Unruh schrieb: > [EMAIL PROTECTED] (Nicola Berndt) writes: > >> Hello, > >> recently I tried building a microsecond precision timeserver using a >> gps-device with pps signal. > >> The gps-data is transmitted via usb, the pps signal via the rs232 >> carrier detect line. > >> I tried several drivers and they all worked, but I had to figure that >> obviously my mainboard (via epia en12000EG) has terrible jitter. - unusable! > > Are you sure that it is not the reading of the time that is the problem. > What gps do you use? Are you sure it really has and is using PPS? > And what do you call "terrible" >
I use a Conrad USB-Receiver that contains a U-Blox board. I took the PPS-Signal from the according pins inside the device myself and tested, if it sends a pulse every second and it does. So that looks ok to me. "Terrible" I call that I can watch the jitter with ntpq -p jump from -50 to 50. I assume those are microseconds, so +/-50 ms makes 1/10 seconds. I can set any clock that precise using my bare hands ;) The next problem I actually stumbled across is the long time ntpd needs to settle. The system I inted to build has to be ready right after the start, because the pc lies in a shelf, off, and is switched on right when needed. There is no way to let it run, since it is battery-driven. > > >> To solve the problem I think about simply setting the time every n >> seconds according to the collected gps time and the pps-signal. My >> system will run off for far less than a microsecond in an interval of >> let's say, 20 seconds or so. Like this I would implement a constantly >> jumping time, but the amount of jumps would be extremely small. > > Just use ntp to discipline your clock. No need to try to bacly reinvent > something. Oh, I happily would, I just didn't get it to work and gave up at some point (after days..) best regards, ../nico _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
