[ntp:questions] NTP with a Serial PPS

Elio elio.gi at gmail.com
Tue Sep 25 12:03:31 UTC 2007


Hi to all,
my name is Elio and I work in an Italian seat of the Nokia Siemens Network.

We're making some tests on NTP and we want to use a GPS as a Primary
Ref. Clock in order to synchronize an NTP Stratum 1 PC.

The starting point was Philip M. White documentation called "Using a
Garmin GPS 18 LVC as NTP stratum-0 on Linux 2.6".
The linux kernel that I use is a 2.6.18 version. I've downloaded the
last version of ntp (4.2.4p4) and configured it with the options
"--disable-all-clocks --disable-parse-clocks --enable-SHM
--enable-linuxcaps"; after I've compiled and installed it.

We've prepared also a cable that connect a PPS (TTL) signal from a BNC
connector with a RS-232 (with pins 1 DCD and 5 GND; we've also tried
with pins 9 and 5, modifying the driver shmpps).

The shmpps output seems to work, so "shmat ok" message appears and
also messages like these appears:
range:4-11 sys:1144597205/3044 ref:1144597205/0 prec: -11
range:5-12 sys:1144597219/3310 ref:1144597219/0 prec: -11
range:5-12 sys:1144597233/3546 ref:1144597233/0 prec: -12
range:3-10 sys:1144597247/3739 ref:1144597247/0 prec: -12
range:3-10 sys:1144597261/3954 ref:1144597261/0 prec: -13
range:5-12 sys:1144597275/4158 ref:1144597275/0 prec: -13
range:4-11 sys:1144597289/4042 ref:1144597289/0 prec: -14
range:2-9 sys:1144597303/3801 ref:1144597303/0 prec: -14
range:4-11 sys:1144597317/3619 ref:1144597317/0 prec: -14

but when I type the command "ntpd –p" the output is the following:

      remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+mchm932a.siemen 139.25.228.79    3 u   15   16  377   31.581  -11.909   1.941
+blns064x.bln.sb .GPS.            1 u    -   16  377   45.182    0.229   0.271
*mhpa6hjc.mch.sb .PPS.            1 u    4   16  377   32.284    0.522   0.254

So not appears a line similar to :

*SHM(0)          .PPS.            0 l   13   16  377    0.000   -0.015   0.004

Are possible some configuration errors?
Have I omitted some steps in the settings or in the configuration?
Do you think that there could be an error only in the ntp configuration?

It follows my ntp.conf file content:
######## NTP.CONF FILE ##################

restrict default nomodify

restrict 127.0.0.1
fudge 127.127.28.0 refid PPS flag3 1
server 127.127.28.0 minpoll 4 prefer

#OUR INTERNAL NETWORK TIMESERVERS

server 139.25.228.82 minpoll 4 maxpoll 4
#Stratum 1 GPS
server 147.54.45.7 minpoll 4 maxpoll 4
#Server Stratum1 CESIUM
server 139.25.66.22 minpoll 4 maxpoll 4

driftfile /var/lib/ntp/drift
broadcastdelay  0.008

keys            /etc/ntp/keys    # this file is empty
############## ENDOFFILE ################

Sure of a rapid reply…
Thanks in advance.
Best Regards,

-- 
Elio



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