Re: USB High-Speed uFrame Limitations
Re: USB High-Speed uFrame Limitations
- Subject: Re: USB High-Speed uFrame Limitations
- From: Mark Moore <email@hidden>
- Date: Tue, 13 Nov 2012 08:22:29 +0100
Hi Alison,
Thanks for the feedback.
The only documentation that I could find refers to a limit of 1024 bytes per microframe with HS (http://developer.apple.com/library/mac/#technotes/tn2274/_index.html). Is this documentation now obsolete - it was updated only a year ago?
The same document also suggests customising the AppleUSBAudio driver, yet the source appears to be unavailable. Was the withdrawal of the source code a policy change or simply an oversight that might be corrected?
[Some context, I have a client with a USB audio interface with a very large number of channels, and which exceeds the 1024 byte per uFrame limitation. It currently does not work with OSX, though I do not have details of the precise failure mode at present.]
Many thanks,
-- Mark
On 13 Nov 2012, at 01:28, Alison Hughes <email@hidden> wrote:
> 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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