Are you talking about isochronous transactions? You could do your reading
from within another thread with a higher priority, but you'll still be
subject to the relatively low priority of the USB workloop. To work around
this there is support for "low latency" isochronous reads and writes which
update the in-memory data structures at hardware interrupt time. See "Using
the Low Latency Isochronous Functions" at
http://developer.apple.com/documentation/DeviceDrivers/Conceptual/USBBook/US
BOverview/chapter_2_section_5.html
--
Steve West (née Hoek) Ph. +64-9-480-2396
Director of R&D Fax. +64-9-480-2397
Serato Audio Research Ltd http://www.serato.com/
> From: Robert Bell <email@hidden>
> Date: Wed, 15 Jun 2005 07:20:17 -0700
> To: <email@hidden>
> Subject: USB missed data issue.
>
>
> Hi all,
>
> This is my first post to this list (perhaps I should not admit
> that). We have a usb device that streams in data from a collection
> device. The problem we are experiencing is that occasionally (during
> very, very high machine load), we notice that some data is missed.
> After searching through the archives of this list, I found a few
> suggestions. The first was that I just load up the bus with read
> requests so that if my app. is not scheduled for a while, there will be
> some reads there to handle the data. The second was that we modify our
> app. to be able to handle lost data.
>
> I have done both of these things. The first solution did indeed
> reduce the lost data samples by about 95%. So our actual loss rate is
> now well below 1% during extremely high load, and 0% during low load. As
> to the second solution ... well it does not crash anymore! :-)
>
> The question I have is the following. Is this the ONLY thing I can
> do? I read that there was pretty much no way of ensuring a higher
> priority for handling usb reads even if I were to lug the whole thing
> into kernel land. Is this true? Or is there some really nasty "I don't
> care about anyone else" option?
>
> Thanks,
>
> Robert.
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