[vdr] Re: Time jumps

[Sergei Haller <Sergei.Haller@math.uni-giessen.de>]

On Tue, 24 Dec 2002, Harald Milz (HM) wrote:

HM> Sergei Haller <Sergei.Haller@math.uni-giessen.de> wrote:
HM>
HM> > But  I  think,  we  had  many complaints about clock jumps in the past, so
HM> > probably this should go into the final 1.2.0.
HM>
HM> I think the best way is to run ntpdate once and then start xntpd _before_
HM> vdr starts, provided you have an NTP server within network reach [...]

If  one  has  an NTP server within network reach, then xntpd (or other ntp
client) is by far the most preferred way to update the clock.

if  not, updating the time from the dvb stream is better than nothing. The
problem  is,  that (AFAIK) the time stamp is not very accurate even within
one  transponder.  but  if  you  switch to another one, you may even get a
wrong time stamp (off by several secs/mins or even hours)

does someone have more information on the transmitted time stamp?
 - which format does the time stamp have? does it include microseconds (I
   doubt it makes sense to transmit them because of the different lengths
   between the sat and the dish depending on the geographic location, but
   who knows?
 - how accurate is the time stamp within one transponder?
   does it jump back and forward?

one possibility would be to do the following:
   if the system clock is off by at least XX seconds (what is a good
   value? 2? 10? 20?), then set the clock, causing a time jump on the
   system clock.
   if the diff is less than XX seconds, use adjtime.

with that, if one uses always the same transponder for time synching and
the transmitted time is not jumping, after some while the system time
should get more and more correct (like with ntp)

c ya
        Sergei
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