Support for I2C slave mode

[kdsoo]

I'm trying to run Adafruit esp8266 breakout as i2c slave using gpio 13 as scl and 14 as sda.
Going through the Wire library code, I found it inapplicable to run esp as i2c slave with changed pin configuration.
For ordinary use of Wire library for i2c slave configuration, we put slave address as Wire.begin() argument like "Wire.begin(address)"
But considering Wire.pins() deprecated, there is no way to change i2c pin configuration. Am I getting right?
So, how could I use esp as i2c slave with changed pin configuration?
Any pointer will be appreciated.

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[Links2004]

the ESP currently only support I2C master mode you can not run it in slave mode.

[kdsoo]

@Links2004 Thanks. I'll look for alternative interface to give commands to ESP.

[isparkes]

Is there an underlying reason not to implement slave mode, or is it just a "didn't get round to it yet" situation? If it's just a matter of priorities, I'd have a go at implementing slave mode...

[Links2004]

there is no technical limitation, simple no one has done it yet.

[isparkes]

OK, great. I need it for a project I am doing. If I can get it to work reliably, I'll make a pull request for it.

[francox-sg]

yes!!! i need this library for my proyect, esp i2c slave is a priority for the community, if not, i2c can´t be implemmented completely (sorry for my english)

[francox-sg]

and... i can´t install the new library version of esp arduino ide....

[isparkes]

I looked into this, and I don't see an easy way to do this at the moment. The SDK does not provide support for interrupts, and therefore the interrupt driven slave mode which requires this is not an easy implementation at the moment.

[Links2004]

there are interrupts, only for GPIO16 not.
we use them for attachInterrupt for example.
https://github.com/esp8266/Arduino/blob/master/cores/esp8266/core_esp8266_wiring_digital.c#L112
https://github.com/esp8266/Arduino/blob/master/cores/esp8266/core_esp8266_wiring_digital.c#L137
how fast you can go with simple use attachInterrupt needs to be tested.
but default I2C run at 100kHz or for high speed 400kHz, I think this is reachable.

[isparkes]

Yes, I see that now. I was kind of hoping that the SDK would bring support for Slave Mode, but it doesn't. However with the point you bring, I agree, it should be possible to implement it outside of the SDK.

[chrischsc]

I would be really interested in this. Any progress or investigations so far?