUE & 0xFF);                    // set compare value for interrupt
   sei();                        // global interrupt enable

   // ... do something ...

   while (1)
   {
      // ... do something ...

   } /* end of while(1)  */
}

// *** Interrupt Service Routine *****************************************

// Timer1 input capture interrupt (~15s 4MHz@1024 prescale factor)
ISR(TIMER1_CAPT_vect)
{
   // handle interrupt
}

Thankful
that was perfect