[ntp:questions] How to debug PPS?

Dave Baxter spam at goes.nowhere.com
Fri Apr 30 07:39:35 UTC 2010


In article <90005.53446.qm at web45014.mail.sp1.yahoo.com>, 
chaofu.chen at yahoo.com says...
> 
> 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

Hi.

There was a thread on here recently, that seemed to settle on the fact 
that some implementations of NTPD do NOT work well with 9600bd NMEA data 
from the GPS.  Though to my eyes, it looks like something is seeing the 
data stream.

You could try reconfiguring the GPS so it works at the more usual 4800bd 
for the NMEA data, as well as the PPS signal of course, and see if that 
helps things.

You dont (that I've seen) say what the make/model of GPS is you have.  
It may worth configuring it (if it can be done) so it only sends $GPRMC 
sentences at 4800 baud, as well as the PPS signal..  

Just idea's from my limited experience while still experimenting with 
all this.

Best Regards, (with tin hat ready)

Dave B.
(There are too may Dave's on this list, perhaps we should all call each 
other Bruce?  With appologies to non Monty Python types.....)




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