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So I have this issue with an USB to serial converter. On a fresh booted device it shows up as /dev/ttyUSB0 and I can connect to the serial device with minicom -D /dev/ttyUSB0.

However, after some time (this could be minutes or hours, haven't figured out any trigger), the flow of data just stops. If I close minicom and try to start it again, I get the error minicom: cannot open /dev/ttyUSB0: No such file or directory. The device doesn't even show up in lsusb anymore. Unplugging / re-plugging doesn't help. I also re-soldered all the solder pads on the adapter to avoid connectivity issues but it didn't fix the issue.

The only thing that fixes the issue is to reboot my computer. Which is maximum inconvenience in most cases because I have to close and re-open all the programs I'm working in.

Any ideas what's happening here and how to fix it without closing all my open programs?

Computer hardware is a ThinkPad T14 (first gen) with AMD processor. OS is Ubuntu 21.04.

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1 Answer 1

Reset to default
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You should probably compare the last lines of dmesg before and after the device disappeared. You'll probably read that the USB resets due to the device or host controller malfunctioning.

There's different things that could be going wrong here: for example, a fault in the device connected (maybe you're powering some embedded device using the same USB 5V?) might be drawing too much current, leading the USB port to trigger short circuit protection and turn itself off until reset. The USB host controller might simply have bug, and hang. (It wouldn't be the first time a lenovo Laptop ships with firmware bugs.)

USB-to-serial converters are often very cheaply made – including counterfeit ICs that misbehave.

So, make sure you're

  • not having any hardware fault in whatever is connected to your USB to serial converter
  • your USB to serial converter is reliable - at the prices of these, it might be wise to simply try another model.
  • you've got your device firmware updated (sudo fwupdmgr refresh; sudo fwupdmgr get-updates; sudo fwupdmgr update)
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