[Linuxpps] Duplicated sequence numbers

[Adam James]

Hello,

I have a Garmin GPS25-LVC configured to output a 100ms PPS pulse and
the standard NMEA sentences. Rodolfo's LinuxPPS implementation seemed
much neater than the SHMPPS driver I am using at the moment, so I
thought I'd give it a try. 

While it does seem to be working, the jitter and offset are much
higher than when I was running the SHMPPS driver. Can anyone show me
some graphs or `ntpq -p' output to show what they have achieved using
the current implentation?

Perhaps you could also advise as to whether the following ppstest
output is a bug or a problem with my system (notice the duplicated
sequence numbers):

# ./ppstest
found PPS source #0 "pps_8250_0" on "/dev/ttyS0"
Assert timestamp: 1148936547.001043675, sequence: 2285
Assert timestamp: 1148936547.001043675, sequence: 2285
Assert timestamp: 1148936548.001042675, sequence: 2286
Assert timestamp: 1148936548.001042675, sequence: 2286
Assert timestamp: 1148936549.001045675, sequence: 2287
Assert timestamp: 1148936549.001045675, sequence: 2287

I'm running a patched 2.6.16.7 kernel and ntpd
4.2.0a at 1:4.2.0a+stable-8-r (patches taken from
http://time.qnan.org/linux2.6-pps/).

dmesg output:

May 29 21:10:40 evolution kernel: "pps_core": procfs enabled
May 29 21:10:40 evolution kernel: "pps_core": LinuxPPS API ver. 1 registered May 29 21:10:40 evolution kernel: "pps_core": Software ver. 2.0.0 - Copyright 2005-2006 Rodolfo Giometti <giometti at linux.it>

ntpd output:

May 29 21:25:07 evolution ntpd[4247]: refclock_nmea: time_pps_kcbind failed: Operation not supported
May 29 21:25:07 evolution ntpd[4247]: refclock: found PPS source #0 "/dev/ttyS0" on "pps_8250_0"

# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
-GPS_NMEA(0)     .GPS.            0 l    7   16  377    0.000   -1.057   0.028
-ntp0.zen.co.uk  195.66.241.3     2 u   55  128  377   14.765    4.265   0.483
+veracity.mcc.ac 193.62.22.98     2 u  122  128  377   14.960   -0.274   0.533
*ntp0.ja.net     .MSF.            1 u   55  128  377   20.725    0.016   0.173
-ntp1.linx.net   .1PPS.           1 u   48  128  377   26.675   -0.715   0.824
+tt01.ripe.net   .GPS.            1 u   52  128  377   29.484   -0.052   0.372
 LOCAL(0)        LOCAL(0)        10 l   58   64  377    0.000    0.000   0.001

Relevant ntp.conf data:

server 127.127.20.0 minpoll 4 maxpoll 4
fudge 127.127.20.0 flag2 0 flag3 1 time1 0.00

Any advice would be appreciated.

--Adam