tud_cdc_n_write_flush() blocks if the host isn't pulling data

[OpusElectronics]

Related area

CDC device class, probably others

Hardware specification

RP2040

Is your feature request related to a problem?

Unless I have missed something or not done something correctly, it seems that a call to tud_cdc_n_write_flush() can block if the host is not pulling data. I haven't tried yet, but I'm guessing that it's a more general issue that happens with the vendor device class as well, and possibly others.

Not completely sure how to deal with it gracefully. It's definitely a condition that should be dealt with, and I don't know how to as is.

Describe the solution you'd like

I suppose that the function could have some kind of time-out. If another kind of solution comes to mind to someone else, I'll be also happy to hear it.

If I have missed anything obvious, please let me know and sorry about the request.

I have checked existing issues, dicussion and documentation

• [X] I confirm I have checked existing issues, dicussion and documentation.