USB HID, OS X and APP_USBD_HID_USER_EVT_IN_REPORT_DONE bug or unexpected behaviour

[Oleh Hordiichuk]

Hello,

our application requires to emulate keyboard, e.g. to write strings like "hello world\n" as it might be typed by the keyboard. According to the recommendations in this topic:

devzone.nordicsemi.com/.../writing-words-to-usb-composite-keyboard-in-usbd_hid_composite

we implemented nrf_queue of keyboard codes & modifiers:

app_usbd_hid_kbd_codes_t
app_usbd_hid_kbd_modifier_t

For example to encode char "A", it pushes to the queue the following codes & modifiers:

1) press "Shift"

2) press "A"

3) release "A"

4) release "Shift"

We send 1 code\modifier at once and then wait for APP_USBD_HID_USER_EVT_IN_REPORT_DONE. Right after we receive this event, we send the next code or modifier.

This works perfectly on Windows and Linux. However on Mac OS the behaviour is absolutely different. When we plug the device via USB, we constantly receive APP_USBD_HID_USER_EVT_IN_REPORT_DONE, however no real data being sent through HID key_control\modifier_set_state functions. Once we try to send smth, these events either disappears at all or randomly generated\not generated. We assume it should be a bug or the API is not working as expected.

Additional question: does our type of application should wait for APP_USBD_HID_USER_EVT_IN_REPORT_DONE for both

app_usbd_hid_kbd_key_control
app_usbd_hid_kbd_modifier_state_set

or only for key_control functions?

[Joakim Jakobsen]

Hi.

Could you add which version of the nRF5 SDK you are working with? Also what device, softdevice, Mac OS version etc.

Br,
Joakim

[Oleh Hordiichuk]

Yes, sure. Sorry I forgot to mention it:

1) The device is based on nrf52840 

2) Softdevice S140, nrf5 SDK v17.0.2

3) Mac OS Big Sur 11.1

Also here is an update on this topic. 

A possible semi-working workaround here (for those who encountering same issue): 

it's possible to send reports from timer, e.g. every twenty ms. In this case it's possible to write strings on mac os. However, it's still is not a reliable method and from time to time app_usbd_hid_kbd_modifier_state_set\app_usbd_hid_kbd_key_control will return NRF_ERROR_BUSY and sometimes characters might be lost. Increasing the timeout value to 50 or 100 ms will decrease probability of these errors & therefore increases reliability. However, of course this is not a normal way it should be done. 

[Joakim Jakobsen]

Thanks for the additional information.

I'll do some tests on the example on Mac OS and get back to you.

Br,
Joakim