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From: Erik Mouw <>
To: James D Strandboge <>
Cc: Linux Kernel Mailing List <>
Subject: Re: BIOS or kernel APM bug?
Date: Wed, 25 Sep 2002 13:51:03 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <1032744662.6912.69.camel@sirius.strandboge.cxm>

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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.


J.A.K. (Erik) Mouw

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      reply	other threads:[~2002-09-25 11:45 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-09-23  1:31 James D Strandboge
2002-09-25 11:51 ` Erik Mouw [this message]

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