boolean pinState;

byte interruptPin = 19;
volatile boolean pinStateChanged = false;
volatile uint32_t overflowCounter = 0;

volatile uint32_t us;

void setup()
{
  noInterrupts();

  pinMode(interruptPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(interruptPin), on_change_state, CHANGE);

  Serial.begin(2000000);

  Serial.println(F(" Arduino Mega overflow interrupts"));
  //Serial.println(digitalPinToInterrupt(interruptPin));

  // Set timer1
  TCCR1A = 0;
  TCCR1B = 0;

  TCCR1B |= (1 << CS10); // No prescaler

  TIMSK1 |= (1 << TOIE1); // enable timer overflow interrupt ISR(TIMER1_OVF_vect)

  OCR1A = 65535; // compare match register


  // enable timer compare interrupt, reset if function not exist
  //TIMSK1 |= (1 << OCIE1A);


  //TCCR1A |= (1 << WGM11);  // WGM 2 (CTC)
  //TCCR1A = (1 << COM1B0);  // Toggle OC1B on overflow

  //TCCR1B |= (1 << WGM12); // CTC mode

  //TCCR1B |= (1 << CS10); // Continue counting in TCNT1
  TCNT1 = 0; // preload timer


  _NOP();
  _NOP();
  _NOP();
  _NOP();
  _NOP();

  volatile uint16_t t1 = TCNT1; // 2 cycles
  //TCCR1B |= (1 << CS10); // Continue counting in TCNT1
  volatile uint16_t t2 = TCNT1;
  //TCCR1B &= ~(1 << CS10); // Stop counting in TCNT1
  volatile uint16_t t3 = TCNT1;

  Serial.println(t1);
  Serial.println(t2);
  Serial.println(t3);

  interrupts();
  us = micros();

  overflowCounter = 0;
  TCNT1 = 0;
  TCCR1B |= (1 << CS10); // Continue counting in TCNT1
}

// interrupt service routine that wraps a user defined function supplied by attachInterrupt
ISR(TIMER1_OVF_vect)
{  
  overflowCounter++;
}

void on_change_state() {
  pinStateChanged = true;
}

void loop()
{

  //if (micros() - us >= 500000)
  //  pinStateChanged = true;


  if (pinStateChanged)
  {

    uint16_t cnt = TCNT1;
    TCNT1 = 0;

    uint32_t ovf = overflowCounter;
    overflowCounter = 0;

    pinStateChanged = false;

    uint32_t t = micros();
    us = t - us;

    Serial.print("OVF: ");
    Serial.print(ovf);
    Serial.print(" CNT: ");
    Serial.print(cnt);

    //pinState = digitalRead(interruptPin);

    // For Arduino Mega 2560 and pin 19, related chip pin is PD2.
    // Following should generate the same machine code
    // pinState = PIND & (1 << PD2);
    pinState = bitRead(PIND, PD2);

    if (pinState)
      Serial.print(F(" HIGH "));
    else
      Serial.print(F(" LOW  "));


    uint32_t cycles = ((uint32_t)ovf << 16) + cnt;

    Serial.print(cycles);
    Serial.write(' ');

    Serial.print( (uint32_t) ((uint64_t)cycles * 625 / 10));
    Serial.print("ns");

    Serial.write(' ');

    Serial.print(us);
    Serial.print("us");
    Serial.println();

    us = t;

  }
};