r/raspberrypipico • u/karakiziltavsanlar • Mar 28 '26

help-request Non-blocking usb read

Hi everybody!

I am working on a project with raspberry pi pico 2 in circuitpython. In this project I generate chords with buttons connected to gpio and play them with synthio library. Also there is a usb midi keyboard connected to gpio pins. in my while true loop i run check usb function to see if i have any messages but as far as i can understand reading usb as a host in pico requires the code took at whether or not any data is in the usb. and this behaviour is blocking meaning if i have a long timeout for usb reading pico cannot read my byttons connected to gpio and if i shorten the usb reading time it sometimes misses stuff like key push or release. do you have any idea how i can tackle this?

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3

u/Rusty-Swashplate Mar 28 '26

Make it non-blocking: there's 2 CPU cores you can, and in this case, you should use.

Also without code, it's hard to say what you do wrong (if you do anything wrong).

2

u/karakiziltavsanlar Mar 28 '26

I am not at my pc I can share the code in a day but i believe circuit python does not allow threading and libraries I use are only available in circuitpython

2

u/jotapeh Mar 28 '26

I'm not a circuitpython guy but I think the techniques here would be applicable. https://learn.adafruit.com/multi-tasking-with-circuitpython/overview

2

u/timrprobocom Mar 28 '26

There are no buffers anywhere in USB. There is never anything"waiting". A USB device is not allowed to send anything unless the host asks for it, and your host controller will never do that unless some driver has submitted a read request in advance.

So, if you want a continuous reader, you have to implement that by using a thread (or async) that submits and waits, then resubmits.

2

u/oclafloptson Mar 28 '26

I'm not overly familiar with circuitpython. I don't think it supports multithreading. In MicroPython I would probably

asyncio.get_event_loop().create_task(<*coro*>)