analogWrite crashes

[yann-l]

a simple program that use analogWrite makes the portenta crash. Here is an example sketch from khoih-prog here

#define LEDB_PIN            25

void setup()
{
  pinMode(LEDB_PIN, OUTPUT);

  Serial.begin(115200);
  while (!Serial);

  delay(100);

  Serial.print(F("\nStarting analogWrite_Crash on ")); Serial.println(BOARD_NAME);
  analogWrite(LEDB_PIN, 150);
}


void loop()
{
}

it prints "Envie M7" here.

[facchinm]

Hi @yann-l ,
LED* pins on Portenta are not natively PWM capable, so calling analogWrite on them will cause an error. You can use instead any pin marked as PWM from the documentation

[yann-l]

Ok indeed it work on pin 4 and 5 for example, but not on pin3 (PG_7). At least clearly not at the correct frequency / duty_cule.

Same wrong behaviour when I use PwmOut object.

[facchinm]

If you are using a core > 2.4.0 PwmOut (and thus analogWrite) work on pin3 with a limitation on the minimum frequency reachable (~720Hz when not underclocking the processor).
This is due to the pin not being configurable as a normal timer but only as high resolution timer.
@sebromero I couldn't find a link documenting this, can we add it to the docs asap?

[yann-l]

That more or less works :
analogWrite(3, val);
works for val in 1-255 range. But analogWroteWrite(3, 1) produces an output that is always HIGH instead of low. So no way to have an output always LOW with analogWrite on this pin. And using digitalWrite(3, 0) doesn't work once analogWrite has been used.

[facchinm]

I just retested it and indeed there's a bug with analogWrite(3,0) and analogWrite(3,255) , which respectively make the signal steady high and low (while it should be the opposite). Will open a standalone issue to target it.

digitalWrite(3, LOW) won't work since the PWM is still running and forcing the status of the pin. To get rid of a PWM, you need to call pinMode(3, OUTPUT); again before calling digitalWrite()

void setup() {
  // put your setup code here, to run once:
  analogWrite(3, 128);
  delay(1000);
  pinMode(3, OUTPUT);
  digitalWrite(3, LOW);
}

[sebromero]

This is due to the pin not being configurable as a normal timer but only as high resolution timer.

@facchinm does it apply only to PG_7 or to all PWM capable pins?

[facchinm]

Only pin3 (PG_7) and pin6 (PA_8) are connected to HRTIM. In fact, pin6 can also be used as a normal timer, but conflicts with PK_1 (same timer/channel combination) so we dafault to the HRTIM functionality