[ntp:questions] How to get shared memory access from gpsd to ntpd to work?

Charles Elliott elliott.ch at comcast.net
Tue Aug 22 12:50:37 UTC 2017


For one thing, 10110 may be the wrong port number to use: "The registered ports are those from 1024 through 49151. IANA maintains the official list of well-known and registered ranges.[3] The dynamic or private ports are those from 49152 through 65535. One common use for this range is for ephemeral ports." (https://en.wikipedia.org/wiki/Port_(computer_networking))  Second, port 10110 may be reserved for NMEA-0183 Navigational Data (on GPS devices).  See https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml? <https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?&page=117> &page=117.  You might want to consider a port number in [49152, 65535] on 192.168.13.100, if that is your computer’s IP address.  I am referring to these error messages:

 

> Aug  6 19:28:16 computer gpsd[374]: gpsd:ERROR: UDP device open error can't connect to host/port pair.

> Aug  6 19:28:16 computer gpsd[374]: gpsd:ERROR: initial GPS device 

> udp://192.168.13.100:10110 open failed Aug  6 19:28:16 computer 

 

Third, you may want to try to limit the GPS output to just $GPRMC messages.  That is the only NMEA message NTPD needs; it has to sort through all the other messages to find $GPRMC, and it sometimes becomes confused doing so, since characters are put in a buffer one at a time, and the computer reads the buffer almost instantaneously, only part of a message may be returned to NTPD, i.e., one complete message plus a fragment of another.  If I recall correctly, part of the 127.127.28.1 clock indicator tells NTPD which NMEA message to look for, but in any case there is a code for it.  I believe there is a standard NMEA message to limit the rates of the various messages a GPS device will output.  Just limit the rates of all but $GPRMC to zero.  You can find a an NMEA manual by searching for it on the Internet.

 

I agree with the person who wrote that he had never heard of accessing a GPS device with UDP; NTPD is not set up for that, although using shared memory may be a good workaround.  I am not so sure of the PPS signal coming in that way though.  NTPD is set to detect PPS from the rising or falling edge of a single RS-232 port pin, DCD if I recall correctly.

 

Charles Elliott

                                                                                          

-----Original Message-----
From: questions [mailto:questions-bounces+elliott.ch=comcast.net at lists.ntp.org] On Behalf Of juergen perlinger
Sent: Monday, August 21, 2017 4:06 AM
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] How to get shared memory access from gpsd to ntpd to work?

 

On 08/16/2017 02:52 PM, Etaoin Shrdlu wrote:

> Hi all,

> 

> I've been battling for some time with getting ntpd to set the 

> date/time from gpsd's shared memory locations. My GPS device is on the 

> network and sends GPS messages every minute over UDP. This is picked 

> up by gpsd and it appears I get a good fix with all the required data. 

> It also looks as if the shared memory locations are being set up 

> correctly. But whatever I do, ntpd time source "reach" stubbornly 

> remains at zero, even when running ntpd as root. I would be most 

> grateful if someone could cast their eyes on the configurations and 

> log output below, and let me know if you can see were it's going wrong!

 

I didn't look to close, but there's an alternative using driver 46 and the JSON API of GPSD. It's a bit easier to set up.

 

> 

> P.S. This has been cross-posted from  <mailto:gpsd-users at nongnu.org> gpsd-users at nongnu.org, where I 

> failed to get any response to my query.

> 

> 

> # syslog gpsd startup: 

> 

> Aug  6 19:28:16 computer gpsd[374]: gpsd:INFO: launching (Version 

> 3.11) Aug  6 19:28:16 computer gpsd[374]: gpsd:INFO: listening on port 

> gpsd Aug  6 19:28:16 computer gpsd[374]: gpsd:PROG: NTPD shmat(0,0,0) 

> succeeded, segment 0 Aug  6 19:28:16 computer gpsd[374]: gpsd:PROG: 

> NTPD shmat(32769,0,0) succeeded, segment 1 Aug  6 19:28:16 computer 

> gpsd[374]: gpsd:PROG: NTPD shmat(65538,0,0) succeeded, segment 2 Aug  

> 6 19:28:16 computer gpsd[374]: gpsd:PROG: NTPD shmat(98307,0,0) 

> succeeded, segment 3 Aug  6 19:28:16 computer gpsd[374]: gpsd:PROG: 

> successfully connected to the DBUS system bus Aug  6 19:28:16 computer 

> gpsd[374]: gpsd:PROG: shmat() succeeded, segment 131076 Aug  6 

> 19:28:16 computer gpsd[374]: gpsd:PROG: shared-segment creation succeeded, Aug  6 19:28:16 computer gpsd[374]: gpsd:INFO: stashing device udp://192.168.13.100:10110 at slot 0 Aug  6 19:28:16 computer gpsd[374]: gpsd:INFO: opening UDP feed at 192.168.13.100, port 10110.

> Aug  6 19:28:16 computer gpsd[374]: gpsd:ERROR: UDP device open error can't connect to host/port pair.

> Aug  6 19:28:16 computer gpsd[374]: gpsd:ERROR: initial GPS device 

> udp://192.168.13.100:10110 open failed Aug  6 19:28:16 computer 

> gpsd[374]: gpsd:INFO: running with effective group ID 20 Aug  6 

> 19:28:16 computer gpsd[374]: gpsd:INFO: running with effective user ID 

> 110 Aug  6 19:28:16 computer gpsd[374]: gpsd:INFO: startup at 

> 2017-08-06T19:28:16.000Z (1502047696)

> 

> # syslog ntpd startup:

> 

> Aug  6 19:28:24 computer ntpd[609]: ntpd  <mailto:4.2.6p5 at 1.2349-o> 4.2.6p5 at 1.2349-o Mon Jul 25 

> 22:35:28 UTC 2016 (1) Aug  6 19:28:24 computer ntp[582]: Starting NTP server: ntpd.

> Aug  6 19:28:24 computer ntpd[652]: proto: precision = 0.781 usec Aug  

> 6 19:28:24 computer ntpd[652]: Listen and drop on 0 v4wildcard 0.0.0.0 

> UDP 123 Aug  6 19:28:24 computer systemd[1]: Started LSB: Start NTP daemon.

> Aug  6 19:28:25 computer ntpd[652]: Listen and drop on 1 v6wildcard :: 

> UDP 123 Aug  6 19:28:25 computer ntpd[652]: Listen normally on 2 lo 

> 127.0.0.1 UDP 123 Aug  6 19:28:25 computer ntpd[652]: Listen normally 

> on 3 eth0 192.168.13.100 UDP 123 Aug  6 19:28:25 computer ntpd[652]: 

> Listen normally on 4 lo ::1 UDP 123 Aug  6 19:28:25 computer 

> ntpd[652]: Listen normally on 5 eth0 fe80::6a89:f1d3:7ec0:510 UDP 123 

> Aug  6 19:28:25 computer ntpd[652]: peers refreshed Aug  6 19:28:25 

> computer ntpd[652]: Listening on routing socket on fd #22 for 

> interface updates

> 

> # syslog gpsd sample: 

> 

> Aug  6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPGGA,185748.0,1234.567890,N,00012.345678,E,1,10,0.9,13.6,M,47.0,M,,*

> 6B Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: GPGGA sentence 

> timestamped 185748.00.

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: GPGGA starts a reporting cycle.

> Aug  6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPRMC,185748.0,A,1234.567890,N,00012.345678,E,0.0,,060817,0.0,E,A*2B

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: GPRMC sentence timestamped 185748.00.

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: GPRMC ends a reporting cycle.

> Aug  6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPVTG,,T,0.0,M,0.0,N,0.0,K,A*0D Aug  6 19:56:42 computer gpsd[374]: 

> gpsd:IO: <= GPS: 

> $GPGSA,A,2,01,03,06,09,11,17,19,22,23,31,,,1.2,0.9,0.8*31

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: GPGSA sets mode 2 Aug  

> 6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPGSV,4,1,13,01,31,136,41,03,67,068,35,06,32,303,31,09,34,202,41*78

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: Partial satellite data (1 of 4).

> Aug  6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPGSV,4,2,13,11,09,153,39,17,40,243,40,19,42,272,30,22,42,082,40*78

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: Partial satellite data (2 of 4).

> Aug  6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPGSV,4,3,13,23,61,174,46,31,19,047,36,12,04,329,,14,00,039,*76

> Aug  6 19:56:42 computer gpsd[374]: gpsd:PROG: Partial satellite data (3 of 4).

> Aug  6 19:56:42 computer gpsd[374]: gpsd:IO: <= GPS: 

> $GPGSV,4,4,13,25,01,001,*4C

> 

> 

> # /etc/default/gpsd

> 

> START_DAEMON="true"

> USBAUTO="false"

> DEVICES="udp://192.168.13.100:10110"

> GPSD_OPTIONS="-n -D5"

> 

> 

> # ntpd.conf: 

> 

> GPS Serial data reference (NTP0)

> server 127.127.28.0 minpoll 4 maxpoll 4 prefer fudge 127.127.28.0 

> time1 0.0 refid GPS

> 

> GPS PPS reference (NTP1)

> server 127.127.28.1 minpoll 4 maxpoll 4 prefer fudge 127.127.28.1 

> refid PPS

> 

> 

> # ntpq -p                                                                                                                                         Sun Aug  6 19:48:25 2017

> 

>      remote           refid      st t when poll reach   delay   offset  jitter

> ==============================================================================

>  SHM(0)          .GPS.            0 l    -   16    0    0.000    0.000   0.000

>  SHM(1)          .PPS.            0 l    -   16    0    0.000    0.000   0.000

> 

> 

> # cat /proc/sysvipc/shm                                                                                                                           Sun Aug  6 19:30:45 2017

> 

>        key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime        rss       swap

> 1314148400          0   600         80   374   652      2     0     0     0     0 1502047705          0 1502047696       4096          0

> 1314148401      32769   600         80   374   652      2     0     0     0     0 1502047705          0 1502047696       4096          0

> 1314148402      65538   666         80   374   374      1     0     0     0     0 1502047696          0 1502047696          0          0

> 1314148403      98307   666         80   374   374      1     0     0     0     0 1502047696          0 1502047696          0          0

> 1196446532     131076   666      31616   374   374      1     0     0     0     0 1502047696          0 1502047696          0          0

> 

> 

> # gpsmon:

> 

> tcp://localhost:2947          JSON slave driver>

> (83) 

> {"class":"VERSION","release":"3.11","rev":"3.11-3","proto_major":3,"pr

> oto_minor":9}

> (125) 

> {"class":"DEVICES","devices":[{"class":"DEVICE","path":"udp://192.168.

> 13.100:10110","activated":"2017-08-06T19:31:50.526Z"}]}

> (122) 

> {"class":"WATCH","enable":true,"json":false,"nmea":false,"raw":2,"scal

> ed":false,"timing":false,"split24":false,"pps":true}

> 

> tcp://localhost:2947          NMEA0183>

> ┌──────────────────────────────────────────────────────────────────────────────┐

> │Time: 2017-08-06T18:33:45.000Z Lat:  12 34' 56.789" N Lon:   0 12' 34.567" E  │

> └───────────────────────────────── Cooked TPV 

> ─────────────────────────────────┘

> ┌──────────────────────────────────────────────────────────────────────────────┐

> │ GPGGA GPRMC GPVTG GPGSA GPGSV                                                │

> └───────────────────────────────── Sentences 

> ──────────────────────────────────┘

> ┌──────────────────┐┌────────────────────────────┐┌────────────────────────────┐

> │Ch PRN  Az El S/N ││Time:      183345.0         ││Time:      183345.0         │

> │ 0   1 130 42  35 ││Latitude:   1234.567890 N   ││Latitude:  1234.567890      │

> │ 1   3  52 78  40 ││Longitude:  00012.34567 E   ││Longitude: 00012.34567      │

> │ 2   9 201 22  40 ││Speed:     0.0              ││Altitude:  109.4            │

> │ 3  11 151 20  45 ││Course:                     ││Quality:   1   Sats: 10     │

> │ 4  17 257 46  25 ││Status:    A       FAA: A   ││HDOP:      0.9              │

> │ 5  19 288 41  34 ││MagVar:    0.0  E           ││Geoid:     47.0             │

> │ 6  22  77 52  39 │└─────────── RMC ────────────┘└─────────── GGA 

> ────────────┘ │ 7  23 180 50  38 │┌────────────────────────────┐┌────────────────────────────┐

> │ 8  31  59 19  26 ││Mode: A2 Sats:              ││UTC:           RMS:         │

> │ 9 120   0  0  35 ││DOP: H=0.9   V=0.8   P=1.2  ││MAJ:           MIN:         │

> │10  12 338  5   0 ││TOFF:  3535.132782450       ││ORI:           LAT:         │

> │11  14  39  9   0 ││PPS:                        ││LON:           ALT:         │

> └────── GSV ───────┘└──────── GSA + PPS ─────────┘└─────────── GST 

> ────────────┘

> (83) 

> {"class":"VERSION","release":"3.11","rev":"3.11-3","proto_major":3,"pr

> oto_minor":9}

> (125) 

> {"class":"DEVICES","devices":[{"class":"DEVICE","path":"udp://192.168.

> 13.100:10110","activated":"2017-08-06T19:31:50.526Z"}]}

> (122) 

> {"class":"WATCH","enable":true,"json":false,"nmea":false,"raw":2,"scal

> ed":false,"timing":false,"split24":false,"pps":true}

> (73) 

> $GPGGA,183345.0,1234.567890,N,00012.345678,E,1,10,0.9,9.4,M,47.0,M,,*5

> D

> (71) 

> $GPRMC,183345.0,A,1234.334342,N,00012.345678,E,0.0,,060817,0.0,E,A*24

> (34) $GPVTG,,T,0.0,M,0.0,N,0.0,K,A*0D

> (59) $GPGSA,A,2,01,03,06,09,11,17,19,22,23,31,,,1.2,0.9,0.8*31

> (70) 

> $GPGSV,3,1,12,01,42,130,35,03,78,052,40,09,22,201,40,11,20,151,45*7C

> (70) 

> $GPGSV,3,2,12,17,46,257,25,19,41,288,34,22,52,077,39,23,50,180,38*7B

> (61) $GPGSV,3,3,12,31,19,059,26,33,,,35,12,05,338,,14,09,039,*46

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