[ntp:questions] PPS as a falseticker!!!

valizadeh65 at gmail.com valizadeh65 at gmail.com
Wed Aug 27 09:48:48 UTC 2014


Following my previous post.
https://groups.google.com/forum/#!topic/comp.protocols.time.ntp/aGjxoHvj0QA

I not sure, how should I write the ntp.conf file to achieve the maximum accuracy using pps. 
i don't know  if the ntpd use the pps or not in my case! 
Sometimes it is recognized as a "falseticker" (x) and sometimes it is OK(o) !!!

I tested different ntp.conf and here are some results (ntp.conf and ntpq-p):

#TEST:1

 ----- ntp.conf-------
server 127.127.22.1 minpoll 4 #PPS
server 127.127.20.1  prefer minpoll 4 mode 16 #GPS
fudge 127.127.20.1 flag1 1 flag3 1
-----
GPS on COM port (PPS connected to DCD pin)
remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
xPPS(1)          .PPS.            0 l    3   16  377    0.000   30.681  29.011
oGPS_NMEA(1)     .GPS.            0 l    2   16  377    0.000   29.964  29.404

|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

#TEST:2 

----- ntp.conf-------
#server 127.127.22.1 minpoll 4 #PPS
server 127.127.20.1  prefer minpoll 4 mode 16 #GPS
fudge 127.127.20.1 flag1 1 flag3 1
GPS on COM port (PPS connected to DCD pin)
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
oGPS_NMEA(1)     .GPS.            0 l    -   16  377    0.000   -1.004   0.316


Questions:
1-	Shall the  "server 127.127.22.1 minpoll 4 " be inevitably present in ntp.conf?(test1) or can driver 20 use the PPS individually  by enabling flag1 1(test2)
2-	How can kernel pps discipline affect the time sync accuracy? What do you recommend? Enable or disable it?
3-	What are the best choices for flag 1, flag 2, flag 3 in driver20 and 22?
4-	How may I select the best time1, time 2 in driver 20 and 22? Shall I use the oscilloscope? What should I measure? 



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