Re: [gpsd-dev] [PATCH] Improve chrony examples in time howto.

[Miroslav Lichvar]

On Mon, Nov 04, 2013 at 11:30:44AM -0500, Greg Troxel wrote:
> Miroslav Lichvar <address@hidden> writes:
> > Any suggestions on how to rephrase it? The problem is the uncorrected
> > frequency. The time error of the clock has a sawtooth profile with
> > amplitude proportional to the drift of the clock. If the drift is in
> > single digit ppm, perhaps the error may be acceptable, but I'm not
> > really sure.
> 
> I would try to explain it clearly and be quantitative.  There is a trend
> in timekeeping to be horrified at the last ns, even though hardly anyone
> comes close; I think people should be aware of errors and manage them as
> an engineering exercise).

Ok. I'll see if I can come up with something.

> IF you mean chrony uses RFC1589 ntp_adjtime on Linux, and not on other
> systems, that sounds buggy, as other systems have ntp_adjtime.

Well, I'd say it's a lack of support. On Linux it uses the extended
version of ntp_adjtime() called adjtimex(). Also, it needs to know
some details about the implementation in the kernel, e.g. when and how
are the corrections applied. I guess the NetBSD implementation is
closer to the reference nanokernel by David Mills than Linux and
wouldn't be very difficult to support, but it's not something that can
be enabled just by compiling the Linux driver code.

-- 
Miroslav Lichvar