#define F_CPU 16000000UL
#include <Arduino.h>
#include <avr/io.h>
#include <avr/interrupt.h>

void delay(double td) {

  TCCR1A = 0x00;
  TCCR1B = 0x00;
  double prescalar = 1024.0;

  // Set initial count (34286) so overflow happens after 2 seconds (prescaler 1024)
  TCNT1 = 0;
  OCR1A = td*F_CPU/prescalar -1.0;  // OCR1A = Td*fcpu/prescalar - 1 
  TCCR1B |= (1<<WGM12); // for CTC mode, we need (WGM12 =1, WGM10,11,13 =0)
  TCCR1B |= (1 << CS02) | (1 << CS10); // Prescalar is set to  1024
  while ((TIFR1 & (1 << OCF1A)) == 0);  // By default, OCF1A is 1. 
                                        // When the time count reaches the top, 
                                        // OCF1A will turn 0.
  TCCR1B = 0x00;
  TIFR1 |= (1<<OCF1A);  // By default, OCF1A is 1.
}

void setup() {
  DDRB = 0xFF;
  PORTB = 0x00;
}
void loop() {
  delay(0.5);  // Wait for 2 seconds
  PORTB = ~PORTB;
}