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

[Richard Abbott]

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

-- 
--
Richard Abbott <rabbott at ticom-geo.com>
TICOM Geomatics, Inc.
9130 Jollyville Rd, Ste 300
Austin, TX 78759
Office : (512)610-8340
Fax : (512)345-9992
Cell : (512)422-2352