USB Audio 2.0 feedback endpoint requirements

Czesław 1

Hi All,

While developing USB Audio 2.0 full speed device I encountered compatibility problem.
Device is implementing speaker with feedback endpoint for synchronization.
To make it work with Windows 10 I followed article https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers?source=docs plus blog that is mentioned in this article.

I do have working device, feedback is used by both Windows 10 and Linux machine the way I expect it to work. Mac however does not work at all with those settings.

I'm inclined to think that the size of feedback data is the issue here.

To make it work on Windows I have max endpoint size set to 4, and data sent on feedback endpoint is also 4 bytes long (even though 4th byte is 0 and is not really needed for 10.14 format per USB specification).
When I tried to specify 3 bytes for feedback endpoint size (as seems reasonable) Windows does not find device usable.

Now the question:
What are requirements for explicit feedback endpoint (size and interval) for Windows USB Audio 2.0 driver?

Thanks
Czesław

Rita Han - MSFT 2,161 Reputation points

2020-09-24T01:56:41.383+00:00

Hello @Czesław , winapi-audio-video tag focus on win32 c++ application development. It seems you are developing drivers, so you can ask a question at MSDN forum: "Windows Hardware WDK and Driver Development" for more professional support. Thanks for your cooperation.
Czesław 1 Reputation point

2020-09-24T06:37:18.183+00:00

@Rita Han - MSFT Thank you for redirection, that was very helpful.
Rita Han - MSFT 2,161 Reputation points

2020-09-24T07:24:41.087+00:00

You're welcome! I'll remove winapi-audio-video tag and set to not-supported since hardware and driver is not supported on this site currently. Thanks for understanding.