Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 02 Jul 2004 13:47:49 -0500

Luedeke Andreas wrote:

at the SLS we upload the channels at boot time from the IOC to an oracle
table. This is done by a perl script running on the boot pc started by
the ioc using rsh, reading a file generated before by the IOC using the
dbl command. Not quite the portability you would like to have for epics
3.14 applications: you need to save a file from the IOC and you need to
have an rsh mechanism.

The rsh mechanism is not essential if you arrange to have a program
running on the fileserver which is monitoring all of the dbl output files;
when it notices a change it triggers the update sequence. If you're not
so worried about short delays you could also just have a cron job that
periodically checks for updates. This might also be more appropriate if
the processing after a reboot can take a long time to run, as you can
limit how often the processing can be started.
Bear in mind that the list of PVs (i.e. CA Channel names) is not the same
as the output from dbl, which just gives you the record names. A truly
omniscient nameserver would also need to know the record type, and the set
of publicly accessible field names for that record type on that particular
IOC [don't forget that two IOCs that use two different DBD files can have
a different set of fields in the same record type, you must make sure
you're using the IOC's DBD file to be sure what fields it will have]. A
simple way to resolve this would be to dump the DBD file at boot time as
well as the dbl output.
It should be relatively straightforward to write some IOC-side code which
queries the database in memory using dbStaticLib routines, and sends the
results directly to the name server; I'm not aware of anyone who has
actually implemented something like this though. This code would be able
to resolve the field names issue without having to write a parser to
extract the DBD filename(s) from the st.cmd file.
- Andrew
--
Dear God, I didn't think orange went with purple until I saw
the sunset you made last night.  That was really cool. - Caro

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System