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Re: USB High-Speed uFrame Limitations
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Re: USB High-Speed uFrame Limitations


  • Subject: Re: USB High-Speed uFrame Limitations
  • From: Alison Hughes <email@hidden>
  • Date: Mon, 12 Nov 2012 16:28:09 -0800

Mark,

AppleUSBAudio is designed to support multiple transactions per microframe as described by the USB 2.0 Specification Section 5.9.2 "High Bandwidth Isochronous Endpoints".  However, we have yet to see a class compliant USB Audio device which supports this feature so it remains untested.  I'd like to complete this testing before updating the documentation.

Thanks,
Alison

On Nov 8, 2012, at 3:22 AM, Mark Moore <email@hidden> wrote:

> Can anyone confirm if the documented limit of one 1024 byte transaction per USB2 high-speed uframe still exists in the current 10.8 AppleUSBAudio driver?
>
> From what I can tell from older versions of the source code there are some assumptions made that there can only be one transfer per uFrame. However, these look like historical carry-overs from the original full-speed design rather than a fundamental issue with the driver. Comments on the USB lists and inspection of the source code suggests that there is no corresponding limit in the USB UIM.
>
> Also, can anyone comment on the availability of the AppleUSBAudio.kext source code?  It seems to be missing from all the archives and developer downloads at Apple at the moment.
>
> Thanks,
>
> -- Mark
>
>
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