JC

I am looking into some USB video devices. I found out that some cameras
consume lots of CPU resource (about 60% to 70%). What are possible factors
that might cause this?



The chip we are testing has a stream buffer less then 30 MB/sec isochronous
video transfer. Do you think this might be the reason? From my
understanding, if video stream buffer is small, the driver has to do some
extra process compare to a larger video stream buffer. I am not so sure
about this understanding. Could anyone give me your opinion? What size of
video stream buffer would do you think for a 640 x480 raw data video stream?



Any discuss or suggestion, I would really appreciate.



Julia

Tim Roberts

"JC" <julia_vid@yahoo.com> wrote:
>
>I am looking into some USB video devices. I found out that some cameras
>consume lots of CPU resource (about 60% to 70%). What are possible factors
>that might cause this?

Trying to compress or uncompress the video in the driver can cause this.
Trying to run a high frame rate in a driver that was not well-designed can
cause this. Trying to save a video stream on a slowish disk can cause
this.

>The chip we are testing has a stream buffer less then 30 MB/sec isochronous
>video transfer. Do you think this might be the reason?

30 MB/sec is a lot of data. That's fully half of a USB 2.0 bus, and it's
1/4 of a PCI bus. Many disks are unable to keep up at that rate. That's
the format? Are you decompressing or converting color space?
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.