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embassy-rs / embassy

Modern embedded framework, using Rust and async.
https://embassy.dev
Apache License 2.0
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STM32F4: USB HID Keyboard not working in BIOS (before Linux start) #2997

Open dariogoetz opened 1 month ago

dariogoetz commented 1 month ago

MCU: STM32F401CC

I have written an embassy-based keyboard firmware for a keyboard. The firmware works well in Linux. However, the keyboard does not produce anything when the laptop asks for a system password when booting (before Linux starts).

I could reproduce the issue with the code from the examples directory examples/stm32f4/src/bin/usb_hid_keyboard.rs (adjusted for clocks of the STM32F401CC, otherwise vanilla): Within my Linux system, it produces an a when pulling PC13 up. In the password prompt before starting Linux, however, nothing happens.

I have another firmware based on rtic, stm32f4xx-hal, and usb-device that does not have this issue, so I would exclude it being a hardware issue.

Any ideas, what the issue could be?

joelsa commented 1 week ago

Any ideas, what the issue could be?

If the device implements the boot protocol, the device subclass needs to be set to 0x01, see page 8 of the USB HID specification: https://www.usb.org/sites/default/files/documents/hid1_11.pdf

So as a bare minimum, this line here needs to be set to 0x01:

https://github.com/embassy-rs/embassy/blob/26e660722cca9151e5a9331c328421145509ab20/examples/stm32f4/src/bin/usb_hid_keyboard.rs#L77C12-L77C28

Of course, this should only be set to 0x01 if your device supports the boot protocol. See Appendix F and G of above document for information on what's needed to implement it.

Depending on the rest of your Code chances are, that you do not need to do anything apart from changing the referenced line with the subClass, so you might try that out.