> > It seems such a feedback endpoint is now required by the standard:
> > "The USB 2.0 specification states that if isochronous OUT data
> > endpoint uses the asynchronous synchronization, an isochronous
> > feedback endpoint is needed."
> We actually have both EP IN and EP OUT on the UAC2 function:
>     272:static struct usb_endpoint_descriptor fs_epout_desc = {
>     282:static struct usb_endpoint_descriptor hs_epout_desc = {
>     349:static struct usb_endpoint_descriptor fs_epin_desc = {
>     359:static struct usb_endpoint_descriptor hs_epin_desc = {

Yes, but that isn't the issue AFAIU ? In the USB 2.0 standard related to 
synchronization (http://sdphca.ucsd.edu/lab_equip_manuals/usb_20.pdf chapter 
5.12.4), an isochronous OUT ep with asynchronous synchronization is *required* 
(at least by Microsoft) to have a feedback IN ep, to be able to report to the 
host the rate so no under- or overrun condition occurs.



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