On Fri, Jan 14, 2011 at 1:30 PM, unruh <[email protected]> wrote: > On 2011-01-14, Chris Albertson <[email protected]> wrote: >>> When the software (any software) only receives a PPS signal and a >>> serial message conveying the absolute time, but it does not know how >>> much the serial message is offset from the true time, how should it >>> determine the true time? >> >>>From a configuration file that describes the relationship between the >> PPS and text message. > > How in the world does whoever set up that config file know that > difference? The program can use the same algorithm you do to determine > that.
The only way to know is to compare to another reference assumed to be correct. Pool NTP servers would be accurate enough for that. The GPSes (Motorola Oncore) I use have a related "problem" in that they allow the pulse to be adjust so that it happens before the UTC second or any time during the second. So I actually have a choice. But how to set it and know it is right? What you'd do is adjust the timing until it was a best match to the other reference clocks you have or lacking that to a set of pool NTP servers I think what this proves is that setting up a Stratum One NTP server requires that you have access to multiple clocks in your lab. eBay makes this very inexpensive now. Many people have three or more clocks and test equipmnt so that they can be compared. Lacking this, it is just a gues if your server has corect time Could this be automated? Maybe, to some degree. The reference clock driver would need to have a "survey mode" setting where it would run for many hours and compare it's own time to others. NTP does this already, almost, what it lacks is a way to capture the measured offset and fold it back to a config file. -- ===== Chris Albertson Redondo Beach, California _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
