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Re: Core audio driver


On Feb 17, 2005, at 9:17 PM, Mark Cookson wrote:

Be careful in your terminology here.  There is NO USB Audio 2.0 Device specification (that’s released to the public).  There is only a USB Audio 1.0 Device specification.  There is of course USB 2.0, and you can put USB Audio 1.0 Device functionality on a device that connects to the host over USB 2.0 and runs at high speed, but that doesn’t make it a USB Audio 2.0 device, and you will find a couple of short comings in the USB Audio 1.0 Device specification that limit the device’s usefulness.

The problem that you are seeing is that there is a bug in the USB stack that prevents the USB Audio 1.0 driver from working correctly on the USB 2.0 stack.  Until that is fixed, there is nothing that the driver can do to talk to a USB 2.0 device.

Could you please elaborate on this point? I'm currently working on a project that involves the connection of an audio/midi external USB 2.0 device (high speed needed). Until now, our plan was to rely on the generic Mac OS X audio and midi drivers. IIRC this could be not possible and we may have to develop our own driver :(

Thanks

You must run your device with at least two endpoints and therefore must run the video and data in parallel because the USB Audio 1.0 Device specification doesn’t allow for video to be interspersed within the audio stream.  You will need to synchronize the two streams internal to your device so that they arrive at the host at the same time (that the audio frame for the video frame arrives in the same USB frame as the video frame’s data).

Good luck,
Mark
--
Mark Cookson
M-Audio, a division of Avid
225 Locust St.
Hudson, WI 54016



Philippe
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