David J Taylor wrote:
"Miroslav Lichvar" <mlich...@redhat.com> wrote in message
news:20100311124036.ga22...@localhost...
[]
I did a NTP vs chrony comparison last June with GPS 18x LVC in an
office environment, clock drift was moving in about 0.8ppm range. Here
are distributions of PPS samples received from gpsd:
http://fedorapeople.org/~mlichvar/chrony/chrony_vs_ntp.png
With recent chrony, NTP and kernel versions the results might be
different though.
--
Miroslav Lichvar
Miroslav,
Thanks for that, a most interesting comparison, and thanks to everyone
for their input.
I've recently switched the old (2005) FreeBSD system back on, to see how
well in performs in my own environment. From what's been said, I rather
suspect that were I to go for a more modern, faster, Intel Atom system,
any improvement in accuracy I might get could be swamped by the
temperature changes in the room.
There's also, I will admit, a slight doubt about the effort involved for
the benefit to be gained. With Windows, I am quite happy, and
configuring, using or testing NTP is no problem. With FreeBSD is seems
that the old PPS atom driver has gone, and I may need to configure yet
another driver - gpsd. The number of variants of Linux doesn't help - I
only need a command-line or Telnet interface. And remembering how long
it took to recompile the kernel last time, and the amount of help I
needed to know how to do that, also fills me with doubt.
So I suspect that the performance I'm now seeing from Windows (well
within 100us) may well be "good enough" for me. Perhaps if I get more
free time, and a little more income this year, I may get a
paperback-sized Intel Atom box and see how it does. At least some do
have serial ports! And I would be most interested to hear of anyone who
does configure such a device.
Cheers,
David
100 microseconds is pretty good. Getting the time *into* a computer
takes time and the time taken is not easy to measure.
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