Dave, When introducing our CDMA technology, EndRun thought it wise to make the initial product emulate existing hardware that had already been interfaced to unix machines via the serial port and "gadget boxes." The CDMA engine which is inside both the Ct and your Cntp emulates both the Truetime and Spectracom time strings, with 1PPS on DCD. In addition, it emulates the Trimble Palisade event capture mode on the CTS input, with 30 ns resolution. One benefit to this driver is high resolution capability on the Windows platform, another is not needing to mess with kernels that don't natively support high-resolution 1PPS timetagging.
Users of the Ct can choose the emulation mode they like and use the standard drivers in the stock ntp distribution. However, all of our ntp servers operate the CDMA or GPS engine in the CTS event capture mode with a heavily customized refclock driver. While developing our first generation ntp servers (your Cntp is one of these) using off the shelf X86 embedded single board computers running linux, we found that longer poll intervals definitely exposed the instabilities of the uncompensated crystals used on these boards. We found that with high measurement precision and holding the poll interval at 16 seconds, one microsecond level offset control could be maintained reliably, and have never experienced any loop damping issues. Our current products contain our own purpose-built X86 core with clocks that are hardware phase locked to the main system disciplined oscillator, which could be TCXO, OCXO or Rubidium. In these units, a shorter polling interval is really only an issue at startup for more rapid ntp lock because the kernel clock is rock solid between polls. Bruce Penrod David L. Mills wrote: > Kevin, > > Strange. I have an EndRun Cntp, bu it has an Ethernet interface. If 4 > works for you use it. That's a pretty grotty driver with all kinds of > bandaids to deal with long forgotten radios; I wonder why EndRun chose > that driver... > > Dave > > Kevin Oberman wrote: >> Dave, >> >> Thanks for the quick response, but I guess I failed to make one point >> clear. >> EndRun supplies only the hardware. It is the Ct which as only a serial >> interface which is plugged into a standard COM port on the server. They >> don't provide any software at all. The clock just provides the time >> string every second (with an offset of about 10 ms. and jitter in the >> area of 3-5 ms.) and a very accurate PPS which allows us sync within >> about three usec. (The clock spec is better than ten usec, but three >> seems the norm.) >> >> I am running 4.2.0-a using the stock TrueTime and PPS drivers. The >> FreeBSD kernel has PPS support included, so any filtering in the >> TrueTime driver should be of little or no impact. >> >> I am assuming than as long as I am using PPS and training the TrueTime >> source, a minpoll of 4 is reasonable and I just wanted to make sure that >> I am not wrong in doing this. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
