This is a different sort of question than what seems to be discussed here usually, and I apologize if it's wholly off-topic, but I'm guessing there are some time nuts here who might be able to give me some pointers.
If I have two boxes with clocks that are supposed to be perfectly synchronized, and I need to verify this, and they're physically right next to each other, and they both have PPS outputs, one way to verify the synchronization would be to compare the two PPS outputs with a 'scope. (I'm guessing there's probably a dedicated instrument out there specialized for the task of comparing two such PPS signals for frequency, phase and jitter, and if I were a proper time nut myself I guess I'd know that.) My specific question concerns the case that one of the boxes is a computer, for example, a Linux box with time kept using ntpd or chrony (perhaps also listening to a PPS signal coming in on a serial port). But I've never seen a computer with a PPS *output*. Is this a reasonable thing to be thinking about, or am I going about it wrong? How would *you* positively verify synchronization of such a system? Me, I'm pursuing this idea because too much of the time (at least in my own, perhaps parochial experience) synchronization seems to be "verified" either by saying "Yes, we configured it properly", or by observing a status output from ntpd or chrony claiming the requisite synchronization has been achieved, but in neither case by making a definitive, independent, external, empirical determination. (Perhaps PPS is overkill for this situation; perhaps it's the case that given the inherent inaccuracies of software-based timekeeping, a software-based query mechanism -- perhaps using ordinary NTP or PTP protocols -- would be sufficient for externally assessing synchronization.) I guess it's not a *completely* unreasonable thing to be thinking about, because I've found a couple of web pages (for example https://www.raspberrypi.org/forums/viewtopic.php?t=115554 and https://github.com/jsln/pps-gen-gpio) describing how to implement a PPS output under Linux. And I do realize that trying to minimize the jitter and latency in this situation (given that the principal drivers for the hypothetical output are inherently software-based) presents considerable difficulties. But taking all of that into consideration, I'm wondering what others think of the approach. Thanks for any comments. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
