[ntp:questions] How to debug PPS?

Chaofu Chen chaofu.chen at yahoo.com
Thu Apr 22 16:22:40 UTC 2010


Hi all. I want to build a NTP server but PPS doen't work for the time being. Status bits from "ntptime" and "ntpdc -c kern" include PLL and NANO, sometimes PPSTIME and PPSFREQ, but PPSSIGNAL never appears.

------- system overview ---------------
MotherBoard: Intel Atom N270 / Intel 945GSE+ICH7M
OS: FreeBSD 7.2R, kernel recompiled with option PPS_SYNC
NTP: v4.2.6p1
PPS: -8.6v ~ +7.7v, 1Hz, pulse width 500ms
Time source: GGA sentense from GPS module, 9600bps, through cuad0
------- ntp.conf -------------
server 127.127.20.1 mode 18 prefer
fudge 127.127.20.1 flag1 1 flag2 1 flag3 1
...
-------- output of ntpq ----------------------
ntpq>pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*GPS_NMEA(1)     .GPS.            0 l   53   64  377    0.000   -4.503   8.626
ntpq>as
ind assid status  conf reach auth condition  last_event cnt
===========================================================
  1 18533  9644   yes   yes  none  sys.peer   reachable  4
ntpq>rv
associd=0 status=042d leap_none, sync_uhf_radio, 2 events, kern,
version="ntpd 4.2.6p1 at 1.2158-o Thu Apr 22 13:28:36 UTC 2010 (1)",
processor="i386", system="FreeBSD/7.2-RELEASE", leap=00, stratum=1,
precision=-18, rootdelay=0.000, rootdisp=13.349, refid=GPS,
reftime=cf7ad712.6e321a44  Thu, Apr 22 2010 22:09:22.430,
clock=cf7ad712.7f655c3a  Thu, Apr 22 2010 22:09:22.497, peer=18533, tc=6,
mintc=3, offset=-4.111, frequency=-4.879, sys_jitter=7.301,
clk_jitter=0.000, clk_wander=0.006
ntpq>cv
associd=0 status=0000 , no events, clk_unspec,
device="NMEA GPS Clock",
timecode="$GPGGA,140929,3130.8506,N,10444.6118,E,1,09,0.9,529.2,M,-32.4,M,,*60",
poll=17, noreply=0, badformat=0, baddata=0, fudgetime1=0.000, stratum=0,
refid=GPS, flags=5
---------- output of ntpdc -c kern -------
pll offset:           -0.00395776 s
pll frequency:        -4.879 ppm
maximum error:        0.032849 s
estimated error:      0.003847 s
status:               2007  pll ppsfreq ppstime nano
pll time constant:    6
precision:            1e-09 s
frequency tolerance:  496 ppm
---------- output of ntptime -----------
ntp_gettime() returns code 5 (ERROR)
  time cf7ad741.5a770bb0  Thu, Apr 22 2010 22:10:09.353, (.353379029),
  maximum error 36849 us, estimated error 3847 us, TAI offset 0
ntp_adjtime() returns code 5 (ERROR)
  modes 0x0 (),
  offset -3926.940 us, frequency -4.879 ppm, interval 1 s,
  maximum error 36849 us, estimated error 3847 us,
  status 0x2007 (PLL,PPSFREQ,PPSTIME,NANO),
  time constant 6, precision 0.001 us, tolerance 496 ppm,
---------------------------------------------------

Any suggestions or help will be appreciated.




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