[ntp:questions] what happens when sys.peer turns stratum 16?

Rob nomail at example.com
Wed Jun 2 08:20:16 UTC 2010


Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:
> In article <884d589f-378f-4568-a641-003c6bea925e at d12g2000vbr.googlegroups.com>,
>  pc <Paul.Croome at softwareag.com> writes:
>>The Motorola Oncore UT GPS receiver, which was designed as a precision
>>time source, has a T-RAIM (time receiver autonomous integrity
>>monitoring)
>>feature which, properly configured, switches off the PPS output if
>>the receiver loses lock.
>
> But lots of low-cost GPS receivers don't do that.
>
> And there is the "properly configured" constraint.  If you
> have a good antenna position you might not notice that you
> are still getting a PPS when you don't want it because that
> case doesn't get tested often enough to notice any problems.

Ok but who would ever think of the insane idea to get a GPS receiver
and connect only its PPS output to a computer, and let NTP sync from
that?
Not only would it be unable to get correct time outside of the +/- 500ms
interval that a PPS would be able to correct, but you would also be
trusting a signal without having any information whether it can be
trusted.
I cannot understand how anyone would create a setup like that and would
think it was any good...  you can just as well build a freerunning
oscillator of 1 Hz and sync to that.

OF COURSE you also need to connect the serial stream from the GPS
receiver, and the driver needs to evaluate the messages to enable/disable
the PPS lock depending on the GPS lock information in the messages.

Do you know of any driver in use that does not do that?




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