> -----Original Message----- > From: questions- > [email protected] > [mailto:questions- > [email protected]] On > Behalf Of A C > Sent: Friday, December 21, 2012 3:56 PM > To: [email protected] > Subject: Re: [ntp:questions] A Christmas puzzler - intermittent > offset oscillations with a PPS source > > On 12/21/2012 11:51, Rick Jones wrote: > > David Taylor <[email protected]> wrote: > >> Although the offset appears to have a 1.25 hour period from > the MRTG > >> graphs, examining the loopstats directly shows that the > actual > >> period is just over about 5/3 minutes - just over 100 > seconds. I > >> don't know what's happening. I would have put it down to > poor GPS > >> strength, except that the effect lasts almost a whole day, > and GPS > >> missing usually contributes bigger offset spikes. I would > not > >> expect it to be the navigation mode of the GPS as the > excursions are > >> larger than I would expect between navigation and timing > modes, but > >> I don't have a lot of experience in that area. One > difference in > >> the configuration is that #1 - the one with the offsets - > runs and > >> uses gpsd for the coarse seconds, whereas #2 relies on the > rest of > >> the network. This seems to causes a higher CPU usage in #1, > shown > >> in there graphs: > > > >> http://www.satsignal.eu/mrtg/performance_raspi-1.php > >> http://www.satsignal.eu/mrtg/performance_raspi-2.php > > > > Does the gpsd do anything every 5/3 minutes? Or put another > way, can > > you find a similar periodicity in the CPU utilization? If it > does do > > something interesting at that frequency and it involves a > system call, > > while the act of tracing would perturb things, you might find > it in a > > (timestamped) system call trace (strace) of the gpsd. > > > > Perhaps the luck of process scheduling and the gpsd or some > other > > daemon holds-off the ntpd? (Raspberry Pi's are single-core > systems > > right?) Does the ntpd run at a higher (realtime?) priority > than the > > gpsd? > > > > Might there be any other background dameons consuming more CPU > on the > > one system than the other? > > > > I see something similar under NetBSD and a GlobalSat receiver > using gpsd > for coarse numbering and direct PPS via DCD into ntpd for the > PPS sync > (ATOM driver). The period of instability in my case is much > longer but > regular at something like 100 hours (there's also a smaller > spike every > 24 hours due to logrotate and similar housekeeping). I've never > tracked > down the 100 hour cycle, though. > > _______________________________________________ > questions mailing list > [email protected] > http://lists.ntp.org/listinfo/questions [Mischanko, Edward T]
Why use GPSD? I am running FreeBSD 8.2 and use the NMEA driver along with the ATOM driver. If this is incorrect, how do I use GPSD? I am very new to FreeBSD and UNIX in general, so your patience is appreciated. Regards, Ed _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
