Hello All,
We are testing a USB Audio device on a new Mac-Mini with the
most recent OS. We are having trouble with the synchronization /
explicit feedback channel, in that the operating system never actually makes use
of our feedback channel. So we have 2 questions:
1) Does the Apple USB Audio class driver support
Explicit feedback channel as defined in USB Device Class Definition 4.6.2.1?
2) If it does, is there anything special we need to do
to convince the class driver that it should be used?
A little bit about the device topology:
Endpoint1: Is an audio
output endpoint that is Asynchronous,
Isochronous. bSynchAddress is set to 0x3 to signify
endpoint 3 is the synchronization endpoint.
Endpoint3: Is a “4.6.2.1
Standard AS Isochronous Synch Endpoint Descriptor”. It
provides details on how much more / less data we need to synchronize our data
with the host.
Right now, the Audio Class Driver ignores Endpoint3
completely, and as a result a mismatch in clock frequencies between the host
and the audio device eventually cause buffer drift and we lose synch. The
same device works fine on other operating systems. It just doesn’t seem
to work on this mac-mini. We never get a token to be able to send
data up Endpoint3.
Any ideas?
Thanks,
James