[ntp:questions] Type 28 driver (gpsd, SHM) - understanding "flag1"

Mike Cook michael.cook at sfr.fr
Sat Feb 21 08:33:50 UTC 2015



> Le 21 févr. 2015 à 08:37, David Taylor <david-taylor at blueyonder.co.uk.invalid> a écrit :
> 
> Folks,
> 
> I'm looking at:
> 
>  http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver28.html
> 
> and wanting to be sure that I understand flag1 correctly.  The situation is starting a computer which has no real-time clock, and has been down for a day.  This computer is in the middle of nowhere, and has a GPS and PPS as reference clocks, using the type 22 and type 28 drivers.  By observation, the type 22 (PPS) driver won't kick in until the type 28 (SHM/gpsd) driver is valid, but also by observation with no flags set it seems that the type 28 driver never syncs at all, even though valid GPS data is present.
> 
> My reading of that page is:
> 
> - the default, flag1 = 0 or absent, and no time2 set, NTP will not kick in unless the local clock is within 4 hours of the GPS time.  It seems that even with -g as an ntpd parameter, which /should/ allow a large initial offset NTP won't kick in.  In the computer in question, the difference is likely to be in excess of 24 hours, so NTP will not attempt to correct the clock.  This is not the desired behaviour!
> 
> Is my understanding correct?  Would the correct thing to do in such circumstances be to set flag1 = 1 so that the difference limit is ignored?
> 
   My aged understanding concurs with yours. Set flag 1. Maybe not your desired behavior, but possibly that of the designer.

> I ask what may be an obvious question as I appear to have difficulty in reading the page.  Perhaps old age, I hope nothing more!  I suppose I had expect the "-g" to override other sanity checks.
> 
> -- 
> Thanks,
> David
> Web: http://www.satsignal.eu
> 
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