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QT Py with TinyUSB HID vs. KVM switch
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QT Py with TinyUSB HID vs. KVM switch

by TheObstacle on Sat Feb 27, 2021 4:27 am

I'm working on a project of building a trackball from scratch. I had been using a Seeeduino XIAO as my controller, and recently switched over to a QT Py SAMD21, as it was an easy drop-in and offered some niceties like pluggable i2c and shiny colored LEDs. :)

As expected, the switch to the QT Py went quite smoothly, but I did find one difference in behavior that's got me puzzled.

I have a couple of computers on a KVM switch. When I switch between them with the trackball connected, the XIAO handles the switch correctly, but the QT Py sometimes stops getting HID reports to the host after switching. I've determined that the code on the trackball is still running (in fact, it doesn't even seem to reset when I switch KVM inputs), the host just doesn't see any HID reports after the switch.

Both the XIAO and the QT Py are running exactly the same Arduino code (I'm building to them both from the same project in VS Code/platform.io), and as far as I can tell are using the same TinyUSB library and other source. From a programming perspective the chips seem almost identical, but I assume there must be some differences either in hardware or possibly at the bootloader level? (Is that even involved in handling USB endpoints?)

The code for the project is here: https://github.com/monroewilliams/trackball

Thanks,
-- monroe
TheObstacle
 
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Joined: Fri Jan 17, 2014 9:55 pm

Please be positive and constructive with your questions and comments.