RP2040: USB Serial connection sometimes lost

[timonsku]

I have a hard time reproducing this but I get occasional drop outs for the REPL that are only recoverable after resetting the Pico.
Most of the times this would happen after a code change but also happened just while printing values to the console. It seems to have started to appear after I added the pwmout module but can't say for certain as I haven't extensively used the REPL either before adding that module.
The MSD is working fine after the bug occurs and code changes are still being applied after the serial connection died. Closing the connection and re-opening does not work, I have to fully reset the chip to be able to see the REPL again.

This is under Windows 10, running CPY nightly en_US-20210209-5ba28e9 and using Putty as the serial terminal.

[dhalbert]

Are you using pin GP15? There is a fix needed when using that pin that can interfere with USB in various ways. Try the "Absolute Newest" build from the board page in circuitpython.org.

[timonsku]

I avoided using that pin.
I was running the build from 3 commits ago, it doesn't seem the last two commits touched anything relevant.
To be clear, USB is not dying, only the REPL.

[dhalbert]

Thanks for the feedback. We'll leave this open, and if you figure out a reproducible case, of course let us know. We recently improved the way we are servicing USB interrupts but there could still be an issue.

[jerryneedell]

I have been seeing something similar as well.
It seems to happen more frequently when I had a button attached to the RUN pin, but it has also occurred with it removed.
I am able to simply reconnect to the REPL. No reset necessary.

[timonsku]

What OS are you using @jerryneedell ?

[jerryneedell]

Linux Ubuntu 20.04

[timonsku]

Ok that makes sense, I'm pretty sure the need for a reset is a Windows specific issue. Its very easy on Windows to get a COM port into a zombie state where no application can claim it any more unless its removed. I have never seen that on Linux.

[jerryneedell]

I've also a seen it on a Raspberry Pi.

[jerryneedell]

FWIW -- on the Raspberry Pi, I have MicroPython on the Pico and I also see occasional spontaneous resets of the board.

[hathach]

this could be related to hathach/tinyusb#655 , may be worth doing tinyusb update. rp2040 port is still early.