How to move a CPU out of C3 in USB WebCam Driver

NTDEV
1

I encountered a strange problem that in some Vista NoteBook Computers, When Our USB WebCam driver is previewing, the CPU will soon enter C3, and never come back to C0; it will cause the preview lagged. I would like to know if there is a simple way in my USB AVStream driver to move a CPU out of C3?

2

This is not really my thing, but, as it is late and you might not hear
until tomorrow, you might want to look at PoSetSystemState() and
PoRegisterSystemState() in the WDK.

Good luck,

mm

adroit@ms4.hinet.net wrote:

I encountered a strange problem that in some Vista NoteBook Computers, When Our USB WebCam driver is previewing, the CPU will soon enter C3, and never come back to C0; it will cause the preview lagged. I would like to know if there is a simple way in my USB AVStream driver to move a CPU out of C3?

3

Dear mm,

Got it. Thanks a lot. I will give it a try.

Best Regards,

Kevin

4

No problem. I hope it works for you.

Good luck,

mm
adroit@ms4.hinet.net wrote:

Dear mm,

Got it. Thanks a lot. I will give it a try.

Best Regards,

Kevin

5

Dear mm,

I gave it a try, but it won’t work. Thanks anyway. Any new suggestions?

Kevin

6

The CPU enters C3 when there is no activity - no threads to run and no interrupts happening. If your webcame device were to generate interrupts, it would bring the CPU back out of C3 and execute properly. Or, if your driver had a thread scheduled to run, you’d get it run. Can you explain a little more fully how C3 is causing your problem?

Dave

7

Dear Dave,
The problem is the preview image will be lagged; about 0.2 frame per second. These notebooks are equipped with Vista OS, and even Microsoft UVC inbox driver has the identical problem. I also tried another company’s UVC camera, and they are all the same. The preview program I use is amcap.exe, but if I use amcap2 resided in WDK 6000, no problem will occur; 30 frame per second.