C++/VB - usb bulk transfer question
Asked By cpparm
03-Jul-07 08:46 PM
the maximum packet size of the pipes on my usb device is 512 but it seems
like with WDF I don't need to send seperate request. I just call
WdfUsbTargetPipeFormatRequestForWrite/Read followed by WdfRequestSend in my
code. It seems to work no matter how big my buffer is. Does the framework
take care of dividing the buffer up? I sometimes need to read a data buffer
as big as 10M, is there any problem sending a 10M buffer in FileRead and
just forward the request in my kernel driver?
WdfUsbTargetPipeFormatRequestForWrite
(1)
Vista
(1)
XP
(1)
WdfRequestSend
(1)
FileRead
(1)
Boekelheide
(1)
Providenza
(1)
Segement
(1)
Doron Holan [MSFT] replied...
the framework does not segement the buffer it max packet sizes, the usb core
does that. do not confuse max packet size with max transfer size. just
send the transfer in one chunk and the lower layers will take care of the
segmenting for you
d
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Tim Roberts replied...
Right. You didn't you need to do so with WDM either.
No. The host controller takes care of this. It has always done so.
http://support.microsoft.com/kb/832430
For USB 2.0 devices, Microsoft documents a 3.3MB limit.
--
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.
Wei Wang replied...
Thanks a lot for the answer. I was confused.
Does this 3.3MB limit exist in Vista also?
Tim Roberts replied...
I do not know, but it does not really matter. As a practical matter, you
cannot really ignore XP.
--
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.
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