[ntp:questions] ntpd NMEA / PPS on linux kernel 3.18+ - PPS broken ?

Brandon Applegate brandon at burn.net
Thu Jan 21 04:11:21 UTC 2016


Hello,

I upgraded a box from Ubuntu 12.04 to 14.04 today - and with that came a new kernel (as one would expect).  Unfortunately - it looks like something has changed / broken in or around kernel 3.18 WRT PPS in the kernel.

Jan 20 22:36:52 ice ntpd[4383]: refclock_params: time_pps_kcbind: Operation not supported
Jan 20 22:36:52 ice ntpd[4383]: GPS_NMEA(0) set PPSAPI params fails

Here’s a few other folks seemingly hitting this issue as well:

http://lists.ntp.org/pipermail/hackers/2015-February/006709.html <http://lists.ntp.org/pipermail/hackers/2015-February/006709.html>

https://www.raspberrypi.org/forums/viewtopic.php?t=94385&p=658670 <https://www.raspberrypi.org/forums/viewtopic.php?t=94385&p=658670>

The first one seems to be this issue dead on.  The bad news is it still seems present.  I’ve tried both the latest stable and -dev - same results.  My PPS and NMEA is working.

root at ice:/home/vom# head -1 /dev/gps0
$GPRMC,040034,A,XXXX.8154,N,0XXXX.8217,W,000.0,000.0,210116,005.6,W*70

root at ice:/home/vom# ppstest /dev/gpspps0
trying PPS source "/dev/gpspps0"
found PPS source "/dev/gpspps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1453348999.005571278, sequence: 4974 - clear  1453348999.205597303, sequence: 1511
source 0 - assert 1453349000.005695448, sequence: 4975 - clear  1453348999.205597303, sequence: 1511
source 0 - assert 1453349000.005695448, sequence: 4975 - clear  1453349000.205719599, sequence: 1512

Here’s my relevant refclock lines from ntp.conf that was working a few hours ago when I was on 12.04:

# gps / pps
server 127.127.20.0 mode 1 minpoll 4 maxpoll 4
fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 time2 0.600

What I don’t see in any of the thread above is a solution :(  The kernel on my 14.04.3 install is:

Linux ice 3.19.0-47-generic #53~14.04.1-Ubuntu SMP Mon Jan 18 16:09:14 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

I’ve seen the fudge flag3 referred to as ‘hard PPS’.  My frustration comes from the fact that this was working fine on an older kernel (I’m assuming this is a kernel bug).

So if this has been fixed > 3.18 or 3.19 - Ubuntu will push a newer kernel in the train for the next 14.04.x bump (scheduled for next month I believe)...

Has anyone been bitten by this and overcame it ?

PS: If this is truly a kernel bug - I appreciate that the ntp folk aren’t on the hook for any fixes - but certainly if anyone would know the scoop it’s this list.

--
Brandon Applegate - CCIE 10273
PGP Key fingerprint:
830B 4802 1DD4 F4F9 63FE  B966 C0A7 189E 9EC0 3A74
"SH1-0151.  This is the serial number, of our orbital gun."

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