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From: Jack DarkStar on 17 Mar 2010 04:23
I have a bulk usb device and the PC requests the status of the device
polling a usb bulk pipe. Using Windows XP Service pack 2, the time of the
status request (write request+read status) is less then 40mS.
After installing service pack 3, the time of the status request could
increase up to 600mS.
I suspect that service pack 3 applied some patch to obtain this behaviour.
Can i increase the priority of usb transfers or change the configuration of
Windows to obtain the same behaviour of Service pack 2?
I tried to call SetThreadPriority with THREAD_PRIORITY_TIME_CRITICAL, but
this doesn't reduce the time of the status request.
Best Regards





From: Tim Roberts on 18 Mar 2010 23:37
"Jack DarkStar" <gzanone(a)emmedi.com> wrote:
>
>I have a bulk usb device and the PC requests the status of the device
>polling a usb bulk pipe. Using Windows XP Service pack 2, the time of the
>status request (write request+read status) is less then 40mS.
>After installing service pack 3, the time of the status request could
>increase up to 600mS.
>I suspect that service pack 3 applied some patch to obtain this behaviour.

There should not have been any changes that would cause this kind of thing.
A USB write followed by a USB read should take only a few milliseconds. How
are you doing the polling? Do you have a read request on permanent standby
using overlapped I/O?

I would point out that, with a control request, you can do a write and a
read in a single transaction.
--
Tim Roberts, timr(a)probo.com
Providenza & Boekelheide, Inc.
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