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Subject: Re: ICALEPCS and EPICS iocCore V4
From: Kay-Uwe Kasemir <[email protected]>
To: [email protected]
Date: Mon, 17 Oct 2005 14:14:19 -0400

On Oct 17, 2005, at 13:41 , Steve Lewis wrote:
1) EPICS has a narrow interface and ALAMA/ACS has a wide interface. Narrow means that EPICS just has well defined data types and wide means that ACS has object to object communication.
This is the key difference. The NIF control system also has an ALMA_like, wide, object-to-object interface. My opinion is that this nearly killed it. A wide interface is a very subtle way of replacing the benefits of encapsulation and data hiding with (larger) problem of "interface coupling".

You cannot effectively build tools; programmers need to be involved at every level, forever. Even small changes require rebuilding everything: it's "make clean; make" every night--hopefully you have a full suite of regression tests with a lab filled with real hardware. NIF has about $500K sunk in such a lab, and keeps its test team staffed at 25% of the level of the developers.

I believe that. On the other hand this talk listed by Marty:
http://almasw.hq.eso.org/almasw/pub/ACS/ACSWorkshop2005/ beyondMiddleware.pdf
.. which gives the example of replacing CORBA with ICE.
Now: hard, requires recompile etc.
Future: easy based on divine framework with interfaces to services in containers. Can replace the CORBA plugin with an ICE plugin, at run-time, going forth and back.

So who's right?

2) The interface to the IOC database is narrow in the sense that communication is done via data rather than a large set of objects. This is what allows general purpose tools like display managers and what makes it easy for other systems to talk to IOCs. In EPICS facilities it is common for operators to create displays for MEDM or EDM. I suspect that tools like the the tango gui builder would be used by programmers rather than operators or hardware oriented engineers. Thus we must be carefull about how much device orientation we introduce into IOCs. Perhaps a power supply but not a high level physics abstraction.
Again, this is what the NIF architecture is like. It is (was) extremely frustrating under this architecture to bring some functionality to bear on the hardware and to the operators. What would have taken 10 minutes with VDCT and 1 minute with MEDM in EPICS took from 1 hour to 1 day from each of 1) the FEP programmer; 2) the tier 2 programmer; 3) the IDL/SQL/RDB team; 4) the GUI programmer; 5) the tier 3 team [sequencer-like "scripts"]; 6) the CM team to "regenerate the IDL", do "make clean; make". And then you test. Elapsed calendar time: weeks to months.

We called it "IDL hell" and employed the most devious strategies to avoid items (2)-(6).
By the way, there is an intermediate approach based on SNS administrative measures.
But back to the technical aspect, did NIF just pick the wrong
interfaces and thus each change requires 2-6?
Is the other OO framework talk mostly by people who
have never actually tried it on the scale of NIF?

-Kay

Replies:
Re: ICALEPCS and EPICS iocCore V4 Steve Lewis
Re: ICALEPCS and EPICS iocCore V4 Benjamin Franksen
References:
ICALEPCS and EPICS iocCore V4 Marty Kraimer
Re: ICALEPCS and EPICS iocCore V4 Steve Lewis

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