Calling tone in loop freezes the Arduino

[jgromes]

Hi,

I have ran into a bit of an issue that calling tone in a loop will crash/hang/freeze Arduino Nano 33 BLE. Here's a simple sketch to replicate:

void setup() {
  Serial.begin(9600);
  while(!Serial);
  
  pinMode(6, OUTPUT);

  Serial.println("beep :)");
  int start = millis();
  while(millis() - start < 30000) {
    tone(6, 2200);
    delayMicroseconds(833);
    tone(6, 1200);
    delayMicroseconds(833);
  } // after a couple of seconds, pin 6 stops outputting anything (checked with a scope)

  noTone(6);
  Serial.println("no beep :("); // never gets printed
}

void loop() {

}

My initial theory was that this is caused by a failed dynamic allocation here:

ArduinoCore-mbed/cores/arduino/Tone.cpp

Lines 50 to 57 in 64bf2aa

	void tone(uint8_t pin, unsigned int frequency, unsigned long duration) {
	if (active_tone) {
	delete active_tone;
	}
	Tone* t = new Tone(digitalPinToPinName(pin), frequency, duration);
	t->start();
	active_tone = t;
	};

However, adding a check to make sure t != NULL didn't fix this, so now I'm no longer so sure. I don't know the platform well enough to attempt to fix this.

Background: this popped up in one of my projects (jgromes/RadioLib#407), when generating 1200/2200 Hz tones for AX.25 transmission. I was able to work around the issue by using PwmOut and switching the frequency of that.