"Richard B. Gilbert" <[email protected]> writes: >Terje Mathisen wrote: >> [email protected] wrote: >>> On Jan 19, 10:26 pm, Terje Mathisen <[email protected]> >>> wrote: >>>> [email protected] wrote: >>>>> Hello everybody, >>>>> I'm trying to track (offline) the drift of my gps clock relative to my >>>>> hw clock (the clock that I would have obtained without GPS). >>>>> My final goal is to convert a series of gps timestamps to the >>>>> equivalent hw timestamps (with microsec precision). >> >> You can get us precision but not accuracy! >> >>>> This is actually quite easy: >>>> >>>> Just enable logging of the loop frequency (i.e. the freq offset), and >>>> integrate that value over time. >>>> >>>> This gives you the offset at any given time. >>> >>> Smart, >>> your method uses the SW clock not the HW clock >>> (which eliminates the problem of the 11 mn mode) >>> >>> But what I do not understand is why are integrating frequency (f)?. >>> It would be easier to add the clock offset (o) (i agrre that the >>> result should be the same)? >> >> The clock offset will always tend to zero, that is after all exactly >> what NTP is working so hard to achieve! >> >> Running with logging a GPS which isn't used to steer the clock is >> actually much easier and more accurate. >> >> You'll find that you don't need us precision: After a few hours the >> offsets will probably be into the multiple seconds range, and go off >> from that.
>Errrr. . . . Did you have a little slip of the mind there? Offsets in >multiple SECONDS?????? Mine generally range in the multiple >MILLISECONDS! And not a very large multiple either! IF you are disciplining your clock with ntp. If you do not, you will soon find you are out by seconds, not milliseconds. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
