Polling /proc/apm causes usb hiccups and clock drift

Polling /proc/apm causes usb hiccups and clock drift

[James D Strandboge]

I recently purchased a usb webcam and found that polling /proc/apm
causes the webcam in xawtv to skip.  I can do this either by doing 'cat
/proc/apm' or using the gnome battstat-applet.  Syslog says:

Sep 23 10:14:17 sirius kernel: usb-uhci.c: iso_find_start: gap in
seamless isochronous scheduling
Sep 23 10:14:18 sirius kernel: quickcam: too little data by 48260
Sep 23 10:14:18 sirius kernel: quickcam: failed qc_imag_convert()=-90


Disabling the battstat-applet and not touching /proc/apm lets xawtv work
fine without the above errors.  Polling /proc/apm also causes clock
drift.

I have a Dell Inspiron 8200 laptop (1.6Ghz Pentium 4).  Using kernel
2.4.18-686 from debian.  I read that this happened to people in the 2.2
series.  Is this a kernel apm bug or BIOS problem?  Do I just have to
live with it?

Thanks,

Jamie Strandboge

-- 
Email:        jstrand1@rochester.rr.com
GPG/PGP ID:   26384A3A
Fingerprint:  D9FF DF4A 2D46 A353 A289  E8F5 AA75 DCBE 2638 4A3A

Re: Polling /proc/apm causes usb hiccups and clock drift

[James D Strandboge]

On Tue, 2002-09-24 at 12:22, Philipp Matthias Hahn wrote:
> Hi James!
> 
> On Tue, Sep 24, 2002 at 09:12:00AM -0400, James D Strandboge wrote:
> > Disabling the battstat-applet and not touching /proc/apm lets xawtv work
> > fine without the above errors.  Polling /proc/apm also causes clock
> > drift.
> > 
> > I have a Dell Inspiron 8200 laptop (1.6Ghz Pentium 4).  Using kernel
> > 2.4.18-686 from debian.  I read that this happened to people in the 2.2
> > series.  Is this a kernel apm bug or BIOS problem?  Do I just have to
> > live with it?
> 
> This is a known BIOS limitation. Interrupts are disabled during
> APM-BIOS calls and they may take a long time, during which the kernel
> might miss some clock interrupts.
> You can try to enable CONFIG_APM_ALLOW_INTS=y during kernel compile, but
> your BIOS might not like it.
> 
Thanks.  Yes I have this disabled because it has caused problems with
others using the inspiron 8200.  I will play with it though.  This most
definitely is a BIOS bug then, and I have to live with it.  Is ACPI any
better?

Jamie Strandboge

-- 
Email:        jstrand1@rochester.rr.com
GPG/PGP ID:   26384A3A
Fingerprint:  D9FF DF4A 2D46 A353 A289  E8F5 AA75 DCBE 2638 4A3A

Re: Polling /proc/apm causes usb hiccups and clock drift

[Thomas Hood]

James D Strandboge <jstrand1@rochester.rr.com> wrote:
> polling /proc/apm causes the webcam in xawtv to skip.
> [...]
> Is this a kernel apm bug or BIOS problem?

The apm driver calls the APM BIOS with interrupts disabled
each time /proc/apm is read.  This appears to be taking
too much time away from video processing.




__________________________________________________
Do You Yahoo!?
Everything you'll ever need on one web page
from News and Sport to Email and Music Charts
http://uk.my.yahoo.com