gpsd with ntpd and PPS works only if in ntp.conf is a additional external server

[Kai Klenke]

 

Hello,

i am using the ublox "Antaris LEA-4H"-GPS-Receiver and it is via RS232
connected to the gpsd on a Linux-Debian-Lenny machine.

The GPS-Receiver is configured to 38400 baud 8-N-1 with standard NMEA output
(only GPGGA and
GPRMC are activated).

Additional the DCD is pulsed by the receiver with 900ms logical 0 and 100ms
logical 1.

The ntpd is ocnfigured via ntp.conf as followed:

server 127.127.28.0 minpoll 4 maxpoll 4
fudge 127.127.28.0 time1 0.450 refid GPS

server 127.127.28.1 minpoll 4 maxpoll 4 prefer
fudge 127.127.28.1 refid PPS

! There are no more other server-Lines !

The gpsd sees the NMEA strings and the PPS signal.

gpsd: GPRMC starts a reporting cycle.
gpsd: GPRMC sets mode 2
gpsd: ntpshm_put: Clock: 1253006881 @ 1253006881.439076
gpsd: <= GPS:
$GPGGA,092801.00,5306.13903,N,00851.51417,E,1,11,4.09,8.6,M,46.4,M,,*59
gpsd: GPGGA sets status 1 and mode 3 (changed)
gpsd: pps-detect (DCD) on /dev/ttyS0 changed to 1
gpsd: ntpshm_pps: lost PPS lock
gpsd: PPS pulse. cycle: 999998, duration: 899999
gpsd: pps-detect (DCD) on /dev/ttyS0 changed to 0
gpsd: ntpshm_pps: lost PPS lock
gpsd: PPS pulse. cycle: 999976, duration: 99977
gpsd: <= GPS:
$GPRMC,092802.00,A,5306.13903,N,00851.51418,E,0.007,,150909,,,A*7F

Now if ntpd and gpsd are running the ntpq -p shows following things:

remote   refid      st t when poll reach  delay    offset  jitter
=========================================================================
*SHM(0)  .GPS.      0 l   13   16  377    0.000    0.885   0.882
 SHM(1)  .PPS.      0 l   -    16  0      0.000    0.000   0.001

The GPS-Line is works fine, but the PPS shows no changes.

I thought if the line "ntpshm_put: Clock: 1253006881 @ 1253006881.439076"
the gpsd writes data to the shared memory.

If i now add the line..

server 1.debian.pool.ntp.org iburst dynamic

to the ntp.conf, then restart ntpd with..

"/etc/init.d/ntp stop" and "/etc/init.d/ntp start" (the gpsd is still
running during these
changes)

i can see that the gpsd output changes:

gpsd: GPRMC starts a reporting cycle.
gpsd: GPRMC sets mode 2
gpsd: ntpshm_put: Clock: 1253084169 @ 1253084169.129956
gpsd: <= GPS:
$GPGGA,065609.00,5306.13990,N,00851.51074,E,1,09,2.06,10.1,M,46.4,M,,*62
gpsd: GPGGA sets status 1 and mode 3 (changed)
gpsd: pps-detect (DCD) on /dev/ttyS0 changed to 0
gpsd: ntpshm_pps: clock: 1253084170 @ 1253084169.930675, precision -3
gpsd: PPS pulse. cycle: 999480, duration: 899538
gpsd: pps-detect (DCD) on /dev/ttyS0 changed to 1
gpsd: ntpshm_pps: clock: 1253084170 @ 1253084170.030620, precision -5
gpsd: PPS pulse. cycle: 999483, duration: 99945
gpsd: <= GPS:
$GPRMC,065610.00,A,5306.13991,N,00851.51076,E,0.044,137.85,160909,,,A*6F

Now the line "ntpshm_pps: lost PPS lock" does not appear and after
approximately 30
seconds the PPS is used by ntpd.

I wondered, how can improve an additional server in the ntp.conf the
evaluation of the PPS signal by the gpsd?

It must be an external server in the ntp.conf the "Undisciplined Local
Clock"
as NTP reference clock does not work.

Kai



 





Kai

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