[ntp:questions] Have Pi, have GPS = low powered NTP server?

DaveB g8kbv at uko2.co.uk
Thu Jun 7 10:30:46 UTC 2012

In article <MPG.2a3016d85d1683449896d0 at news.btopenworld.com>, 
spam at goes.nowhere.com says...
> Hi.
> From the title, you might (maybe) guess this is about the Raspberry Pi, 
> and NTP.
> pi at raspberrypi:~$ ntpq -p
> remote           refid         st t when poll reach delay  offset jitter
> ========================================================================
> *ntp.websters-co  2 u  11  128  377 37.918  -7.068  20.879
> +ns1.luns.net.uk  2 u  65  128  377 34.099  -5.716 197.916
> +ns0.luns.net.uk   2 u  64  128  377 33.914  -6.204 181.881
> -time.xilo.net 3 u 101  128  377 25.476 -29.662   4.126
> (A little bit of reformatting to fit here has been done)


I've sort of temporaraly deployed it on the home LAN (literally hanging 
by it's LAN cable!) sync'ing to the existing BSD based time server.

The stat's are now more encouraging, showing delay, offset and jitter 
arround 0.500 units, when left overnight.  See below.

Interestingly, it's decided to cease accessing the few external servers 
I told it about (all uk.pool based) just sticking to the local Stratum 1 
box.  Or they have gone offline now...

pi at raspberrypi:~$ ntpq -p
remote          refid       st t when poll  reach  delay  offset  jitter
*  .GPS.        1 u  362  1024 377    0.563   0.669  0.284
 time.xilo.net  3 -   5h  1024   0   21.571  13.885  0.000
 dns0.rmplc.co  2 -   5h  1024   0 2019.75  -1000.8  0.000

I grabbed that via a remote SSH link, so I know the DSL at home is 
working, else I wouldnt have been able to get this data.  Both the 
external servers were reach=377 when I last looked last night.

If those delay/offset and jitter figures are in milli seconds (?) could 
that be down to the USB hosted LAN port on the Pi?  The same figures for 
the BSD box at are 0.000 0.004 and 0.002 respectively, I 
just remoted into that and checked.

That is using a GPS with PPS via a real COM port, and has a 10/100LAN 
port.  The LAN between the two, is via a 10/100 full duplex switch, a 
generic Netgear domestic plastic 8 port type, nothing special, except 
I've somehow managed to fill all 8 ports!

The next check, will be to use it as a time source itself for one of the 
beacon monitors.  I'll be using the Faros machine for that, as it can 
show me how well the known time references are behaving relative to each 
other, and the received beacon times..

I'm still on a near vertical learning slope with this RasPi thing, and 
Linux in particular, but I do see that other activity (remote access by 
SSH/VNC etc) does not seem to disturb it that much.

Guess I need to look into using the onboard serial port for a GPS at 
some point, if that's releasable from whatever it might be tied to at 
present.  But that would still leave the USB<>LAN behaviour in the loop 
for the downstream users.


Cheers etc.

Dave B.

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