[ntp:questions] GPS-PPS, standalone server. NTP

Fida Hasan k.fidahasan at gmail.com
Tue Jun 13 11:54:25 UTC 2017

> Hi, 
> My 18x is linked with an Odroid C1+ and I use only driver 20 with 0x10000 mode enabled to have a better look on NMEA sentences. It's by looking 'ntpq -c clockvar' results that I discovered the quality of my 18x comparing with some others 'Adafruit' or basic GPS chips.
> from my ntp.conf:
> server mode 65553 minpoll 5 maxpoll 5 
> fudge time2 0.550 flag1 1 flag3 1 flag4 1  
> Knowing that by default flags are set to 0 I don't explicitly feel the need to reset them again to 0. 
> Having only one physical device (GPS) connected I also don't feel the need to rename the driver with 'refid' option. 
> Jean-Michel

Hi Jean-Michel,
You came up with so many good information. Thank you so much. Regarding this specific point you did not say how accuracy you got through the driver 20 (both with/without internet)?
In my understanding, Driver 20 gives NMEA sentences and its accuracy suppose to fluctuates in millisecond range! 

I am very keen to get a stable clock with 1 micro accuracy. Aiming this I have tested many settings.
According to my achievement, I have got:
1. 1 micro accuracy in driver 22! 
2. then I compiled the kernel and get nano second level accuracy in driver 22! Though it fluctuates in microsecond range as well, not stable but average I was able to develop around 800ns there.

But in driver 22, it is just merely a precise tick without time, my system always follows driver 20 (showed asterisk on it *). But still I can't develop microsecond accuracy on it. 

My question, if I can't develop microsecond accuracy on the usable reference ID, then what's the point of saying GPS is as accurate as microsecond?

However, I have got a link here,
According to this site, it uses shared driver 28 ( to develop achievable accuracy in microsecond range (follow the asterisk).

  remote           refid      st t when poll reach   delay   offset  jitter
+SHM(0)          .GPS.            0 l    6   16  377    0.000   28.775  10.971
*SHM(1)          .PPS.            0 l    5   16  377    0.000   -0.001   0.002

However, I haven't able to develop it yet, for some reasons it is not working with my Rpi system! 

Will appreciate your further comment at this stage.
Kind Regards,

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