NRF_USB->EVENTS_EPDATA fails to trigger

[James Devine]

Hiya!

I am writing code to add support for USB on the NRF58233/58240 to MakeCode. MakeCode relies upon WebUSB. At any point, a user can close the website which causes the web usb stack to stop reading from the device. When this happens, the synchronous code I've written hangs indefinitely.

I have added a software timeout that causes the NRF to exit the while loop and resume application operation until it gets an out transaction from the host. The timeout however is too short on some occasions and times out prematurely.

Instead of increasing the timeout, is there a more elegant way to detect that the host is no longer reading a transaction? Isn't it weird that the EPDATA event is not triggered?

I attach a reference to the code:

codal-nrf52/NRF52USB.cpp at master · lancaster-university/codal-nrf52 (github.com)

and a screenshot from my usb analyser with the timeout in the above code removed:

After line 5471, the MCU has entered the while loop on EVENTS_EPDATA which it never exits. I am at this time using an NRF52833 DK (PCA10100 v0.7.0) and a NRF52840-DK (PCA10056 v2.0.1). The issue is present on both DKs.

Happy to share binaries as required... 

[Marjeris Romero]

Hi again,

USBD automatically detects lack of activity on the USB bus for more than a defined amount of time. When no activity has been detected for longer than tUSB,SUSPEND, USBD generates the USBEVENT event with SUSPEND bit set in register EVENTCAUSE.

So in your case it makes more sense to check if this SUSPEND bit is set or not in the device as no data is being transferred when the web browser is closed.

Our developers also pointed out that developing a own USB stack is very time-consuming, and some parts of the USB protocol are best to do in a non-synchronous fashion, so they strongly recommend using the Zephy USB device stack as a based for interfacing with webUSB: https://docs.zephyrproject.org/latest/reference/usb/index.html

Best regards,

Marjeris