[ntp:questions] Re: disciplining two clocks with the same ntpd?

David Wuertele dave-gnus at bfnet.com
Fri Jan 23 18:16:40 UTC 2004

Piotr> You should discipline your system (software) clock with NTP,
Piotr> then store the time into RTC once every few minutes (default 11
Piotr> under Linux with PPSkit).

I know that's what I *should* do.  But here's my problem:

1)  The RTC clock is more accurate than the system clock
2)  This is an embedded system where there may or may not be access to
    the Internet
3)  I need to configure all systems the same whether they have full,
    spurios, or no access to the Internet

So I figure I could slave the system clock to the RTC as the default,
and then if the access is available, that will discipline the RTC.

If I were to try, as you suggest, to discipline the system clock by
the in-accessible Internet, then write the system clock to the RTC,
then I would have the not-very-accurate system clock disciplining the
more-accurate RTC, which I want to avoid!

Piotr> Please note, that any get/set time on RTC clock (x86):
Piotr> a) wont give you more than 1-seond accuracy,

...which doesn't seem to be a problem for me.  I only need my clocks
to be acurate to +-1 second or so.

Piotr> b) will have too huge jitter to make it useful.

...I don't understand, how does the jitter make it useless?


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