On Feb 27, 2010, at 2:25 PM, Goran Sandin wrote: > Hi, > > I have built a ntp-server based on information found > here http://www.febo.com/pages/soekris/ and here > http://ralphsmith.org/~ralph/soekris-ntp/NET4501.
First of all, a caution that the files under <http://ralphsmith.org/~ralph/soekris-ntp/> were placed there at various times and are not part of a coherent whole. I really need to clean this up and put together a unified treatment. > > I use this tool http://www.satsignal.eu/software/net.htm#NTPmonitor to check > the result. > > The result is not in line with my expectations so I think something is not > quite right. > > If I compare with a normal PC (running FreeBSD 7.1) which is synchronized > against stratum 2 servers over Internet, the performance I get from net4501 > is > not any better than this PC. > > The NTPmonitor program show following result: > > An Internet Stratum1 server | my PC | net4501 > > Precision: 2^-29s 2^-19s 2^-16s > > Dispersion: 2ms ~30ms 0ms The precision values shown are to be expected, and isn't anything to really get excited about, and is a function of the machine architecture. From <http://www.ntp.org/ntpfaq/NTP-s-sw-clocks-quality.htm> we read "In NTP precision is determined automatically, and it is measured as a power of two. For example when ntpq -c rl prints precision=-16, the precision is about 15 microseconds (2^-16 s)." > > > Both the PC and net4501 show a huge offset error of 1s about 11 times in 2 > hours. The Internet Stratum1 server does not seem to have this error. Can't help much until we know what peers and refclocks you have configured. Also, make sure that you have the following in your kernel configuration. options CPU_ELAN options CPU_SOEKRIS options HZ=150 options CPU_ELAN_PPS > > My feeling is that my net4501 server does not really use the PPS signal. > How do I check if the ntpd daemon actually use the PPS? What are you using to drive the PPS signal? ntpq -p will tell you if ntp is using the pps. This all depends on course on what drivers you configure it to use: my system is currently showing: wendell# ntpq -p remote refid st t when poll reach delay offset jitter ============================================================================== +ntp.cox.net .GPS. 1 u 1594 1024 366 28.771 2.371 0.545 *SHM(0) .GPS. 0 l 15 16 377 0.000 4.976 0.231 oPPS(0) .PPS. 0 l 12 16 377 0.000 0.000 0.015 wendell# The "o" in the first column tells me that ntp is synchronizing with the PPS. Offset is less than 1 microsecond. > > Or rather, how do I know the the precision of the PPS signal is transferred > into the ntpd daemon? > > (I can see with ntpq -p that the PPS row from the config file is selected) Showing what ntpq -p gives you would help. > The description on febo.com says that the PPS signal should be supplied at > R61/R62. I have made this as well as JP3, pin3. Does anyone know where > R61/R62 > is connected, why is this needed as well as on the GPIO pins? I just followed > the instruction, but it is hard to do fault finding when not knowing the idea > behind it from the beginning :-) R61/R62 is connected to TMR1IN on the ElanSC520, which is not otherwise available to the outside of the Net4501. Read elan-mmcr.c for an explanation of how the precise time stamping is done, but in short, you need the signal at both locations in order for this to work. > On http://ralphsmith.org/~ralph/soekris-ntp/NET4501, there are a set of gpsd > files. I could not find anything about how to start the gpsd so I have not > installed it, don't know if it is needed or not? That depends on what you are trying to use as a reference. I used gpsd as a driver for my Trimble Thunderbolt, until I wrote tboltd, a much simpler program, but added a few features I need. What is your reference clock? Ralph _______________________________________________ Soekris-tech mailing list Soekris-tech@lists.soekris.com http://lists.soekris.com/mailman/listinfo/soekris-tech
