Experimental Physics and
Industrial Control System

Ken Evans <[email protected]> · Wed, 29 Mar 2000 11:20:54 -0600 (CST)

 > I'm Isabelle YAO and I work for the CEA-Saclay.
 > I use EPICS R3.13.0.beta11, with a SOLARIS workstation.
 > I'm in charge of the design of a vacuum synoptic using MEDM
 > 2.3.5a.
 > I would like to know if vacuum objects, like pumps, gauges,
 > valves, already exist.
 > Another question : is it possible to upgrade the library of
 > MEDM by creating new objects (like magnets, DCCT, or
 > insertion devices like Faraday cup, profilers, ...) ?

     2.3.5a is the latest released version of the original MEDM, which
was developed and continues to be developed at Argonne.  What I say
here applies to this MEDM, not the European version, with which I have
no experience.  Thomas has already responded in regard to the European
version.  Also it should be noted that MEDM 2.3.6 has been released in
beta and is nearly ready for release.  There are a lot of new
features.

    MEDM consists of a small number of objects.  It is not easy to add
new objects because the code was not designed that way, unfortunately.
There is no intention of adding new objects, especially large numbers
of them.

    So you have two choices.  (1) Make screens using the existing
objects, or (2) write other applications to do more specialized tasks.
We do both here.

     (1) Most of the vacuum control here at the APS is done with MEDM
screens using the existing objects.  Some of these screens are pretty
complicated.  It might be worth a trip here to see what has been done
and get samples, etc.  It's hard to communicate about GUI objects via
the internet, and it could save a lot of your time and give you ideas.

      Be assured that a great variety of screens can be designed with
the small number of objects.  They are more than sufficient to control
the APS, which is a reasonably large project.  We have literally
thousands of MEDM screens, as do other sites like Jefferson Lab.  Some
of these are pretty sophisticated.

     (2) MEDM cannot be all things to all people.  The first
consideration of MEDM is that it be stable and reliable.  This is not
commensurate with feature bloat.  To let MEDM do what it does well, it
is better to make separate applications for specialized and
complicated tasks.  These are called Application Programs here and
probably elsewhere.  At Argonne, we have done this through things like
Tcl/Tk scripts, IDL, and C/C++ programs.  Mostly we have used Tcl/Tk
to make small scripts that do specific tasks.  It is relatively easy
to make a nice GUI interface with Tk.  We have a library of basic
objects like the main menu bar, entry boxes, etc.  One feature of the
objects in our library is that they have help built in, so it is hard
not to program it.  That is, the user can get help on each entry box,
etc. by clicking on it.  (This is something programmers tend to not
provide well.)  For more information on the library and what we have
done you could contact Michael Borland ([email protected]).

     Nowdays, Perl or Java would be candidates for these types of
programs, but Tcl/Tk has worked well.

     The major advantage of writing Application Programs is that *you*
have control and don't have to rely on someone far away to fix things
for you.  You can do just what you want.

     People with just basic programming skills can learn and use
Tcl/Tk.  However, there are some applications that do require
performance.  These are best written in C/C++.  If they need a GUI
interface, it probably best implemented in Motif.  Programming Motif
requires more than basic programming skills and far more code to do
the same thing than in Tcl/Tk, but there are usually people around who
are competent to do this.  Also there are several programs of this
nature already written as EPICS Extensions.  One example is the Array
Display Tool (ADT).  It is designed to handle arrays of PVs, such as
BPM readings around a ring.  Or, vacuum readings around a ring.  It
was originally written after discovering that MEDM could not really do
that for several hundred BPMs to say nothing of having all the
features that ADT has.  It and the other EPICS Extensions are
available through the regular EPICS distribution channels.

     At the APS the tendency has been to write C/C++ programs only
when absolutely necessary.  The bulk of the Application Programs are
Tcl/Tk, and this has worked out well.

     I should say that part of the need for advanced programs has been
supplied by the SDDS toolkit, also available as an EPICS Extension.
This is a topic in itself, and you should refer to the EPICS
Documentation or contact Mike Borland for more information.  These
tools are more used for analysis than control.

     Finally, in light of what Thomas said, I will say that MEDM 2.3.6
has the ability to replace all or parts of the screen based on the
values of a CALC expression involving up to five PVs.  These parts can
be read from other ADL files.  This is a new feature of the MEDM
Composite object and seems to be similar to what Thomas described.
There are also animated GIFs where the frame displayed depends on a
similar type CALC expression.  You could use these to display the
state of a vacuum valve pictorially.  There is even a new Epics
Extension called Simple GIF Animator (SGA) to help make the animated
GIFs.  My advice, however, is to follow the KISS principle and keep it
simple (and hence manageable and reliable).

	     -Ken

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System