[ntp:questions] NTP on embedded Linux with GPRS connection

mass85 at tlen.pl mass85 at tlen.pl
Thu Nov 24 17:44:17 UTC 2011


> There is an inherent difficulty in hwclock. When you determine its drift
> rate, the computer is on and warm. When it is acually useful, to tell
> the difference between the rtc time and true time, the drift rate is
> different because the computer is off (cold). This has a few PPM (up to
> 10) effect on the drift rate.

My device is not a computer, its temperature is lower. But on the
other hand it is sensitive to the outside air temperature that can
vary during a day or a week pretty much. In this case I'm not sure if
any calibration makes sense.
>
> hwclock, at least one version of it . There are ( were?) two development
> streams with the same name, but different behaviour. One  does try to do an rtc recalibration
> as well. Again it has nothing to do with ntp. It sets the clock before
> ntpd gets it.
>
Are you talking about Busybox and regular implementations of hwclock?
The former one does not apply any corrections to RTC. The latter
calculates RTC's drift when we write to RTC. Can ntp call
automatically some script whenever it gets close to reference clock?

Marcin



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