transfer_in_progress gets stuck to true sometimes at higher bus speeds

[renzenicolai]

Hello! First of all thank you for creating this awesome library.
We've used it in the firmware for an open source device we're building (https://github.com/badgeteam/mch2022-firmware-rp2040/tree/renze/i2c-debug).

We're encountering a problem: if we talk to the RP2040 at low speeds (8kHz bus speed) everything is stable but once we increase the bus speed to 100kHz (or 400kHz) we found that the RP2040 can get into a state where slave->transfer_in_progress gets stuck high until a new transfer is started from the bus master.

We're using that flag to implement a simple form of locking on the register map, preventing registers to be used by the firmware until the transfer is done. Thus when it gets stuck on true the firmware doesn't handle requests anymore.

What bus speed did you test this library at and do you have any idea what might be causing the transfer_in_progress flag to get stuck to true until a new transfer gets it unstuck again?

[vmilea]

Hi!

We're encountering a problem: if we talk to the RP2040 at low speeds (8kHz bus speed) everything is stable but once we increase the bus speed to 100kHz (or 400kHz) we found that the RP2040 can get into a state where slave->transfer_in_progress gets stuck high until a new transfer is started from the bus master.

Are you using external pull-up resistors? The internal ones may be too weak for reliable transmission at high speeds.

What bus speed did you test this library

The bundled examples run at 100kHz, and I remember testing at 400kHz.