Joachim, Thanks for your detailed solution, which was along the lines of my thinking..
Do you know of any off-the-shelf GPS receiver with RS232 and PPS capability? Hal, >> What sort of distance accuracy are you expecting? Not very stringent..up to 10m will do. >> What sort of distances will you be operating over? 50m - 1000m >> How unreliable is your link? Very. The packet error rate can vary between 0 - 100%. >> I would ignore NTP and do everything yourself. >> >> Do something like ping. That takes 2 packets, but you don't need to know the >> time on the other end. If both ends need to know the distance, you can make >> a measurement with 3 packets. >> >> Or you can send a dozen packets and use the minimum time assuming the others >> had delays in the interrupt handler. (and use the spread in the times as an >> indication of quality) >> >> You will probably need to calibrate the response times of the CPUs and the >> delays through the radios so you can subtract it out. The radio delays may >> may depend on signal strength which varies with distance, but will also >> change if you go behind mountains or trees or buildings. Interesting technique, but for One way delay measurements, it will introduce a lot of measurement error, particularly as the links are unreliable and asymmetric (uneven delays). Best, Sandip On Mon, Sep 14, 2015 at 1:40 PM, Joachim Fabini <joachim.fab...@tuwien.ac.at > wrote: > On 14.09.2015 12:43, Hal Murray wrote: > > > Joachim Fabini said: > >> - Re-compile your kernel for LinuxPPS support, following the > instructions on > >> http://linuxpps.org/wiki/index.php/LinuxPPS_installation . > > > > That hasn't been necessary for a long long time. > > Most recent distributions have PPS line support enabled by default. > Still, kernel build is necessary if you have special driver requirements > or change options - I recompile measurement kernels for increasing the > Hz rate. The page contains some outdated information but some of it is > valuable (in particular the reference to the ppstools repository and > timepps.h copy that is essential for building ntp). > > > What version of the kernel are you using? > > 3.8 - 3.13 > > > Recent kernels need something like: > > ldattach 18 /dev/ttyS0 > > which creates /dev/pps0 > > Yes, that's what I do. Ideally you can automate it and trigger some > additional ntp prerequisites (udev-related) as recommended on the ntp > pps support page (http://linuxpps.org/wiki/index.php/LinuxPPS_NTPD_support > ) > > > > _______________________________________________ > questions mailing list > questions@lists.ntp.org > http://lists.ntp.org/listinfo/questions > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
