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<== Date ==> <== Thread ==>

Subject: Re: Making Records Invisible
From: [email protected]
To: Susanna Jacobson <[email protected]>
Cc: EPICS Tech-Talk <[email protected]>
Date: Thu, 5 Sep 2002 12:01:13 +0200
Hi Susanna,

general answer: No.

EPICS (in this case: Channel Access) does not provide any hot swap or
fall back capabilities based on redundant channels. The mere existence
of multiple channels with the same name will create exceptions (usually
seen as error messages) at the client side. Redundant channels are on
the wish list for Channel Access, somewhere in the upper half of the
middle third, I guess. (NB: Things on the CA wish list can be raised in
priority by generous donations of manpower to EPICS core development.)

Specific answer: Wrrrnnnrrrlll ... still no.

You can stop records from processing by disabling them. But this won't
touch their existence, so CA would still see them.

You can put up CA access security to have noone read nor write access to
the channels. But still CA will see the name and create exceptions.

You can set EPICS_CA_ADDR_LIST on the client side so that a client only
sees the IOC where the real hardware is. This works fine, but as long as
there are other channels on the "other" IOC that the client also wants to
see, no chance.

You could of course introduce an additional set of soft records with the
generic channel name and have two sets of hardware related records with
different names. The OUT and INP links of the generic record layer would
point to the hardware side records that are currently in use. In that
case you would get a performance hit by adding another record layer
_and_ an additional CA layer (the generic records reside on one IOC and
have to use CA to get to the hardware related records in at least one of
the two locations).

So ...

Splitting the databases to move the channels that are connected to your
hardware into a separate db file and then commenting / uncommenting the
dbLoadRecord calls in the startup command when rebooting the IOCs seems
the only reasonable way to handle this situation.

Ralph

>>>>> "Susanna" == Susanna Jacobson <[email protected]> writes:

  > Hi Folks,
  > Here at the ALS, we are making a transition from an older
  > system to a newer one over several years, one device or
  > subsystem at a time.

  > We want to be able to turn off one or more channels in the
  > older IOC, and then turn them on in the newer IOC, without
  > having to rebuild .db files for the two IOCs.  That is,
  > when a hardware connection is moved to the new sys from the
  > old, the associated EPICS records appear to move as well.
  > (Although in fact the same record is in both databases.)

  > Has anyone else done something like this with EPICS records?  
  > Is it possible?

Replies:
Re: Making Records Invisible Andreas Luedeke
References:
Making Records Invisible Susanna Jacobson

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