Re: [chrony-users] gpsd, pps and chrony

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Mon, 4 Apr 2011, Ed W wrote:

> Hi
>
> > Since an NMEA ntp client is a stratum 1 and since NMEA has an accuracy
> > around
> > 10ms (yes, ms, not us) there is no such requirement. Ie, the accuracy of
> > stratum 1 clocks varies wildly.
>
> By implication are you suggesting that you expect a decent proportion of
> current pool.ntp.org stratum 1 servers are only synced to within some
> few ms of "correct"?  Seems a bit sad?

I have no idea what proportion. All I am saying is that you should not rely on
the pool if you want to have guarenteed good time. In fact I have seen some
comments where memebers of the pool were out by days, or even years. If you
use enough sources and if you are not terribly unlucky, those should not
affect your time.

> There is some info on the ntp.org wiki where servers can volunteer their
> hardware setup info.  Quite a few suggest using decent hardware?

Of course.

> I presume it's somewhat moot in that you are bounded by the limits of
> the various tcp connections, but still seems like the tech is easily
> available and we ought to be trying to get current stratum 1 time
> servers to be syncing within some few 10s of usecs?

It is a volunteer system. Unless Mills wants to spend his time testing all of
the pool servers, it will stay that way.

> > > Incidently, while we are geeking out on chipsets, I saw Skytraq
> > > mentioned on the gpsd mailing list and they do all kinds of fun stuff,
> > > some with fairly inexpensive eval boards, this has 30ns PPS pecision:
> > >    http://www.skytraq.com.tw/news20090701.htm
> >
> > Remember that the sure board includes usb ( ie power supply) and antenna in
> > its $30 price.
>
> Hmm, cool.  Note that I haven't found a supplier doing a simple eval
> board for the time sync clock above, but other eval boards with similar
> chipsets are going for only a little more than the Sure board (without
> antenna though).  They are also generally much smaller boards? Certainly
> similar enough that shipping costs will determine which is cheapest.

I looked at one where the board was $60. With powersupply and antenna it was
$190.

> Cool that very decent GPS chipsets are getting plentiful at very
> sensible prices.
>
>
> > > (They also have a 20hz GPS with decent sensitivity and a GPS/GLONASS
> > > hybrid board...)
> >
> > And exactly what would a 20Hz buy you?
>
> :-)
>
> Perhaps you want to track your guided rocket?
>
> Actually given that they only appear to be the same kind of pricing as
> any other GPS board, if you were into UAVs it could be very handy.  I
> guess also anyone tracking "racing" things would also like one?
>
> Cheers
>
> Ed W
>
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--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
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