Strange behavior in TwoWire in Slave Mode

[camelator]

Describe the bug
it looks like not possible to directly use TwoWire in slave mode. in this case the rxbuffer is never fill.
There is a différence in having an empty user receive handler and not having a receive handler. In the first case rxbuffer is fill correctly in the second case it is not fill.

Having:
TwoWire myI2C(PB7, PB6);
setup:
myI2C.begin(0x18) ;
in this case myI2C.available() is never > 0.

to have myI2C.available() > 0 when a message is received you must have implemented:
myI2C.onReceive(onReceiveHandler);

onReceiveHandler may be an empty code {}

in this situation TwoWire works correctly.

To Reproduce
TwoWire myI2C(PB7, PB6);
setup:
myI2C.begin(0x18) ;
loop:

if (myI2C.available()>0)
{
...
}

to make the program works:

setup:

myI2C.begin(0x18) ;
myI2C.onReceive(onReceiveHandler);


void onReceiveHandler(int howMany) {
  }

[fpistm]

Hi @camelator
I don't see the issue you have, to provide the receive handler/event function.
https://docs.arduino.cc/language-reference/en/functions/communication/wire/onReceive/

You can also see the example:

Arduino_Core_STM32/libraries/Wire/examples/slave_receiver/slave_receiver.ino

Line 18 in 93d2c96

Wire.onReceive(receiveEvent); // register event

[camelator]

it is an issue with regards to the Arduino documentation, because if the onReceiveHandler is not set, no data is received. see interrupt on the twowire class.