Subject: Re: Clock drift on Miatas
To: Charles M. Hannum <firstname.lastname@example.org>
From: Hal Murray <email@example.com>
Date: 05/29/2000 14:20:28
> > I think xntpd needs the clock to be within 500 ppm or the PLL won't
> > lock up.
> Is that actually documented anywhere?
I didn't find any clean statement in the html or man page.
It seemed pretty well known in the ntp community. A couple of months
ago I was trying to track down a Linux clock bug on these machines.
One of the first responses I got back pointed out that limit. (That
may be only for the new ntpd vs older xntpd.)
grepping for ppm and 500 in the xntpd sources found this comment
* If the magnitude of the offset is greater than CLOCK_MAX (128
* ms), reset the poll interval and wait for further
* instructions. Note that the cutout switch is set when the
* time is stepped, possibly because the frequency error is off
* planet. In that case all sanity checks are disabled and the
* discipine loop is on its own. Presumably, the loop will
* eventually capture the wayward oscillator (if less than 500
* ppm off planet) and converge, which will then reset the
* cutout switch.
I admit to being somewhat suspicious about my claim given that other
branches have large errors. I assume there would be a few time geeks
running NetBSD who would would have complained if things didn't work