Support for GNSS modules with different baudrates

[Grumium]

Hi.
In a project, I am currently using the following GNSS module with a NEO-M9N chip.
https://docs.m5stack.com/en/module/GNSS%20Module
The baud rate is fixed at 38400 bps, which makes the current GPS sensor driver incompatible as it is hardcoded for 9600 bps. To address this, I modified the xsns_60_GPS.ino file based on the structure of xnrg_14_bl09xx.ino. The update allows you to specify baud rates (4800/9600/19200/38400) as a parameter passed along with GPS_RX in the template:

void UBXDetect(void)
{
  UBX.mode.init = 0;
  if (PinUsed(GPIO_GPS_RX, GPIO_ANY) && PinUsed(GPIO_GPS_TX)) {
    UBX.mode.baudrate = 4800;
    UBX.mode.rx_pin = Pin(GPIO_GPS_RX, GPIO_ANY);
    uint32_t baudrate = GetPin(UBX.mode.rx_pin) - AGPIO(GPIO_GPS_RX);  // 0 .. 3
    UBX.mode.baudrate <<= baudrate;        // Support 1 (4800), 2 (9600), 3 (19200), 4 (38400)
    UBXSerial = new TasmotaSerial(UBX.mode.rx_pin, Pin(GPIO_GPS_TX), 1, 0, UBX_SERIAL_BUFFER_SIZE); // 64 byte buffer is NOT enough
    if (UBXSerial->begin(UBX.mode.baudrate)) {
      DEBUG_SENSOR_LOG(PSTR("UBX: started serial at %d bps"), UBX.mode.baudrate);
      if (UBXSerial->hardwareSerial()) {
        ClaimSerial();
        DEBUG_SENSOR_LOG(PSTR("UBX: claim HW"));
      }
#ifdef ESP32
      AddLog(LOG_LEVEL_DEBUG, PSTR("UBX: Serial UART%d at %d bps"), UBXSerial->getUart(), UBX.mode.baudrate);
#endif
    }

This change improves compatibility and flexibility for UBX-compatible GNSS modules.
If there are no further suggestions, I would like to make PR involving changes in xsns_60_GPS.ino and tasmota_template.h
Eventually, the new functionality should be mentioned in the docs https://tasmota.github.io/docs/GPS-NTP-server/#tasmota-settings

[arendst]

Great. Pls continue with PR.

[s-hadinger]

Thanks for this proposal. I'm afraid it's contrary to the convention of the GPIO type suffix. They are primarily meant at having multiple instances of the same feature.
Your proposal makes it unfortunately counter-intuitive and limitative for the future.

I suggest you add either a command or a settings options to choose the serial baud rate.

[Grumium]

Well, it has been used before in the exact same way, so is there really a convention?

Tasmota/tasmota/tasmota_xnrg_energy/xnrg_14_bl09xx.ino

Lines 389 to 395 in 5cbe5fe

	else if (PinUsed(GPIO_BL0942_RX, GPIO_ANY)) {
	Bl09XX.model = BL0942_MODEL;
	Bl09XX.rx_pin = Pin(GPIO_BL0942_RX, GPIO_ANY);
	uint32_t option = GetPin(Bl09XX.rx_pin) - AGPIO(GPIO_BL0942_RX); // 0 .. 7
	Bl09XX.support_negative = (option > 3); // 4 .. 7
	uint32_t baudrate = option & 0x3; // 0 .. 3 and 4 .. 7
	Bl09XX.baudrate <<= baudrate; // Support 1 (4800), 2 (9600), 3 (19200), 4 (38400)

Is there a huge risk of having to deal with two GNSS modules connected to one microcontroller? I don't see the application.
What is your suggestion? Remove it from the other driver and make it a command? I mean, at the end a little consistency would be nice.

Also @sfromis mentioned this counter-intuitive feature in a thread last year and it didn't raise any eyebrows. #7447 (comment)

[arendst]

Continue with your PR as suggested (Add indexes for baudrate selection)

[Grumium]

Done #22873

[Jason2866]

Iirc there is the possibility to change the baudrate of the GPS module. No code change in Tasmota needed.

[Grumium]

Oh, you mean the GNSS module itself, yes. Of course that is possible. But I am afraid an end-user wants to use the product as is and not hack into it.

Also, from the integration manual https://content.u-blox.com/sites/default/files/NEO-M9N_Integrationmanual_UBX-19014286.pdf p.25

The default baud rate is 38400 baud. To prevent buffering problems it is recommended not to
run at a lower baud rate than the default.

[Jason2866]

I have a GPS module running for years at 9600 baud. There is no issue at all.
Changing to 38400 will brake current installations.

[Grumium]

Perfect, many thanks to @arendst for the super speedy implementation in 53dee5b. I can confirm that it is working now without affecting the defaults.