Rick Jones wrote:
> In comp.unix.solaris Dave <someplace@nowhere-nice.com> wrote:
>> I have a requirement where I need two Suns (both Netra T1s) to have
>> their clocks close to each other during an experiment that lasts 4
>> hours.
>
> What is your definition of "close?"

I can accept 500 ms, but not any more.

>
>> During this time, neither Sun will have internet access and they
>> will not be networked to each other.
>
> Why then do they need their clocks to remain "close?"

One will be controlling a signal generator's frequency via a GPIB
controller fitted in the Sun. The other Sun will control the frequency
of a receiver via another GPIB controller.

I don't want the situation where the transmitter is at one frequency and
the receiver a couple of GHz away! (The crystals of the transmitter and
receiver will be locked to two rubidium sources, so stability of the
test equipment is not an issue, but somehow I need to ensure the
controllers direct them to the right frequencies at the right time.
Since they are going to be changed every few seconds, I can't put long
delays in the system.

> Will they be in a place where they can receive a GPS signal?

One possibly, the other definitely not Just to make matters worst,
there could be a wide (perhaps 25 deg C) difference in temperature
between the two.

However, you have given me an idea. It should be possible to generate
our own one pulse per second signal from a couple of rubidium
oscillators. However, I'm not sure if the Netra T1's have enough serial
ports, as one will be used to control the Suns. There are two serial
ports are marked "LOM A" and "Serial B". I assume I can can control the
machines from one of these and sync to `1 pps signal on the other, but
I'm not 100% sure of that.

>> I suspect if I sync them by NTP before the experiment starts, then
>> they will not drift by more than 500 ms over a 4 hour period. Does
>> that seem reasonable? Has anyone actually ever made medium term (few
>> hours) stability measurements of the clocks in Suns?
>
> If you get no response in these groups and don't want to simply wait
> four hours and see what happens,

Unfortunately I don't have both machines here.

> you could try asking in
> comp.protocols.time.ntp (if you haven't already).

I will try that. Also the time-nuts mailing list is another possibility.

> rick jones
> wishes his systems were in a place where they could recieve a GPS signal...

Generally I don't have a big issue with time. I sometimes look at the
time of the Sun when I have a train to catch, but generally exact time
is not an issue to me. But this experiment is a bit unusual.