RE: [chrony-dev] makestep command sometimes makes chrony stop reading its sources

["Hattink, Tjalling (FINT)" <T.Hattink@xxxxxxxx>]

>From: Bill Unruh
>Sent: Wednesday, January 20, 2010 17:42
>
>On Wed, 20 Jan 2010, Hattink, Tjalling (FINT) wrote:
>
>>
>>
>> I've looked into the initstepslew command but I think it only works 
>> for NTP sources, and I only have a reference clock available (SHM, 
>> PPS). Also
>> the
>> reference clock is not immediately available after chronyd is
started.
>
>Why not. The clock should deliver nmea time sentences almost
immediately.
>Just make sure that the gps clock is switched on before the machine is.
>(Use an external gps like the Garmin 18).

The system I'm using for running chrony is an embedded box where both
the
cpu board (running linux+chrony) and the gps card are embedded together.
So when the box is turned on both gps and cpu board are powered on at
the
same time. So it takes some time before the GPS has a properly synced
clock and GPS lock. Also the box can be turned on while there is no GPS
antenna connected at all and the clock on the GPS card is freerunning
and of no use for chrony.

>> It
>> takes a minute before the SHM interface starts providing time
samples, 
>> as GPS needs to lock in. It can even take much longer, for example 
>> when the GPS antenna is not connected during start-up, but is
attached 
>> an hour later. So even if initstepslew is able to handle reference 
>> clocks I'm not sure if it will work when the reference clock is not 
>> immediately available.
>
>So, you want to ask what to do if a) the RTC is way out, b) and all of
>your external sources are non-existant. There is of course nothing that
>can be done. Now an external source turns on. You can now restart
chrony
>after those sources turn on. One of the features of chrony is that it
>allows you to enter the time by hand. Ie, if your server comes up in
that
>situation, you can use chronyc to have you look at your calendar and
your
>wristwatch and set the time.
>
>(Of course in that case, just using "date" would work as well.)
>
>What would you imagine that chrony could do in such a situation?
>

There box needs to work fully automatic, so I cannot expect users to
manually restart chrony or issue commands to step the time. I do not
expect
chrony to sync the time when no reference clocks are available, but as
soon
as an external source becomes available I need chrony to get the system
clock and rtc disciplined as soon as possible, even when the initial
system
time or rtc is way off. For example, the box could have been on the
shell
and turned of for a year, so the rtc has probably drifted considerable.
Maybe the rtc battery was even depleted so the rtc time would be reset
to
1970. Such a huge offset can only be corrected by a makestep command.

Keep in mind that chrony is used in a different context on my box than
what
you're used to see. Chrony is solely running on an internal reference
clock
instead of using external ntp servers. This type of setup is brand new
for
chrony but it already works very well under normal conditions. 

--
Tjalling Hattink

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