[LinuxPPS] ntptime status - relaunch of that issue

[Hal V. Engel]

On Monday 16 February 2009 11:26:44 pm Felix Joussein wrote:
> Hello list,
>
> as I am really blocked out right now in my work, I re-launch my
> question/issue regarding the ntptime status codes...
>
> Additionally to these facts mentioned below, I have made the following
> observations during my comparison of the "should be" state and the "is"
> state, apart from the status codes which prove, to me, that my setup is
> messy:
>
> So additionally to the ntptime output already mentioned, the interval
> stands still, always on 1s. On my ppsKit machines running on linux 2.4
> the interval is increasing up to 256, also the offset and jitter from
> ntpq-p -c rl for the pps source should not bounce more then from 0,001
> to 0,010.
> In my case it bounces from around -0,150 to 0,150.

I don't see this on my machine.  After startup it takes about 1/2 hour to 
stabilize and once it is stable my jitter is typically around 1 or 2 
microseconds and my offsets are almost aways <20 microseconds.  So there is 
definitely an issue on your configuration or hardware if your jitter is as 
high as 150 microseconds.  

What the cause is I don't know.  But looking at your configure command for ntp 
I do see some differences from what I used and what is recommended in the 
wiki.  Specifically I have not used ac_cv_var_tick=no, ac_cv_var_tickadj=no, 
--enable-accurate-adjtime or --enable-linuxcaps.  I don't know what these do 
or how they affect how ntp interacts with LinuxPPS.  I think most LinuxPPS 
users are not using any of these configure settings.

I think that the PPSKit patches implemented an in kernel time keeping consumer 
(IE. time_pps_kcbind()).  LinuxPPS does not since this functionality is 
optional.  This is the likely explanation for the interval always being 1s and 
the missing PPS related status codes.   There have been some discussions here 
about this but no one has stepped forward to implement this functionality and 
this is very likely not a trivial undertaking. 

>
> I am for 100% sure, it is not my pps source, as I used on the one hand a
>  real atom clock and in the lab a garmin 18lvc.
> Both sources work as expected under my old Linux 2.4 setup.
>
> Also the rest of the hardware is not the problem... neither on a Pentium
> M 1.7GHz nor on an amd64, same on both machines...
>
> Here is my previous post.
> Please help me to get this work!
>
>
> many regards,
>
> Felix
>
>
> I have running ntp-4.2.4p4, built with the following options:
> ./configure CFLAGS='$(CFLAGS)' \
>                 ac_cv_var_tick=no ac_cv_var_tickadj=no \
>                 --prefix=/usr \
>                 --enable-all-clocks --enable-parse-clocks --enable-SHM \
>                 --enable-ATOM --enable-accurate-adjtime --with-crypto \
>                 --sysconfdir=/etc \
>                 --enable-debugging \
>                 --with-sntp=no \
>                 --enable-linuxcaps \
>                 --disable-dependency-tracking
>
>
> My Kernel ist 2.6.28 with the corresponding pps patch.
>
> The output of ntptime is:
>
> ntp_gettime() returns code 0 (OK)
>   time cd3455ac.081b5418  Wed, Feb  4 2009 18:58:04.031, (.031667534),
>   maximum error 13322 us, estimated error 52 us, TAI offset 34
> ntp_adjtime() returns code 0 (OK)
>   modes 0x0 (),
>   offset -11487.545 us, frequency -25.923 ppm, interval 1 s,
>   maximum error 13322 us, estimated error 52 us,
>   status 0x2001 (PLL,NANO),
>   time constant 4, precision 0.001 us, tolerance 500 ppm,
>
> I'm concerned about the status 0x2001 (PLL,NANO) because when I use a
> 2.4.33.2 kernel with the ppskit, same ntp version, same configure
> options, ntptime gives the following output:
>
> ntp_gettime() returns code 0 (OK)
>   time cd34564c.6f9324e4  Wed, Feb  4 2009 18:00:44.435, (.435839520),
>   maximum error 529 us, estimated error 1 us, TAI offset 134514656
> ntp_adjtime() returns code 0 (OK)
>   modes 0x0 (),
>   offset 2.688 us, frequency -108.801 ppm, interval 256 s,
>   maximum error 529 us, estimated error 1 us,
>   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
>   time constant 4, precision 0.448 us, tolerance 496 ppm,
>   pps frequency -108.801 ppm, stability 0.012 ppm, jitter 2.063 us,
>   intervals 14986, jitter exceeded 6916, stability exceeded 258, errors 16.
>
> The  status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO) is different.
>
> What makes the difference, at which part of the howto from
> http://wiki.enneenne.com/index.php/LinuxPPS_installation
> might I have not followed correctly?
>
> Thank you for your help,
>
> Felix
>
>
>
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