Unable to use HID keyboard in boot OS (macOS boot screen)

[bmosley]

I started putting together a project with my Trinket M0 to use for switching boot volumes on macOS. My goal was to have it select a volume by keystrokes. However, it doesn't seem to be working.Working correctly in macOS once booted

Using the same code for HID keyboard:

1. plug trinket m0 into usb on mac
2. reboot system

import time

import board
import digitalio
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS
from adafruit_hid.keycode import Keycode

# The keyboard object!
time.sleep(1)  # Sleep for a bit to avoid a race condition on some systems
keyboard = Keyboard()
keyboard_layout = KeyboardLayoutUS(keyboard)

while True:
    keyboard.press(Keycode.LEFT_ALT)
    time.sleep(40)
    led.value = False
    keyboard.release_all()

[dhalbert]

The HID keyboard currently presented by CircuitPython is not a boot device keyboard, with its own endpoint(s), which is what the Mac Open Firmware ("BIOS") and regular PC BIOSes expect. It's part of a composite HID device that includes mouse, multimedia keys, and a gamepad. This was to save endpoints for other purposes.

We've had one other person who wants a boot-compatible keyboard and we're thinking about that - we have to count up the available endpoints and what we want for the future (e.g. USB MIDI). Also, in the long run, we are thinking about how to provide user-configurable HID devices.

[bmosley]

Thanks. I completely understand and figured that this wasn’t currently supported but thought filing a bug was the best way to ask/suggest implementation of the feature. Is there any roadmap for future HID support? And MIDI sounds quite awesome too :)

[dhalbert]

No specific timeline with dates, but your request is noted and it's a vote!

[bmosley]

wonderful, thank you!

[ATMakersBill]

This is marked as closed - was it done? If the fix was the same that I used in the XBox stuff which requires a custom build, is there any example of making this work?

[dhalbert]

The fix requires a new descriptor and its own endpoint, at least. I'm not sure what else. Perhaps it could be added as a compile option for the descriptor generating Python script, and then later as a boot.py. We can reopen this as long term.

[ATMakersBill]

I understand this not being in the core CP, but I do think it should remain open until there's some way to do it. I don't mind having to do a custom build (like we do for the XBox Adaptive Controller), but we have found lots of folks who really want to use devices through KVMs, and the composite devices don't work through them.
Here's our current pressing issue: https://www.facebook.com/groups/ATMakers/permalink/815702142174560/

[ATMakersBill]

BTW, thanks Dan

[dhalbert]

Do you need a bootmode mouse HID capability too?

[ATMakersBill]

Um... I don't think so? I think the reason this is needed is that the KVM listens in on the keyboard commands and relays them. That lets it watch for trigger keystrokes ('scroll-scroll-enter') to jump between devices. We don't kneed the triggers, but the stupid KVM doesn't know what to do with composite devices. It might be that we just need a non-composite device w/no other profiles. Or only a single device (no serial/mass storage?)

I just know it is a known issue that "complicated" keyboards (even those with media keys) don't work.

[bitboy85]

Here is another vote for it :)
By now i've tried arduino, vusb, teensy, and pico pi and only teensy seems to have a full featured keyboard that works in BIOS and KVM devices.
@ATMakersBill
The teensy itself is also a composite device, having keyboard, mouse, gamepad, serial and still works fine with a KVM. So my best guess is, that it only depends on a correct implementation of the boot keyboard.
@dhalbert
As far as i know, a boot keyboard needs its own descriptor and endpoint and on top of it, it has two additional functions which are described in the usb docs.

[dhalbert]

We are currently out of endpoints on most boards with 8 endpoints, having added a second CDC. If someone would like to contribute boot keyboard and mouse descriptors and compile flags, we'd be happy to include them. We would not turn them on normally, since they would remove having MIDI or the second CDC available by default.

This is another indicator for user-configurable USB and USB HID descriptors. However, we are pretty much out of space on the smallest builds, and don't have room to add the code for this. It would have to be on something other than the non-Express SAMD21's.