[ntp:questions] PSYCHO PC clock is advancing at 2 HR per second

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Tue Mar 20 18:21:32 UTC 2012

On 3/20/2012 1:25 PM, unruh wrote:
> On 2012-03-20, Ron Frazier (NTP)<timekeepingntplist at c3energy.com>  wrote:
>> On 3/20/2012 2:25 AM, David J Taylor wrote:
>>> "unruh"<unruh at invalid.ca>  wrote in message
>>> news:JDU9r.22132$_C5.11432 at newsfe09.iad...
>>> []
>>>> Of course the question still is why in the world did the system go nuts
>>>> when it was on Local. That itself should not have happened.
>>> If some software had told the system clock to run fast, it simply
>>> stays running fast, even on Local.
>>> Ron is using a single GPS device, over USB, without the backup of a
>>> few Internet servers to stop such a thing happening, and the GPS has
>>> already shown itself to be problematical.  NTP would normally have
>>> simply rejected the errant GPS data and not cause the PC clock to run
>>> wild, but without the Internet servers as backup, what is NTP to do?
>>> I don't think it has a choice other than to believe the GPS, even if
>>> it's incorrect or faulty.
>>> Ron, perhaps in the future you could adopt a similar configuration to
>>> one I've mentioned before - add some Internet servers with a long
>>> polling interval as a second opinion for NTP:
>>> _________________________________________
>>> server<ref clock stuff>
>>> server  0.us.pool.ntp.org  minpoll 10 iburst
>>> server  1.us.pool.ntp.org  minpoll 10 iburst
>>> server  0.uk.pool.ntp.org  minpoll 10 iburst
>>> server  1.uk.pool.ntp.org  minpoll 10 iburst
>>> _________________________________________
>>> using servers [network] local to yourself, of course.
>>> Cheers,
>>> David
>> Hi David T,
>> Eventually, I do plan to have the server preferences as follows:
>> Time server machine:
>>      GPS
>>      Internet as backup
>> Hypothetically speaking, what if I don't want it to distribute time if
>> it's working in internet mode?
>> Non time server machines
>>      GPS (if attached)
>>      Local time server (if available)
> Sorry to shout but NONONONONONONONONONO. Do not use Local time server
> ever, if by local time server you mean LOCL. If you mean a time server
> on your LAN, that is of course fine.

Poor choice of words.  I meant LAN in that case.


>>      Internet as backup
>> However, I only plan to do that after thoroughly testing the GPS by
>> itself for a week or two to see if it's stable.  I originally had the
>> internet servers on with this unit.  It completely surprised me by
>> having this tendency to drift apparently and have periodic heart
>> attacks.  Unfortunately, this odd behavior may exist in all SIRF III and
>> possibly other SIRF units.  It was only by turning off the internet
>> servers that I was able to get some clean graphs of exactly what the GPS
>> was doing.  When I had the internet servers enabled, once the GPS
>> starting acting odd, which it shouldn't do at all, NTPD would clock hop
>> to the internet.  Normally, that would be OK.  However, as discussed
>> previously, even my errant GPS is more accurate over the short term than
>> the internet for me.  With the internet conection, I get + / - 50 ms
>> variations in time over a span of an our.  With the GPS, I get + / - 60
>> ms variations over several days, with a few wild corrections during its
>> heart attacks.  Those are two bad choices, but I think I'd still rather
>> run on the GPS.  The only way I can prevent clock hopping is by
>> noselecting the internet servers.  Even if I end up with internet
>> servers turned on, which I expect to, I think it's much better to know
>> about these GPS anomalies before putting it into long term service.
>> Anybody considering using a SIRF III or maybe even any SIRF unit for
>> timekeeping should be warned by my experience, test the unit, and make
>> sure it's up to the task.  These problems could even affect SIRF units
>> with PPS outputs, although I don't know.  I'll probably decommission
>> this unit from timekeeping duty and relegate it to navigation duty,
>> although I'm not sure how trustworthy it is for that when it's throwing
>> a temper tantrum.
>> I've already committed to getting better (hopefully) equipment.
>> (Shipping from Hong Kong or where ever seems to take a LONG time when
>> you're waiting on something.)  Hopefully, the Sure board will be much
>> more stable and reliable.  I'm planning to do the same extensive testing
> Some apparently ship with bad antennas. Mine craps out often (delivering
> nothing to the unit) maybe some internal loose connection?
> (th blue light stops blinking).
>> on the Sure for a week or two.  I'll start out just plugging the Sure
>> into my serial - USB converter using the same com port as the Globalsat
>> unit was running on.  I want to see how it does with NMEA only data for
>> a while.  I'm hoping NOT to see substantial drifting from UTC and NOT to
>> see any heart attacks every few days.  I expect lots of jitter, since a
>> number of variable length sentences are being output.  Then, I plan to
>> turn off all but GPGGA and test some more, and maybe tinker with the
>> baud rate.  Then, if I can solder the board without killing it, I'll
>> engage PPS through the serial - USB port and test that for a while.
>> Then, I'll try it with PPS and real serial on my other computer, the
>> only one with a serial port.
>> Hopefully, when I'm done, I'll have a qualified unit running stably and
>> accurately for the whole network to use.  I've acquired a case and some
>> hardware to mount the device similar to yours.  Once I learned that it
>> was only 3" x 3", that made me nervous as far as soldering and all, but
>> we'll see what happens.
>> By the way, do you think I should update to Dave H's latest binaries?
>> I'm at 4.2.7p259 on Windows.  Almost all these discussions have been
>> about Windows.  Linux is a whole other ballgame.  The NTPD there from
>> the repositories is about 2 years old, and I'm reluctant to go outside
>> the repositories because of the numerous problems it creates.  One very
>> serious Linux user on a local message board said even he doesn't compile
>> his own programs because of possible problems.  I tried it once and all
>> sorts of scripts and file locations that Ubuntu expects got broken.
>> Sincerely,
>> Ron


(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com

More information about the questions mailing list