Bit timing inaccurate with multi threading

[ssharks]

The bit timing is arranged with delayMicroseconds(500);. On a single threaded application this works reasonable stable although rounding errors tend to accumulate.
As soon as multiple threads are used on an ESP32 or ESP8266, this is no longer guaranteed to take 500 us. Depending on the OS scheduling this causes some communication to work, sometimes not to work.

Would it be better to use a timer for the bit timing? This guarantees the bit timing independent of scheduling and does not accumulate timing errors.

A workaround on the ESP32: Ensure all Opentherm communication is on 1 core, ensure the parrallel tasks are running on the other core.

[Laxilef]

delayMicroseconds() blocks the core, unlike delay() which calls vTaskDelay():

void ARDUINO_ISR_ATTR delayMicroseconds(uint32_t us) {
  uint64_t m = (uint64_t)esp_timer_get_time();
  if (us) {
    uint64_t e = (m + us);
    if (m > e) {  //overflow
      while ((uint64_t)esp_timer_get_time() > e) {
        NOP();
      }
    }
    while ((uint64_t)esp_timer_get_time() < e) {
      NOP();
    }
  }
}

[ssharks]

Thank for the suggestion. vTaskDelay() does not work in this situation as the resolution for vTaskDelay() is either 1 or 10 ms, which prohibits from implementing a 0.5 ms delay.

A more accurate time is achievable using the timers of the ESP32, like with https://docs.espressif.com/projects/arduino-esp32/en/latest/api/timer.html

[Laxilef]

delayMicroseconds() does not call vTaskDelay().