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arduinoavratmegapwm

Arduino Mega2560 reboots after two consecutive calls to analogWrite

Why does this code lead to Arduino Mega2560 constantly resetting?

void setup() {
  Serial.begin(9600);
  Serial.println("SETUP");
  delay(500);             //without this line Serial prints "SESESESESE"
  analogWrite(10, 100);
  analogWrite(11, 50);    //reboots after this line
}

void loop() {
  Serial.println("LOOP"); //doesn't reach here
}

Arduino serial outputs the following:

SETUP
SETUP
SETUP
SETUP
SETUP
SETUP
SETUP
SETUP

Things to note:

1) Arduino does not reboot if I substitute pins 10 and 11 with some others (8 and 9 for example), but it does also reboot with pins 12 and 13 (I guess pins 10-13 are somehow special).

2) Arduino does not reboot if I use equal values in the calls to analogWrite (100 and 100 for example).

Solution

  • Apparently, the compiler's optimizations are to blame. After adding these two lines at the start of the program it finally works as it should:

    void setup() __attribute__((optimize("-O1")));
void loop() __attribute__((optimize("-O1")));