[time-nuts] new member with questions NTP, PRS, GPS, ocxo

Chris Albertson albertson.chris at gmail.com
Sat Aug 18 15:55:14 UTC 2012

> Do you include Sun (now Oracle) Solaris in the list of "others"? I ask
> more out of interest than anything else, but a large proportion of the
> machines here run Solaris. The only two machine that run 24/7, run
> Solaris.
> I've got machines here running CentOS Linux, Solaris (SPARC), Solaris
> (x86), OpenSolaris (x86), AIX (PowerPC), HP-UX (PA-RISC), Windows 7,
> 32-bit Windows XP, 64-bit Windows XP .. plus any I forgot. I used to
> have tru64 and IRIX too, but decided they were a bit old hat.

What is your goal for accuracy?  NTP can be as good as about 2 uSec if
you do everything following best practice.  But you can also use a USB
connected GPS with an indoor antenna and MS Windows for the server and
get in the "handful of milliseconds" range.  That would be three
orders of magnitude worse but still good enough for most uses.

One of the conciderations is how well (and if) the pulse per second
driver is implemented.   Ideally this would be about 12 lines of code
in the interrupt handler.   The last time I used SPARC for an NTP
server it was a 32-bit CPU running SunOS in the pre-solaris days. Si
it was BSD based.  It worked well.

If you want help it would be best to use linux or BSD running on an
Intel CPU.  On that arthitectue the DCD pin on the serial port is tied
to an interrupt controller and it is very simple

Power is a bigger issue.  It really does cost a bit to keep some
machines owered up 24x7 and NTP needs to run all the time.  It takes
NTP hours to stabilize and you want to wait 24 hours after to measure

If you don't need the frquency standard all the time you might use a
lower powered GPS for NTP.  THere are many good ones.  I have a couple
Moterola "UT+" units I got for $18 each.  These output a PPS with 1
sigma error under 100 nanoseconds, better than NTP can use.  The UT+
is tiny, credit card size.   t-bolts use more power because of the
OCXO heater.
Chris Albertson
Redondo Beach, California

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