#define TICK_RATE 1000

uint32_t volatile count = 0;


void startCounting()
{
  // reset Timer 2
  TCCR2A = 0;
  TCCR2B = 0;

  // Timer 2 - gives us our 1 ms counting interval
  // 16 MHz clock (62.5 ns per tick) - prescaled by 128
  //  counter increments every 8 µs.
  // So we count 125 of them, giving exactly 1000 µs (1 ms)
  TCCR2A = bit(WGM21) ;   // CTC mode
  OCR2A  = 125 - 1;       // count up to 125 (zero relative !!!!)

  // Timer 2 - interrupt on match (ie. every 1 ms)
  TIMSK2 = bit(OCIE2A);   // enable Timer2 Interrupt

  TCNT2 = 0;      // Counter to zero

  // Reset prescalers
  GTCCR = bit(PSRASY);        // reset prescaler now
  // start Timer 2
  TCCR2B =  bit(CS20) | bit(CS22) ;  // prescaler of 128

}  // Ready to roll !!!

//******************************************************************
//  Timer2 Interrupt Service is invoked by hardware Timer 2 every 1 ms = 1000 Hz
//  16Mhz / 128 / 125 = 1000 Hz

ISR(TIMER2_COMPA_vect)
{
  static uint16_t timerTicks  = 0;

  // see if we have reached timing period
  if (++timerTicks >= TICK_RATE)
  {
    timerTicks = 0;              // reset interrupt counter

    digitalWrite(LED_BUILTIN, HIGH);
    interrupts();
    Serial.println(count);
    digitalWrite(LED_BUILTIN, LOW);
  }
}  // end of TIMER2_COMPA_vect

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);  // configurer la broche de la LED comme sortie
  digitalWrite(LED_BUILTIN, LOW);

  while (!Serial)
  {
    ;  // wait for serial port to connect. Needed for native USB port only
  }
  Serial.println("Timer Interrupt LED Blink V2");
  Serial.println("Type 'Pxxx' to set Period (ms) & 'Wxxx' to set Width (ms)");
  Serial.println("Enjoy !!!");

  startCounting();
} // end of setup

void loop() {
  // put your main code here, to run repeatedly:
  count++;
}