On 2014-01-14 09:51, Roger Oberholtzer wrote:
Our main question is how the system acts if, at boot, there is no GPS data. Is the time left alone? When the time does arrive, how quickly will the system clock reflect the time? For example, it may turn out that the PC clock and the GPS time differ by some hours. Does NTP always do a gradual time shift? Can that be disabled? These systems are booted a couple times a day.
When the NTP daemon is already running, it always compensates very slowly. It simply speeds up or slows down the system clock till it gets in sync with the reference, and this can take hours. It is done intentionally slowly so as not to disrupt (much) Linux processes that rely on clock timings. When the difference between the computer time and the found reference is too large, ntp simply bails out. However, when you start the ntp service, the service startup script does first a clock setup to the reference, and this can jump years if needed in a milisecond. Once the computer clock is adjusted, the daemon is started and takes over syncing the computer system clock and the reference (maybe again adjusting the clock, but slowly). You probably will need "something" to tell the operator if the system clock is in absolute sync with GPS or not, and then... well, you have to decide if your software does something or if the operator does something or whatever :-) -- Cheers / Saludos, Carlos E. R. (from 12.3 x86_64 "Dartmouth" at Telcontar)