[ntp:questions] GPS-PPS, standalone server. NTP
k.fidahasan at gmail.com
Tue Jun 13 11:54:25 UTC 2017
> 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 127.127.20.0 mode 65553 minpoll 5 maxpoll 5
> fudge 127.127.20.0 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.
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 (127.127.28.1) 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.
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