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Date:      Thu, 5 May 2005 10:20:51 +0200
From:      Anthony Atkielski <atkielski.anthony@wanadoo.fr>
To:        freebsd-questions@freebsd.org
Subject:   Re: Clock running fast
Message-ID:  <1117006021.20050505102051@wanadoo.fr>
In-Reply-To: <20050504210519.GA51317@angel.falsifian.afraid.org>
References:  <42792740.3040501@houston.rr.com> <5.1.0.14.2.20050504154906.4311e370@209.152.117.178> <20050504210519.GA51317@angel.falsifian.afraid.org>

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James Alexander Cook writes:

> I might be wrong here, but doesn't NTP only make occasional adjustments to the
> system clock?

It tries to slew the clock as smoothly as possible to bring it into
alignment with the correct time.  It does not make sudden large changes
to the clock.

> If your clock runs twice as fast as normal, it would jump to the correct time
> every time ntpd corrected it, but in between automatic adjustments, the time
> would become wildly innacurate.

If your clock is that far off, it would be difficult for NTP (or
anything else) to correct it often enough to keep it running smoothly
with the correct time.  You're talking about an accuracy of 50%, whereas
even bad PC real-time clocks usually have an accuracy of better than
99.9%.

If NTP sees that it cannot discipline the clock successfully, it will
say so and give up, IIRC.

The real mystery is why the clock is running so fast.

> Also, wouldn't a problem like this make your system try to play movies at
> twice the frame rate, and things like that?  NTP is worth a try, but I doubt
> if it will fix things like that.

I don't think the real-time clock comes into play for multimedia work,
but I might be wrong.

-- 
Anthony




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