[ntp:questions] What level of timesynch error is typical onWinXP?
David Woolley
david at ex.djwhome.demon.invalid
Wed Nov 3 22:08:41 UTC 2010
David L. Mills wrote:
> I don't think that is right. The adjtime() call can be in principle
> anything, accoridng to the Solaris and FreeBSD man pages, but the rate
> of adjustment is fixed at 500 PPM in the Unix implementation. If the
> Linux argument is limited to 500 microseconds, Linux is essentially
> unusable with NTP. I would be surprised if this were the case.
I think what he is really saying is that he is not using the kernel
discipline and ntpd is tweaking the clock every second, but he has
broken hardware, which requires a correction of more than 500ppm, and,
as he is describing it, adjtime has a residual correction to apply
before the next tweak, or more likely ntpd is limiting it to 500ppm.
As to Linux, I would guess most users of ntpd are using Linux.
Miroslav: ntpd requires an uncorrected clock that is good to
significantly better than 500ppm. You can probably get away with
450ppm, but the transient response will be compromised.
A good quality PC should be within about 10ppm. A cheap one should be
within about 50ppm. > 500ppm is broken. You can use tickadj to
compensate in steps of 100ppm, but a machine with that error is likely
to have other problems; the crystal may be barely disciplining the
oscillator.
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