blinkInterruptSpeed.ino

int ledpin = PORTB5;

void setup() {
  // put your setup code here, to run once:
  DDRB = _BV(ledpin); //Set up LED pin as output
  Serial.begin(115200);

  TCCR1A = _BV(COM1A0); //Mode will be CTC; WGM12 is in B register
  TCCR1B = _BV(WGM12) | _BV(CS12) | _BV(CS10); //Set up x1024 prescaler
  OCR1A = 0x3333;
  TIMSK1 = _BV(OCIE1A); //Enable overflow interrupt

  interrupts(); //Enable interrupts globally
}

void loop() {
}

ISR(TIMER1_COMPA_vect){   //Timer1 Comp Interrupt
  Serial.println("Hello!");
  PORTB ^= _BV(ledpin);
}