[ntp:questions] ntp on ubuntu 12.10 with gps and pps.

Paul J R me at pjr.cc
Mon Apr 8 09:55:55 UTC 2013


Im running an intel atom also (old one, d945gclf2 board), and its only 
doing ntp at the moment with a fairly minimal 64bit ubuntu 12.10 server.

after 24 hours its now looking like this:

      remote           refid      st t when poll reach   delay offset  
jitter
============================================================================== 

+203.0.178.191   43.128.117.84    2 u   38   64  377    8.960 -11.714   
0.169
*27.54.95.12     218.100.43.70    2 u   31   64  377   61.301 -1.256   
0.246
-202.6.248.7     130.102.128.23   3 u   46   64  377    9.529 -0.273   
0.160
-116.66.162.4    130.234.255.83   2 u   52   64  377   20.386 15.747   
1.988
+121.0.0.41      204.152.184.72   2 u   59   64  377   25.295 -4.202   
3.760
o127.127.20.0    .GPS.            0 l    1    8  377    0.000 -0.001   
0.001

I've just tuned the gps so that its only outputing a single nmea 
sentence (GPZDA) and increased the speed to 9600 and now its no longer 
needing the fudge factor. Ultimately though, i'll want to try get it 
running from a geode based machine (which has some seriously low specs, 
but it'll be amusing to see how it performs).

Something else i've noticed as well when im watching it, when it adjusts 
the system time it seems to impact the jitter calculation quite 
considerably and with the other ntp servers in there, it doesnt always 
seem to want to choose the gps as the absolute truth.

On 07/04/13 23:46, David Taylor wrote:
> On 07/04/2013 11:14, Paul J R wrote:
>> Hi All,
>>
>> I've got a SiRF star 3 GPS with a PPS line which im trying to get
>> running on a machine with ubuntu 12.10 and a serial port using the DCD
>> line for pps signalling.
> []
>> o127.127.20.0    .GPS.            0 l 4    8  377    0.000 -0.065
>> 0.003
> []
>> Seems like a pretty decent little gps unit, assuming i've got it
>> functioning and configured correctly?
>
> Just for comparison:
>
> Intel Atom PC running FreeBSD 8.2 (Pixie):
> o127.127.20.1    .PPS. offset/jitter -0.001   0.002
>
> Two Raspberry Pis running Linux 3.2.27+
> o127.127.22.0    .PPS. offset/jitter 0.002   0.002
> o127.127.22.0    .PPS. offset/jitter 0.001   0.002
>
> Raspberry Pi running Linux 3.36.11
> o127.127.22.0    .PPS. offset/jitter 0.000   0.002
>
> 65 microseconds offset seems a little high to me, but the PCs I've 
> just quoted are all (mostly) /only/ serving NTP.  I have been doing a 
> little installation work on Raspberry Pi #3 today, and it now has a 
> steady CPU and network I/O load.  Its PPS was only configured 
> yesterday. Performance graphs are here:
>
>   http://www.satsignal.eu/mrtg/performance_ntp.php
>
> I hope that helps your comparisons.




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