[mythtv-users] OT: System clock running very slow

[Nick Rout]

On Tue, Jan 19, 2010 at 1:11 PM, Ronald Frazier <ron at ronfrazier.net> wrote:
>> Anyone have any ideas as to what is causing the clock to slow so much. I may
>> have done package updates which could have caused this. Anyone else having a
>> similar problem?
>
> Could the battery on your motherboard be dying? Although I would only
> expect the battery to be necessary while power is off, I've heard of
> cases where it slows the clock even while the system is running.
> Whether or not that's true or not I can't say (I've never actually had
> a motherboard battery die on me).
>
> I don't know if the bios screen gives you a way to check the voltage,
> but if not you can pull it out and test the voltage with a multimeter
> (just be warned that doing so will probably cause you to lose your
> bios settings). Alternatively, if it's possible to shut your system
> down for a length of time, you could see if the skew only happens when
> running (if so, I think that would eliminate the possibility of the
> battery being the issue). For example, by your report it should lose
> about 3 to 4 minutes every hour it's running. So, reboot and go into
> the bios screen. Synchronize the bios clock it with a reliable watch,
> power it off for an hour, then power it on and go back to the bios,
> and see how much skew there was.
>

Just thinking about this some more, I assume this time is being lost
while the system is running. If so, the kernel is keeping track of the
time (subject to being adjusted by ntpd or ntpdate). The bios/hardware
clock is irrelevant while the system is running, it only supplies the
time to the kernel at bootup. This much I know for sure.

The kernel keeps track of the time by counting the system timer
interrupt. Where this interrupt comes from I am not sure, but I assume
it must be hardware based on the motherboard, at least on an
i386/amd64 system.

So there is likely a motherboard problem, which indeed may be caused
by the interrupt timer, which may be caused by the battery.