How to make the camera start capture?

NTDEV
1

Dear Sir,
I rewrite the sample called ISOUSB in DDK. Everything seems to be OK, but I can’t read bytes of data from the ISO pipe.(It is OK to read zero byte of data.) I think the reason for this problem is that the camera hasn’t started capture. As a result, no data exists in the IN ISO EndPoint and I can not read any data.
So my question is how to make the camera start capture?It means what request the driver should send to the device in order to start capture. And how to stop capture is another question.
Thanks for your reading and answering.

2

xxxxx@gmail.com wrote:

Dear Sir,
I rewrite the sample called ISOUSB in DDK. Everything seems to be OK, but I can’t read bytes of data from the ISO pipe.(It is OK to read zero byte of data.) I think the reason for this problem is that the camera hasn’t started capture. As a result, no data exists in the IN ISO EndPoint and I can not read any data.
So my question is how to make the camera start capture?It means what request the driver should send to the device in order to start capture. And how to stop capture is another question

You’re talking about a Video Class device, right?

Generally, you start and stop capture by selecting an alternate setting
for the interface. The default alternate setting allocates no bandwidth
for the isochronous pipe, so no data can flow. By switching to an
alternate setting with bandwidth, data will start flowing.

Have you negotiated the format using the Probe and Commit requests?

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.

3

>You’re talking about a Video Class device, right?
Yes, it is a UVC compliant device.

Have you negotiated the format using the Probe and Commit requests?
Is it necessary to negotiate the format using the Probe and Commit requests?
Is it OK to select the alternate setting directly?

I have read the Probe and Commit Control twice in the UVC white paper and
UVC example. But I haven’t understood them well. Can you explain them with a
simple example?

Thank you!

2007/9/13, Tim Roberts :
>
> xxxxx@gmail.com wrote:
> > Dear Sir,
> > I rewrite the sample called ISOUSB in DDK. Everything seems to be
> OK, but I can’t read bytes of data from the ISO pipe.(It is OK to read zero
> byte of data.) I think the reason for this problem is that the camera hasn’t
> started capture. As a result, no data exists in the IN ISO EndPoint and I
> can not read any data.
> > So my question is how to make the camera start capture?It means what
> request the driver should send to the device in order to start capture. And
> how to stop capture is another question
>
> You’re talking about a Video Class device, right?
>
> Generally, you start and stop capture by selecting an alternate setting
> for the interface. The default alternate setting allocates no bandwidth
> for the isochronous pipe, so no data can flow. By switching to an
> alternate setting with bandwidth, data will start flowing.
>
> Have you negotiated the format using the Probe and Commit requests?
>
> –
> Tim Roberts, xxxxx@probo.com
> Providenza & Boekelheide, Inc.
>
>
> —
> NTDEV is sponsored by OSR
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4

张全煜 wrote:

>Have you negotiated the format using the Probe and Commit requests?
Is it necessary to negotiate the format using the Probe and Commit
requests? Is it OK to select the alternate setting directly?

The alternate setting only selects the bandwidth, not the width, height,
and pixel format. For that, I believe you need the probe and commit
sequence. Otherwise, how will you know what size the images will be?

I have read the Probe and Commit Control twice in the UVC white paper
and UVC example. But I haven’t understood them well. Can you explain
them with a simple example?

Not really. Remember that no one but Microsoft has ever written a UVC
driver for Windows. There are open source UVC drivers for Linux and for
Windows CE that may be able to provide you some hints.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.