int buttonPin = 3;
void setup()
{
  pinMode(buttonPin, INPUT_PULLUP);
  Serial.begin(9600);
  Serial.println("ready!");
  TCCR2B = 0x07; // clock frequency / 1024
  //OCR2B = 0x00;  // Output compare
  TCNT2 = 0;     // Set counter 2 to zero
  TIMSK2 = 0x01; // Enable overflow interrupt
  attachInterrupt(digitalPinToInterrupt(3), button_ISR, RISING);


}

void loop()
{

}


void button_ISR()
{
  Serial.print("button_ISR()");
  Serial.print("\n");
}

ISR(TIMER2_OVF_vect) {}