[LinuxPPS] GPS PPS source shift back

[admin at ifconfig.com.ua]

Hi folks!

I build NTP server stratum 1

On FreeBSD this is not a problem, but on Linux a have one

I  read  all  internet,  for search how to solve my problem, but i not
found approach.

I  buy  GPS GlobalSat MR-350PS4, this GPS has PPS signal and connector
RS232.
My system Slackware Linux 14.1 X86_64, kernel build with PPS.
NTPd build with PPS support.

Kernel (build it itself) :
Linux router 3.18.21 #1 SMP Wed Sep 9 11:03:22 EEST 2015 x86_64 Intel(R) Atom(TM) CPU D525   @ 1.80GHz GenuineIntel GNU/Linux

Motherboard:
Asrock AD525PV3 (Mini-ITX Intel Atom)

Run this, and i have very large offset, GPS source (using NMEA and PPS
from 20 driver).
GPS-Nmea  spurce  lag  to  100  villisecond  each  second, after large
offset, ntpd fix offset (spike_detect) and gps source again lag.

I switch off FIFO buffer on Searial port (setserial low_latancy).


----------------------------------------------------------------------
in dmesg:
[    1.281439] pps pps0: new PPS source ktimer
[    1.289469] pps pps0: ktimer PPS source registered

----------------------------------------------------------------------

ntpq -pn :

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
xrelay2.litkk.co .GPS.            1 s    2   16  377    0.453   76.533  25.354
xGPS_NMEA(0)     .GPS.            0 l    9   16  377    0.000  -484.82 139.323

----------------------------------------------------------------------

ppstest /dev/pps0 :
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1441903282.745826269, sequence: 1478 - clear  0.000000000, sequence: 0
source 0 - assert 1441903283.747825473, sequence: 1479 - clear  0.000000000, sequence: 0
source 0 - assert 1441903284.749825802, sequence: 1480 - clear  0.000000000, sequence: 0
source 0 - assert 1441903285.751825796, sequence: 1481 - clear  0.000000000, sequence: 0
  
----------------------------------------------------------------------

And  please  explain  what  is  ldattach,  because  without this daemon
nothing changed.

Please help, what is can make this lag.
Lag  not  constant  and  variables time1 and time2 not help with this,
offset shift continuously.

Oleg A. Deordiev
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