Synchronous or adaptative USB audio

[nleroy]

Hi all,

I am using USB slicekit with an audio slice to develop a USB audio device. The system works very well when connected to a Mac/PC that plays files since the XMOS clock is used in asynchronous mode.
However for a particular application, I would like that the XMOS device uses an adaptative clock mode : the device must synchronise to the host clock.
It seems that the code template that I used to develop my code is only asynchronous (the code is app_usb_skc_u16).
Is there a way to turn that code into adaptative or synchronous mode ? I can't find anything about that in the code.
Or is there a code example for those modes ?

Thanks for your help,
Nicolas

[Ross]

Synchronous should be a relatively trial modification to the descriptors. You will then need to drive an external clock multiplier/VCXO or similar to generate the audio master-clock based on SOF's from the host (I've used CS2100 in the past)

I've never implemented adaptive in an xcore - but a similar scheme.

[Ross]

Oh, you could also offer a mode that is synced to the PC but still runs in Async mode, this is sort of forbidden in the USB spec but will work. It also means you can change modes "on the fly"

[nleroy]

Hi thanks for your answer.
I will try to figure out how to get a clock from SOF as you said.
Regards

[Ross]

I did the descriptor work a while back.. descriptors file attached. Changes are guarded by USB_SYNC_MODE_SYNC. Let us know how you get on...

Cheers