// Failed counnting cycles in WOKWI
// On real ATmega2560 is 16 cycles, with simulator is 17

void startTimer1 ()
{
  // reset Timer 1
  TCCR1A = 0;
  TCCR1B = 0;

  TCNT1 = 0;            // reset counter
  TIFR1 |= bit (TOV1);  // clear overflow flag

  // start Timer 1
  TCCR1B =  bit (CS10); //  no prescaler
}

void setup ()
{
  delay(100);
  Serial.begin (115200);
  Serial.println ();

  Serial.print (F("Frequency: "));
  Serial.print (F_CPU);
  Serial.println (F("Hz"));

  Serial.println ("Cycles, ns");

}

void loop ()
{
  
  cli();

  startTimer1 ();

  // 16x NOP

  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();
 
  volatile uint16_t cy = TCNT1;

  sei();

  cy -= 1; // correction

  volatile uint32_t ns10 = (uint32_t)cy * 625;
  
  Serial.print (cy);
  Serial.write (',');
  Serial.write (' ');
  Serial.print (ns10 / 10);
  Serial.write ('.');
  Serial.println (ns10 % 10);
  Serial.flush ();
}