STM32F4 HAL USB CDC - Occasional re-enumeration when I2C is also enabled

[mwp]

This is a super super weird one.

My device (STM32F401RC) uses the latest HAL libs vs STM32CubeIDE. USB is configured as device-only, CDC.

It works *perfectly* until i also enable one of the I2C peripherals (HAL, config'ed as I2C slave) and send/recv I2C data.

When i do so the OS (happens with Win10/11, Linux and OS-X) occasionally (every 5-20 sec) drops and re-connects the USB connection to my device.

What's stranger again, it'll only happen when connected via a USB hub. When connected directly to the PC it works ok.

I've also tried different hubs, it happens with all of them.

I've also tried connecting my device though a Total Phase USB analyzer. When its connected to the analyzer and the hub, the error no longer occurs (sigh).

Any ideas??

Thanks in advance!

[waclawek.jan]

Sounds more like hardware issue to me, i.e. I'd investigate power source/drop, crosstalk between I2C and the USB lines, observe using oscilloscope USB lines maybe even unconnected (maybe loaded by a 15k pulldown mimicking the hub) with and without I2C.

JW