Intermittent i2c slave mode errors, interrupts delayed or fired in the wrong order resulting in data corruption

[chrisckc]

Hi, I have been using your very useful library to create some test code to try and get to the bottom of an issue I originally encountered using I2C slave mode with Arduino-Pico.

I recreated a test scenario using pure SDK and your library and found similar issues, the issues are fully detailed in this post along with scope traces.
raspberrypi/pico-sdk#1102

The issues are only really noticeable at I2C bus speeds above 100KHz.
Earle Philhower added a recent commit to his Arduino-Pico Wire API implementation which provides a workaround for the bulk of the issues, getting the failure rate down to around 0.02%, from originally being up to 50% at 1Mhz bus speed. (fast mode plus)

It looks to me like the remaining issues are with the SDK or maybe the hardware.