Experimental Physics and
Industrial Control System

"Geng, Zheqiao" <[email protected]> · Wed, 8 Sep 2010 10:20:04 -0700

Hi Andrew,

   I work for Ernest and I am currently working on the EPICS applying on uTCA.
I would like to take some time to investigate the dynamic record loading for 
EPICS base 3.x, so that we can estimate the feasibility and efforts for introducing
this new feature.

   Could you please kindly offer me some materials about the current design of the 
EPICS base? Such as the requirements specification, design report and so on. I have
only in hand the IOC design manual, which is far from enough to study into the core
codes. 

   If you have any suggestions, please do not hesitate to tell me.

   Thank you very much!

Best wishes,
Qiao

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Zheqiao Geng
SLAC National Accelerator Laboratory
2575 Sand Hill Road, Mail Stop 64, Menlo Park, CA 94025-7015, USA
phone:  +1(650)926-4262                               
e-mail: [email protected]
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-----Original Message-----
From: Andrew Johnson [mailto:[email protected]] 
Sent: Tuesday, September 07, 2010 1:44 PM
To: Williams Jr., Ernest L.
Cc: Core-Talk; Geng, Zheqiao
Subject: Re: Dynamic Loading and Unloading of EPICS Device Support and Record.

Hi Ernest,

On Tuesday 07 September 2010 14:54:51 Ernest L. Williams Jr. wrote:
>
> What is the current project status of EPICS Dynamic Record loading?
> Is that only on the 3.15 trunk?

It's not even planned for implementation there at the moment, let alone 
available.  The problem is that there are *no* locks for the data structures 
that describe the currently loaded records, and any attempt to retro-fit them 
will probably cause a major performance hit on the IOC runtime.

> As we embark upon uTCA here at SLAC; we will need that functionality.

Then you're going to need to allocate a lot of *talented* manpower to help us 
implement it in version 3.x, or take a step back and re-think what you need to 
do.

One possibility might be to write code that probes the crate and works out 
what devices the IOC has to control, then generate the necessary .db file(s) 
from that information.  At that point you can fire up the IOC, load those .db 
files and start controlling stuff.  If you need to shut down just a part of an 
active IOC without affecting the rest of it, you would regenerate the .db 
files with the necessary devices removed and restart the IOC with the now 
reduced .db files, then you're free to take out the relevant hardware without 
it disturbing the IOC.  You might want to look into the DESY/KEK work on 
redundant IOCs for making the restart as fast as possible.

Alternatively start looking at Marty Kraimer's Java IOC which I believe was 
designed to allow dynamic record creation and deletion.

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harald Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System