Experimental Physics and
Industrial Control System

Timothy Madden <[email protected]> · Tue, 05 Aug 2008 10:01:22 -0500

James
Thanks for the email. Sounds like you have gone down this road before,
and just making Python a client may be the easiest way. I will dig into
the Python CA client stuff. Do you have to have a continuously running
Python loop to monitor the PV's. Do you really need an SNL program at
all of you have Python monitor PV's and do all the work? Seems like you
can just have an IOC with some standard PV's that don't do anything but
store values, and have Python do everything interesting.

Tim

Rowland, J (James) wrote:

Hi Tim

At Diamond we use Python for beamline simulations, some using serial ptys or socket servers to interface to the standard asyn drivers and some recent ones implementing asyn ports in Python itself. We also use some Python device support for waveform calculations, and we have even written a Python interface to the portable channel access server (not so useful). It's a good approach for simulations but considering how much interface code we ended up writing I would recommend the SNL way of doing things if you can get away with less tight integration with the database. Your Python script would use the CA client libraries to monitor PVs on the IOC and write back results. We use that method to good effect with Matlab. You can easily add a new command to the IOC to start the Python interpreter in-process like SNL does. I can send you some examples if they would be useful. I think KEK also had some Python device support.

James

________________________________
From: [email protected] on behalf of Timothy Madden
Sent: Mon 04/08/2008 15:56
To: [email protected]
Subject: EPICS to Python / EPICS to Tcl

Folks
I want to make an IOC that does the following:
Serve PV's that call Asyn, They could BI, BO or any standard record.
Make an Asyn driver that is linked with  a Python or Tcl interpreter.
The IOC written in C, would then call scripts which could be stored as
text files on the disk.
A record named "X" would call a script function named "X" and pass its
PV value to it. Likewise, the output of the script could be passed back
to the PV value. Python and Tcl interpreters provide ways for C to call
scripts, pass and retrieve data from scripts. Also, it is not too hard
to link  an interpreter into a C program. All that is needed is to write
the ASYN-based C functions that call the interpreter. It could be done
in Linux or Cygwin.
In this way, one could make an IOC to do whatever one wanted without
ever messing a C compiler. The user would write a few scripts, make a
st.cmd file, and a db file. In this way, new IOCs could be very quickly
developed.
Has anyone already done this?
Tim Madden

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System