Puzzled by ESP32 timers and mutex

Projects Programming
14

I've verified that what you said is correct by adding some code to loop() to check if millis() changes in the critical section:

void loop() {
  static uint32_t totalCount = 0;
  portENTER_CRITICAL(&timerMux); // Ensure loop() and onTimer() don't access shared data at the same time
    uint32_t onTimerCountSample1 = onTimerCount;
    uint32_t millisSample1 = millis();
    delay(100); // To make sure onTimer() is called whilst mutex is locked.
    uint32_t millisSample2 = millis();
    Serial.print("onTimerCount ");
    if(onTimerCount == onTimerCountSample1){
      Serial.print("didn't change ");
    }
    else{
      Serial.print("changed by ");
      Serial.print(onTimerCount-onTimerCountSample1);
    }
    Serial.print(" : millis() ");

    if(millisSample1 == millisSample2){
      Serial.print("didn't change ");
    }
    else{
      Serial.print("changed by ");
      Serial.print(millisSample2-millisSample1);
    }
    Serial.println(" in loop's critical section");
    totalCount+= onTimerCount;
    onTimerCount = 0;
  portEXIT_CRITICAL(&timerMux); // onTimer() can now access shared data
  Serial.print("totalCount = ");
  Serial.println(totalCount);
  delay(900); // To make total delay ~1 second
}

Serial monitor output:

onTimerCount didn't change  : millis() didn't change  in loop's critical section
totalCount = 0
onTimerCount didn't change  : millis() didn't change  in loop's critical section
totalCount = 1000
onTimerCount didn't change  : millis() didn't change  in loop's critical section
totalCount = 2000
onTimerCount didn't change  : millis() didn't change  in loop's critical section
totalCount = 3000

This topic, post#2 says delay() just returns if interrupts are off.