#include "util/atomic.h"


unsigned long mymillis = 0;

int main (void)
{
  const unsigned long eventInterval = 1000;
  unsigned long previousTime = 0;
  
  DDRB |= (1 << PB5); 
  
  TCCR1B |= (1 << WGM12);         // Configure timer 1 for CTC mode
  TIMSK1 |= (1 << OCIE1A);        // Enable CTC interrupt
  OCR1A = 7999;                   // Set CTC compare value to 1 Hz at 8 MHz AVR clock , with a prescaler of 256
  TCCR1B |= (1 << CS00);          // Start timer at F_CPU /256
  
  sei ();                  // Enable global interrupts
  
  while (1)
  {
      // Updates frequently
      unsigned long currentTime; 
      ATOMIC_BLOCK(ATOMIC_RESTORESTATE) currentTime = mymillis;
      // This is the event
      if (currentTime - previousTime >= eventInterval) {
        // Event code
        PINB = (1 << PB5); // toggle       
        // Update the timing for the next time around
        previousTime = currentTime;
      }
  }
}

ISR (TIMER1_COMPA_vect)
{
  mymillis++;
}