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

mass85 at tlen.pl mass85 at tlen.pl
Thu Nov 24 08:25:18 UTC 2011

> I've used gprs with usb dongle and on either Ubuntu or NetBSD.
> The main problem was the gprs being very slow to respond until
> it had adjusted to any significant level of traffic. I'm not
> sure if Ubuntu uses ntpdate at startup or if it's redundant
> with NetBSD but either way it wasn't possible to get a reliable
> timesetting at startup until I used 'burst'. It might be that
> iburst would have been sufficient by then but I had setup a pool
> server so using that option was ok for me and I had also set a
> long default poll interval.
Ntpdate works pretty fast, I can get time set in 1 or 2 seconds. The
problem is that connection setup can last long or even fail.

> At startup rtt was sometimes around
> 10 seconds and when connection was fully established the lowest
> rtt was above 150ms. I would not rely on any timings being
> useful for adjustment of hwclock.

Why not? My NTP can synchronise in 15minutes and then keep control
over system clock. I assume that when it synchronises time and adjusts
system clock, it knows what it's doing and it is doing it quite
accurately. RTC can be at least 1s off every 24h, so it is quite much.

Is there any other ready to use way than "hwclock --adjust" to
calibrate RTC? Could NTP do it?

Marcin Adamski

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