As you can see it starts out with an offset of about .02 sec, which decreases
to about 0 sec. Ie, offsets can easily change. At a certain point you simply
cannot improve things with the offset adjustment. You just have to be happy
with what you have.

Not sure what you want.

Note that if the clock is driven only with the GPS signal, then its will
wander around from "true" time by hundredths of a second.




William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ un...@physics.ubc.ca
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/

On Fri, 19 Aug 2016, Chris Greenman wrote:

Finally got a chance to grab more stats.    my refclock line now looks like
this:
refclock SHM 0 refid GPS offset 0.060 delay 0.22 minsamples 64


I'm attaching the latest stats.

On Mon, Aug 15, 2016 at 10:18 AM, Bill Unruh <un...@physics.ubc.ca> wrote:
      On Mon, 15 Aug 2016, Chris Greenman wrote:


            No. We're just fine tuning the refclock line in
            chrony.conf.  I don't really
            experience huge jumps.  It might fall behind during a
            reboot because the pi doesn't
            have an RTC but rather it saves time on shutdown and
            restores on boot.


      Ah sorry. they yes, during that time period gps settled down to
      being out about 10ms
      which is well within your requirements. Unrotunately, nmea is not
      the most
      stable of references. Thus if for some reason your gps puck
      becomes busy for
      some reason, (moving the computer, something happens with the gps
      constellation,...) that offset could change, but certainly not by
      a second.
      The handling of leap seconds by your puck could be an issue. Not
      sure how it
      handles that. But at worst it would mean that some midnight (UTC)
      at the end
      of Dec or Jun, the clock would suddenly be out by a second, and
      would slowly
      (well not that slowly with chrony) drift its way back into sync.





            Really my only goal is to have somewhat accurate
            (less than a second) time whether I
            have internet or not.   We've already achieved this,
            now it's just a matter of
            making sure GPS doesn't clobber ntp and vice versa.


      Not sure what you mean by "ntp".



            On Aug 14, 2016 7:24 PM, "Bill Unruh"
            <un...@physics.ubc.ca> wrote:
                  Is this supposed to be at a time when your
            system suddenly looses track
                  of the
                  time and jumps by hours or days? I see nothing
            in the gps signal that
                  indicates anything like that.

                  If it is supposed to be at the begining of this
            sample, please give a
                  sample
                  which spans across, not begins at, one of those
            weirdnesses.

                  Note also that probably a copy of the
            measurements and the refclock logs
                  ove
                  onw of those times might be more illuminating.
            Statistics is rather
                  processed
                  already.






                  William G. Unruh __| Canadian Institute
            for|____ Tel: +1(604)822-3273
                  Physics&Astronomy _|___ Advanced Research
            _|____ Fax: +1(604)822-5324
                  UBC, Vancouver,BC _|_ Program in Cosmology
            |____ un...@physics.ubc.ca
                  Canada V6T 1Z1 ____|____ and Gravity ______|_
            www.theory.physics.ubc.ca/

                  On Sun, 14 Aug 2016, Chris Greenman wrote:

                        Ok  I grabbed a sample of the clock
            statistics.  


                        On Fri, Aug 12, 2016 at 2:53 PM, Bill
            Unruh
                        <un...@physics.ubc.ca> wrote:
                              On Fri, 12 Aug 2016, Chris Greenman
            wrote:

                                    it's a usb puck.  so no. 
            Actually I haven't
                        actually looked but
                                    typical USB is +5v data+
            data- and gnd.  As
                                    far as I know the only place
            the pps signal is
                        available is inside the
                                    puck between the GPS module
            and the usb
                                    interface.  


                              Well, usb serial immitatiors can
            also immitate the
                        control lines from a serial
                              line. Thus one of the usb packets
                        of the PPS signalalong
                              the appropriate serial line.  But
            those are likely to
                        have far worse behaviour
                              than the actual lines.
                              It might however be better than the
            data phrases
                        usually coming along the
                              serial line.



                                     like I said I COULD crack it
            open and run a new
                        cable that included
                                    the pps line.

                                    On Fri, Aug 12, 2016 at 2:24
            PM, Bill Unruh
                        <un...@physics.ubc.ca>
                                    wrote:


                                          William G. Unruh __|
            Canadian Institute
                        for|____ Tel:
                                    +1(604)822-3273
                                          Physics&Astronomy _|___
            Advanced Research
                        _|____ Fax:
                                    +1(604)822-5324
                                          UBC, Vancouver,BC _|_
            Program in Cosmology
                        |____
                                    un...@physics.ubc.ca
                                          Canada V6T 1Z1
            ____|____ and Gravity
                        ______|_
                                    www.theory.physics.ubc.ca/

                                          On Fri, 12 Aug 2016,
            Chris Greenman wrote:

                                                I CAN hook it up
            for PPS but it will
                        require cracking open
                                    the puck and it's not that
                                                crucial for my
            use
                                                anyway.  


                                          Isn't there an output
            line from the puck
                        which carries the PPS
                                    signal?








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