Allow user to call TwoWire::begin themselves

[Tasssadar]

• That way, they can use non-default pins and have multiple
  devices on a single TwoWire bus.

[caternuson]

To use non-default pins, create a Wire object with those and pass in that instance:
https://github.com/adafruit/Adafruit_BMP280_Library/blob/master/Adafruit_BMP280.h#L185

Can you clarify what you mean by having multiple devices? That is supported on any I2C bus as long as each device has a unique address.

[Tasssadar]

Let's say you connect two different sensors on one I2C bus.

You are supposed to only call Wire.begin() once1, and if the library calls it, you can't use two libraries that use I2C (because they both call begin()).

Also, on ESP32 with Arduino framework port, Wire.begin is used to set the I2C pins2, not the Wire constructor.

[ladyada]

you can def call Wire.begin() as many times as you like
ESP32/ESP8266 do it in an incompatible way that breaks every other platform, we dont allow that change in our libraries :)

[Tasssadar]

While you definitely can, I don't think you should. As far as I can tell, there are no guards against it anywhere in the Arduino core, so if there is any I2C transfer in progress already, the state will become corrupted.

From the code, it's clear TwoWire::begin() is not designed to be called multiple times, even though it might work in most trivial use cases.

I agree that ESP32's begin is "unofficial", but it's also not exactly unpopular platform to build stuff on, and I'd say it's a good idea to at least consider supporting it.

[ladyada]

we support esp32 just fine - but the Wire interface pins must be defined in the BSP like every other arduino :)
Wire.begin() must be able to be called multiple time - all arduino libraries will call wire.begin() - its 10 years too late to change.
Please ask the espressif team to keep compatibility, it isnt hard, and we must make sure our libraries work with all platforms

[ladyada]

thank you for the PR, but we will not be able to merge it

[Tasssadar]

I understand, thanks for considering it anyway :)

Wire.begin() must be able to be called multiple time - all arduino libraries will call wire.begin() - its 10 years too late to change.

Honestly, that's horrifying.

[JarekParal]

@ladyada

we support esp32 just fine - but the Wire interface pins must be defined in the BSP like every other arduino :)

Why constrain the user for one specific configuration when we have a super device as ESP32, where you can set almost each peripheral to any pin. Help us to move to 21. century in MCU development.

Wire.begin() must be able to be called multiple time - all arduino libraries will call wire.begin() - its 10 years too late to change.

Why you couldn't make a small step for improving the Arduino libraries by merging this PR in your library and make Arduino world a little bit better. This will not add you any other workload.

[ladyada]

@JarekParal have you opened an issue with esp32 asking them to make a new, non-conflicting function say setPins() ?