I trawled through my archive of this mailing list and found a reference to this:
https://developer.apple.com/library/mac/technotes/tn2274/_index.html It looks like you need to carefully check your descriptors. Stuart On 2/5/15, 12:00 PM, "[email protected]" <[email protected]> wrote: >Date: Thu, 05 Feb 2015 17:31:14 +0100 >From: "Ing. Bernhard Schauer" <[email protected]> >To: [email protected] >Subject: USB Audio Device Class v2: explicit feedback supported? >Message-ID: <[email protected]> >Content-Type: text/plain; charset=utf-8; format=flowed > >Hello @all! > >I currently develop an USB Audio Device according to the version 2 of >the specification and have severe synchronization issues with the >explicit feedback endpoint. As it seems the feedback is never queried by >OS X and so there are clicks in the final audio stream. > >The device supports: > > - 1 Input Terminal with two channels as USB Streaming Terminal > - 1 Clock Source, configurable to 44.1, 48, 96 or 192kHz > - 1 Feature Unit, providing mute and level > - 1 Output Terminal with two channels output as Speaker Terminal Type > >Connection: IT -> FU -> OT >Clocking: IT and OT are clocked by the configurable clock source > >The Input Terminal has two endpoints assigned, one streaming EP and one >feedback Endpoint (both configured as described in the USB DC Spec). > >Basically OS X configures the device to operate under 192kHz and >playback works, but clocks are not perfect and so the buffer within the >device drains until the device mutes the interface. Short afterwards the >buffer is filled again and the device starts playback again. This could >be heared as "click". >To handle that situation the device supports an explicit feedback >endpoint providing the information on how many samples/uFrame in the >fixed point 16.16 format is provided by the device. Interestingly OS X >(10.10) never schedules a transfer on that endpoint and so the Feedback >is never delivered to the OS and naturally the OS does not handle the >need for a little bit more data (0.02%). > >I hope that someone here can point me into the right direction, as the >feedback endpoint works perfectly under Linux and Windows (Thesycon >driver) and I do not have any idea on what could be wrong... > >Thank You, > >Bernhard > _______________________________________________ Do not post admin requests to the list. They will be ignored. Usb mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/usb/archive%40mail-archive.com This email sent to [email protected]
