[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO
From: |
Gary E. Miller |
Subject: |
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO |
Date: |
Mon, 21 Oct 2013 10:23:01 -0700 |
Yo Andy!
Wow. Very complete, but I would think beyond where this howto should go.
I would limit this howto to tellthing the user to adjust his fudge until
'ntpq -p' should his local PPS in agreement with good remote chimers.
Getting better than that probably requires renting a traceable standard
time source.
On Mon, 21 Oct 2013 08:34:47 -0400
Andy Walls <address@hidden> wrote:
>
>
> On Mon, 2013-10-21 at 08:00 -0400, Eric S. Raymond wrote:
> > Hal Murray <address@hidden>:
> > >
> > > address@hidden said:
>
> > TODO: more on performance tuning and diagnostics here.
> >
> > This is where we need to talk about (a) adusting fudges, and (b) how
> > to check the quality of your chimers.
>
> WRT adjusting fudges:
>
> http://lists.ntp.org/pipermail/questions/2011-November/030951.html
>
> I happen to use the "calibrate by hand" method mentioned in the post.
> Open-loop is easier for me to follow.
>
> I also have this cheat-sheet lying around for examining the data from
> open-loop tests:
>
> http://www.eecis.udel.edu/~mills/ntp/html/monopt.html
>
> loopstats:
> clock offset (s) offset
> freq offset (PPM) drift compensation
> RMS jitter (s) estimated error
> RMS freq jitter (PPM) stability (aka wander)
> clock poll constant (log2(s)) polling interval
>
> peerstats:
> clock offset (s) offset
> roundtrip delay (s) delay
> dispersion (s) dispersion
> RMS jitter (s) skew (variance)
>
> Show the PPS deviation from system clock. (Keep in mind that
> PPS is probably better than the NTP adjusted system clock.)
>
> gnuplot> plot "peerstats.pps" using ($2):($5) with lines 1
> gnuplot> replot "peerstats.pps" using ($2):($5):($8) with
> gnuplot> yerrorbars 2
>
> Show the GPSD shared memory clock deviations from the system
> clock. (You will get the GPSD shared memory clock fudge value
> estimate from this data when NTP has converged to your
> satisfaction.)
>
> gnuplot> plot "peerstats.shm" using ($2):($5) with lines 1
> gnuplot> replot "peerstats.shm" using ($2):($5):($8) with
> gnuplot> yerrorbars 2
>
> Check the tracking loop convergence (phase):
>
> gnuplot> plot "loopstats" using ($2):($3) with lines 1
> gnuplot> replot "loopstats" using ($2):($3):($5) with
> gnuplot> yerrorbars 2
>
> Check the tracking loop convergence (frequency):
>
> gnuplot> plot "loopstats" using ($2):($4) with lines 1
> gnuplot> replot "loopstats" using ($2):($4):($6) with
> gnuplot> yerrorbars 2
>
> Note that I had run some grep commands to separate PPS peerstats from
> SHM peerstats. Note that I also do not feed PPS to NTP via GPSD, but
> via a /dev/pps device unrelated to the serial port of the GPS (PPS is
> wired to a GPIO).
>
> For estimating GPIO connected PPS fudge, an experiment in measuring
> GPIO IRQ latency is needed (something like this:
> https://github.com/scottellis/overo-irqlat )
>
>
> Regards,
> Andy
>
>
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
address@hidden Tel:+1(541)382-8588
signature.asc
Description: PGP signature
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, (continued)
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Gary E. Miller, 2013/10/21
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Hal Murray, 2013/10/21
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Eric S. Raymond, 2013/10/21
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Andy Walls, 2013/10/21
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO,
Gary E. Miller <=
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Eric S. Raymond, 2013/10/23
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Andy Walls, 2013/10/23
- Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Eric S. Raymond, 2013/10/24
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Gary E. Miller, 2013/10/21
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Eric S. Raymond, 2013/10/22
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Gary E. Miller, 2013/10/22
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Beat Bolli, 2013/10/22
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Eric S. Raymond, 2013/10/22
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Gary E. Miller, 2013/10/22
Re: [gpsd-dev] Clarifications needed for the time-service HOWTO, Eric S. Raymond, 2013/10/22