[ntp:questions] NTP with a Serial PPS

Dennis Hilberg, Jr. timekeeper at dennishilberg.com.invalid
Wed Sep 26 16:39:11 UTC 2007


Elio wrote:
> 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  ji
> tter
> =========================================================================
> +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,
> 

Hi,

I run shmpps on Linux with a Garmin GPS 18 LVC, with no problems.

You might try putting the fudge line below the server line as that could be 
what's preventing the SHM peer from showing up in the 'ntpq -p' banner.  I'm 
not an expert, but that's about the only difference between your shmpps 
setup and mine.

######## NTP.CONF FILE ##################

restrict default nomodify

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

#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 ################

Try that.

Regards,

-- 
Dennis Hilberg, Jr.      timekeeper(at)dennishilberg(dot)com
NTP Server Information:  http://saturn.dennishilberg.com/ntp.php




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