[LinuxPPS] Need help with setting up LinuxPPS/NTP server

[Hal V. Engel]

On Wednesday 08 October 2008 09:52:54 Richard Abbott wrote:
> Hello all. I am having a bit of trouble getting a system configured to
> pull time and PPS from my GPS unit. I think I am close but I'm not sure
> where the disconnect in my system or configuration is and am hoping that
> y'all will be able to help me.
>
> I have followed the instructions on these sites as best I could and am
> seeing (more or less) what they say I am supposed to be seeing.
>
> http://time.qnan.org/
> and
> http://wiki.enneenne.com/index.php/LinuxPPS_support
>
> I am using a Garmin 35LVC for my OEM GPS unit. I have patched and
> compiled the 2.6.26 kernel with the appropriate LinuxPPS patch and have
> patched and compiled ntp-4.2.4p2 with the NMEA patch. For the kernel I
> have built in the 8250 serial and PPS directly into the kernel instead
> of as modules. RHEL4 update 5 AS standard install is the rest of the
> platform.
>
> The ntpd server is communicating with the GPS device but I suspect that
> it is not receiving the PPS signals. When ntpq is run it shows very
> large offset and jitter values when compared to servers it is connected
> to over the internet for comparison.
>
> Here are the config files as they are running on my machine and output
> from logs. Please let me know if there is other info that you would like.
>
> After booting I have to manually create symlinks /dev/gps0 -->
> /dev/ttyS0 and /dev/ppsgps0 --> /dev/pps0
>
>  > dmesg | grep 8250
>
> Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing enabled
> serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
> serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
>
>  > dmesg
>
> .......
> PPS event at 56274
> PPS event on source 0 at 1223477791.159246144
> PPS event at 56524
> PPS event on source 0 at 1223477792.159245962
> PPS event at 56774
> PPS event on source 0 at 1223477793.159244902
>
>  > cu -l /dev/ttyS0 -s 4800
>
> .......
> $GPRMC,145903,A,3022.9421,N,09744.6923,W,000.0,340.9,081008,005.8,E*61
> $GPGGA,145903,3022.9421,N,09744.6923,W,1,10,1.9,275.3,M,-23.1,M,,*70
> $GPGSA,A,3,03,,07,13,16,19,20,23,25,27,32,,3.3,1.9,2.6*37
> $GPGSV,3,1,11,03,48,100,36,06,40,080,30,07,34,304,38,13,62,325,36*72
> $GPGSV,3,2,11,16,24,041,30,19,36,142,33,20,19,200,31,23,85,133,40*76
> $GPGSV,3,3,11,25,48,325,35,27,26,300,33,32,09,181,31,,,,*40
>
>  > cat /sys/class/pps/pps0/assert
>
> 1223478098.159245740#827
>
>  > cat /sys/class/pps/pps0/assert
>
> 1223478100.159250016#829
>
>  > tail /var/log/messages
>
> Oct  8 15:02:57 localhost kernel: PPS event at 153024
> Oct  8 15:02:58 localhost kernel: PPS event at 153274
> Oct  8 15:02:59 localhost kernel: PPS event at 153524
> Oct  8 15:03:00 localhost kernel: PPS event at 153774
> Oct  8 15:03:01 localhost kernel: PPS event at 154024
>
> ntp.conf
> --------------------
> restrict default nomodify notrap noquery
> restrict 127.0.0.1
>
> # LinuxPPS: GPS + PPS
> server 127.127.20.0 prefer minpoll 4
> fudge 127.127.20.0 flag3 1 flag2 0 time1 0.0
>
> server 0.us.pool.ntp.org
> server 1.us.pool.ntp.org
> server 2.us.pool.ntp.org
>
> server  127.127.1.0     # local clock
> fudge   127.127.1.0 stratum 10
>
> driftfile /var/lib/ntp/drift
> broadcastdelay  0.008
>
>  >ntpd -g
>  >ntpq -p
>
>      remote               refid                    st t when poll
> reach   delay   offset  jitter
> ===========================================================================
>=== xGPS_NMEA(0)   .GPS.                  0 l   17   16  376    0.000
> -641.83  72.089
> +ntp2.your.org       64.202.112.65    3 u   48   64  377   29.920
> 8.623   0.722
> *rrcs-64-183-55- .GPS.                   1 u   63   64  377   66.258
> -2.181   1.880
> +mercury.element  128.252.19.1       2 u   33   64  377   42.065
> 6.104   1.858
>  LOCAL(0)           .LOCL.               10 l   40   64  377    0.000
> 0.000   0.001
>
>  > ntpdc -c kern
>
> pll offset:           0.005085 s
> pll frequency:        63.751 ppm
> maximum error:        0.239794 s
> estimated error:      0.000879 s
> status:               0001  pll
> pll time constant:    6
> precision:            1e-06 s
> frequency tolerance:  500 ppm
>
>  From the ntpq -p you can see that the ntp daemon says the GPS is being
> designated a flasticker and not being used. I do not know what is
> causing this.
>
> Any help you could provide or resources you could point me to would be
> appreciated.
>
> Thanks


First some basics.  The first thing you need to do is make sure that the pps 
signals are actually working.   

You don't have anything about running ppsldisc.  Are you running it?

Do you have the timer kernal module loaded?  If you do you should unload it to 
prevent confusion about your PPS signals.

After unloading the timer kernel module and starting ppsldisc in a separate 
terminal session what results to you get when running ppstest against your pps 
device?

Until the above is working correctly it makes no sense to try to get ntpd 
working.

Hal