[ntp:questions] ntpd connect gpsd shared memory driver

Charles Elliott elliott.ch at verizon.net
Wed Jun 19 09:23:38 UTC 2013


You can slightly improve NTPS's performance by suppressing all the NMEA
messages except the one NTPD needs for the time, such as RMC.  That way the
program does not have to sort through the receive buffer looking for the
particular message type it needs, and there is much less traffic on the
RS-232 line.  Many GPS device manufacturers have manuals that tell how to
change the NMEA message output rate.  If you have a SiRF or SURE chip, I can
help with such a manual.

Charles Elliott

> -----Original Message-----
> From: questions-bounces+elliott.ch=verizon.net at lists.ntp.org
> [mailto:questions-bounces+elliott.ch=verizon.net at lists.ntp.org] On
> Behalf Of Richard Cagley
> Sent: Tuesday, June 18, 2013 2:16 PM
> To: A C
> Cc: questions at lists.ntp.org
> Subject: Re: [ntp:questions] ntpd connect gpsd shared memory driver
> 
> On Tue, Jun 18, 2013 at 11:06 AM, A C <agcarver+ntp at acarver.net> wrote:
> 
> > I suspect you may have a conflict between the kernel attempting to
> control
> > PPS and gpsd attempting to use it.  Try adding "disable kernel" to
> the
> > ntp.conf to shut off the kernel's use of PPS and see if that wakes up
> gpsd.
> >  If so, your serial driver doesn't want to play nice and share the
> DCD line
> > between two processes.
> 
> 
> Yeah, I agree. This definitely seems like the problem. I have pps
> support
> built into the kernel. Should I remove that support? It's slightly
> confusing to me who "controls" the pps line as there are several actors
> in
> play here...gpsd, ntpd, the kernel.
> 
> With the new entry "disable kernel" in ntpd.conf...
> ---
> server 127.127.28.0 minpoll 4 maxpoll 4
> fudge 127.127.28.0 time1 0.420 refid GPS
> server 127.127.28.1 minpoll 4 maxpoll 4 prefer
> fudge 127.127.28.1 refid GPS1
> server clock.redhat.com
> server 0.us.pool.ntp.org
> server 1.us.pool.ntp.org
> server 2.us.pool.ntp.org
> server 3.us.pool.ntp.org
> disable kernel
> ---
> I get this after about 5 min...
> ---
> / # ntpq -p
>      remote           refid      st t when poll reach   delay   offset
>  jitter
> =======================================================================
> =======
> *SHM(0)          .GPS.            0 l   14   16  177    0.000   20.062
>  12.250
>  SHM(1)          .GPS1.           0 l    -   16    0    0.000    0.000
> 0.000
>  clock1.redhat.c .CDMA.           1 u   56   64    3   81.138  -165.16
>  14.327
>  vimo.dorui.net  198.82.1.203     3 u   56   64    3   81.730  -166.40
>  14.743
>  soft-sjc-01.ser 64.250.229.100   2 u   56   64    3   12.289  -165.71
>  10.420
>  199.4.29.166    64.113.32.5      2 u   56   64    3   74.375  -162.43
>  11.199
>  66-162-15-65.li 64.236.96.53     2 u   59   64    3   64.446  -159.15
>  10.202
> ---
> _______________________________________________
> questions mailing list
> questions at lists.ntp.org
> http://lists.ntp.org/listinfo/questions



More information about the questions mailing list