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In comp.unix.solaris Dave <foo@coo.com> wrote:
> Rick Jones wrote:
> > 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.

Yeah, that probably doesn't help at all...

> 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.

If not, perhaps you could ship the PPS to a second system at each site
and use those as NTP servers.

Or, you find a way to carry IP over this signal being transmitted

> > 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.

In my case, one day I'd like to enable netperf to make direct
measurements of one-way latency.

rick jones
--
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The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway...
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Rick Jones wrote:

<snip>
>
>>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.

FWIW, a few more approaches:

1. If you lack sufficient serial ports, use a terminal server on
ethernet (e.g. Remote Annex, very cheap to acquire on eBay
and elsewhere)

2. If GPS isn't possible at one or more sites, use a WWV/WWVB receiver.

3. A more costly option to operate would be a cellular gateway device, again
cheap on eBay, connected to ethernet.

I use a terminal server with a serial-interfaced remote-controlled HF
receiver to hear WWV for a similar purpose here; the audio drives
sound-card line-in and software decodes the timecode. The many additional
serial ports on the terminal server handle other experimental devices.

Michael

[A complimentary Cc of this posting was sent to
Dave
<foo@coo.com>], who wrote in article <47e0d3cc@212.67.96.135>:
> From those sorts of figures, I suspect I will be stuffed as one will be
> outside with the temperature possibly below 0 deg C and the other in a
> place which might be quite warm.

Hmm... I wonder whether somebody already wrote software to keep the
temperature INSIDE the case at a given level. (Like running fans on
the "indoor" machine like crazy, and do not run them at all on the
"outdoor" one...)

Ilya

> >> I have a requirement where I need two Suns (both Netra T1s) to

> one will be outside with the temperature possibly below 0 deg C and
> the other in a place which might be quite warm.

Have you checked the operating temp range for those systems and
compared that with the expected temps? From a very cursory check if
you get much below 0 deg C you might be pushing the envelope.

rick jones
--
No need to believe in either side, or any side. There is no cause.
There's only yourself. The belief is in your own precision. - Jobert
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

In comp.unix.solaris Dave <foo@coo.com> wrote:
>> The systems will do better if you keep tight control of the temperature.
>
> That is definately not possible. One is going to be outside.

A large box with vent holes can provide an excellent temperature
stabilized environment, especially if someone can monitor it and
open/close vents. It's a bit more fiddly, but very cheap.

--
Darren Dunham ddunham@taos.com
Senior Technical Consultant TAOS http://www.taos.com/
Got some Dr Pepper? San Francisco, CA bay area
< This line left intentionally blank to confuse you. >

Darren Dunham 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. During this time, neither Sun will have internet access and they
>> will not be networked to each other.
>>
>> 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?
>
> Can you simulate the conditions beforehand (with net access)? Run NTP,
> get them all synced up. Enable logs and make sure you have driftfiles
> in place.
>
> On the client "disable ntp" in the config file so that polls are done,
> but the clock is not modified. Let it run that way in simulated
> conditions and see what your drift rate is.
>
> Temperature will likely be the biggest factor in frequency changes.
>
> If temperature is somewhat stable, 500ms should be achievable for a few
> days.

Put the indoor machine in the refrigerator.

RM

Darren Dunham 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. During this time, neither Sun will have internet access and they
>> will not be networked to each other.
>>
>> 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?
>
> Can you simulate the conditions beforehand (with net access)? Run NTP,
> get them all synced up. Enable logs and make sure you have driftfiles
> in place.

One problem is I don't currently have both machines. However, I will be
able to do some testing in this way.

> On the client "disable ntp" in the config file so that polls are done,
> but the clock is not modified. Let it run that way in simulated
> conditions and see what your drift rate is.
>
> Temperature will likely be the biggest factor in frequency changes.

Yes, and I suspect that it could be quite significant.
>
> If temperature is somewhat stable, 500ms should be achievable for a few
> days.
>

I only need it for 4 hours. 500 ms in 4 hours equates to 34.7 ppm, which
is probably expecting a bit much when crystals are not at similar
temperatures.

I thought at first that GPS was not going to be possible, but I'm now
told it might be.

Anyway, lots of people have given me lots of ideas.

Rex Mottram wrote:

> Put the indoor machine in the refrigerator.
>
> RM

Unfortunately, that is not practical given the particular constraints I have

On 2008-03-20, Dave <someplace@nowhere-nice.com> wrote:
> Rex Mottram wrote:
>
>> Put the indoor machine in the refrigerator.
>>
>> RM
>
> Unfortunately, that is not practical given the particular constraints I have

Are the machines close enough together to connect a cable between them?


--
"Be thankful that you have a life, and forsake your vain
and presumptuous desire for a second one."
[email me at huge {at} huge (dot) org <dot> uk]

Huge wrote:
> On 2008-03-20, Dave <someplace@nowhere-nice.com> wrote:
>> Rex Mottram wrote:
>>
>>> Put the indoor machine in the refrigerator.
>>>
>>> RM
>> Unfortunately, that is not practical given the particular constraints I have
>
> Are the machines close enough together to connect a cable between them?
>
>

No - otherwise it would be easy with NTP over ethernet.