Experimental Physics and Industrial Control System
Dear Andrew, dear all,
I want to remind you that we are highly interested in base modifications
for IOC redundancy. For sites which are not interested in redundant ioc
operations there would be no additional code overhead if the additional
code is in "#ifdef"'s. Nine files of the epics base are effected by
these changes (mainly small ones).
The proposed model gives maximal freedom of usage.
-- If the define (REDUNDANCY) is not done, Episc runs as usual and no
additional object code is loaded.
-- If REDUNDANCY is defined (base extensions included) but not any
additional redundancy software (RMT) loaded, Epics is running as usual.
If you want to use some of the new features on some but not all your
ioc's, then this is important.
-- If you add the redundancy software RMT (= redundancy monitor task),
even on non-redundant ioc's, you are able to get information from all
tasks which have registered to the RMT registry. If you use the
sequencer extended to support RMT, you can debug your SNL programs. A
CSS-plugin is available for this. Debugging allows you to:
- view programs, state sets, variables in a tree
- view and change (force) unconnected and connected variables
- view and change current state
- start, stop and single-step each state-set
- use CSS object contribution with variables
-- If you have a second IOC as a redundant hardware, the RMT on the ioc
will manage the redundancy state of the ioc. It will control updating
the non-selected one and starts or stops activities during switch-over.
During normal operation records and state programs are synchronized
between the ioc's so that a switch-over is relativly smooth.
Some more details have been described on the last Epics Meetings.
We think that our changes are ready(*) so far. We have continuously
tested the redundant ioc pair for 40 days on a Intel-based PCI
plattform. In November we had already a discussion with Andrew and
others. We have fixed some weak points meanwhile.
We are convinced that we now have reached the state in which redundancy
should become part of the next Epics release. Any feedback is welcome.
Bernd
(*) The definition of the hook pointer still has to be placed into the
proper file of the Epics base (task for Andrew).
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