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Subject: generalTime & EventTime
From: "Kalantari Babak" <[email protected]>
To: "Andrew Johnson" <[email protected]>
Cc: "Korhonen Timo" <[email protected]>, <[email protected]>
Date: Wed, 2 May 2007 16:54:05 +0200
Hi Andrew,

I have summarized our discussion in the last EPICS meeting at DESY
regarding the generalTime/EventTime driver issues as the following:

1. Central part of generalTime which manages the time providers will be
moved to EPICS base. The time providers (VW, NTP, Event, etc.) are
plugged in as drivers. The iocClockRegister.c will be integrated in this
central part and has to support all platforms (OS).

2. EventTime driver will completely rely on generalTime as an external
time reference (e.g. at init or when the master clock wants to lock to a
reference time). It never contacts NTP server directly. To do so we have
to change the generalTime such that a time provider which is correct can
read generalTime clock by implicitly excluding itself from the list of
time providers.

3. The generalTime API has to be changed in order to separate GetEvent()
and GetCurrent() registration because epicsTimeGetEvent() only makes
sense for the event system.

4. In EventTime we should provide the users with possibility to specify
automatic/manual clock validation after clock failures. The manual clock
validation will be implemented by an "aoRecord" soft device support in
which VAL field determines the tolerance of the difference between
EventTime time and the reference time (which is given by generalTime,
see point 2.) at the time of validating.     

5. An API (e.g. a config command) will be provided to specify which
event card (e.g. EVR/EVG) in a system is to be used by EventTime driver.
This should be called at the startup (by users). In principle we could
implement the same method for NTP Time provider to specify which NTP
server has to be used.

6. The OS time (e.g. vxWorks) should be the last time provider which
always has to give a value for the time when all the other time
providers are faulty. 

7. This is more a question: the point from Stephanie Allison is still
not clear to me; my understanding was that she is only interested in
event time only when she has given a positive event number to TSE field
and otherwise (TSE=0) she is not interested in the time which is
provided by event system. But this means to use two different time
provider at the same time (priority problem?). 

8. Finally we may change the name "generalTime" to something different;
maybe iocTime or iocTimeManager whatsoever. 

Please let me know your comments if something needs to be changed or
something is missing. 
Sorry that the e-mail is a bit too long.

Regards,
Babak


Replies:
Re: generalTime & EventTime Kay-Uwe Kasemir

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