Teensy 4.x timer interrupt example using TimerTree

void myTimerInterrupt() {
  // TODO Your code goes here
  // The following functions may be useful here:
  // Timer3.start(); // Start counting & clear counter
  // Timer3.stop(); // => stop counting but do not clear counter
  // Timer3.restart(); // => clear counter
  // Timer3.resume(); // => Start, without clearing counter
}

void setup()
{
  Timer3.initialize(20000);
  Timer3.attachInterrupt(myTimerInterrupt);
  Timer3.start();
}