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* BIOS or kernel APM bug?
@ 2002-09-23  1:31 James D Strandboge
  2002-09-25 11:51 ` Erik Mouw
  0 siblings, 1 reply; 2+ messages in thread
From: James D Strandboge @ 2002-09-23  1:31 UTC (permalink / raw)
  To: Linux Kernel Mailing List

I recently purchased a usb webcam and found that polling /proc/apm
causes the webcam in xawtv to skip.  I can so this either by doing 'cat
/proc/apm' or using the gnome battstat-applet.  Disabling the
battstat-applet and not touching /proc/apm lets xawtv work fine.

Polling /proc/apm also causes clock drift.

I have a Dell Inspiron 8200 laptop (1.6Ghz Pentium 4).  Using kernel
2.4.18 with rmap12h and preempt-kernel patch.

Jamie Strandboge


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^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: BIOS or kernel APM bug?
  2002-09-23  1:31 BIOS or kernel APM bug? James D Strandboge
@ 2002-09-25 11:51 ` Erik Mouw
  0 siblings, 0 replies; 2+ messages in thread
From: Erik Mouw @ 2002-09-25 11:51 UTC (permalink / raw)
  To: James D Strandboge; +Cc: Linux Kernel Mailing List

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On Sun, Sep 22, 2002 at 09:31:02PM -0400, James D Strandboge wrote:
> I recently purchased a usb webcam and found that polling /proc/apm
> causes the webcam in xawtv to skip.  I can so this either by doing 'cat
> /proc/apm' or using the gnome battstat-applet.  Disabling the
> battstat-applet and not touching /proc/apm lets xawtv work fine.
> 
> Polling /proc/apm also causes clock drift.
> 
> I have a Dell Inspiron 8200 laptop (1.6Ghz Pentium 4).  Using kernel
> 2.4.18 with rmap12h and preempt-kernel patch.

BIOS bug. Reading /proc/apm causes the APM BIOS to switch the CPU to
SMM mode with interrupts disabled so it can slowly poll the battery
about it's status. Result: lost interrupts, dropped frames, dropped
serial characters, clock slowdown. Workaround: don't use a battery
monitor, or don't let it poll every two seconds.


Erik

-- 
J.A.K. (Erik) Mouw
Email: J.A.K.Mouw@its.tudelft.nl
WWW: http://www-ict.its.tudelft.nl/~erik/

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^ permalink raw reply	[flat|nested] 2+ messages in thread

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2002-09-23  1:31 BIOS or kernel APM bug? James D Strandboge
2002-09-25 11:51 ` Erik Mouw

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