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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