Re: [gpsd-users] Enable PPS Echo

[hans mayer]

dear Reto,

> Therefore we might assume, that the PPS processing is quite accurate

definitely

> It's an asymmetrical cable link with 200 / 20 MBit/s and the average
>  round-trip-time to the NTP is about 9 ms.

speed difference has a factor of 10. this is quite similar to
my ADSL situation. but your RTT is much smaller.
therefore i assume you offset will be only between 2 or 3 ms
or maybe near 2 ms.

> Maybe it's easier to take the box to my workplace and compare
> it to the Meinberg NTP which we're running on the LAN.

this is absolute the best way.
but even comparing to a stratum 1 server in the internet will show you
a different and better result if the internet connectivity is symmetric.


// hans

--


Am 06.04.2016 01:32, schrieb Reto Zbinden ST:
> Hello Hans
>
> Thanks for this very interesting article. Therefore we might assume, that the 
> PPS processing is quite accurate (even on a slow ALIX box) and delay is mainly 
> introduced by the internet connection. It's an asymmetrical cable link with 200 
> / 20 MBit/s and the average round-trip-time to the NTP is about 9 ms.
>
> Mainly because of my personal interest, I thought it would be interesting to do 
> some (simple) measurements and to learn more about the processing time of the 
> hardware I'm using. Maybe it's easier to take the box to my workplace and 
> compare it to the Meinberg NTP which we're running on the LAN.
>
> Regards
> Reto
>
> -----Ursprüngliche Nachricht-----
> Von: address@hidden [mailto:address@hidden Im Auftrag von hans mayer
> Gesendet: Dienstag, 5. April 2016 22:51
> An: address@hidden
> Betreff: Re: [gpsd-users] Enable PPS Echo
>
>
>
> Dear Reto,
>
> How is your Internet connectivity ?
> Is it maybe ADSL ?
> If so look here:  http://blog.mayer.tv/2016/03/16/ntp-and-adsl.html
>
> Kind regards
> Hans
>
>
>
> Am 05.04.2016 18:17, schrieb Reto Zbinden ST:
> > Dear all
> >
> > I'm not really sure if this is the right place for my question, but maybe 
> > somebody may help me:
> >
> > I'm running Debian with gpsd and ntpd on an older ALIX board as the time source 
> > for my local network. This setup is working well for quite some time and the 
> > clock is kept to within a few microseconds of the 1PPS reference.
> >
> > But if the time is compared to some reliable public stratum 1 servers (e.g. 
> > metas.ch), it seems that the local clock is always a few milliseconds behind 
> > these servers. I'd like to do some more precise measurement to figure out the 
> > latency of the 1PPS signal processing and to adjust the fudge time. According 
> > to what I've read, the delay can be measured using an oscilloscope and the PPS 
> > echo feature. But I couldn't figure out how the echo function can be activated.
> >
> > Can anyone provide some guidance on how to enable the PPS echo function? Or 
> > maybe there's another way to do some measurements? Many thanks for your help.
> >
> > Regards
> > Reto