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Subject: RE: EPICS internals talks?
From: <[email protected]>
To: <[email protected]>, <[email protected]>
Date: Fri, 21 Jan 2011 22:44:02 +0000
Hi All,

OK, last week I gave my EPICS Internals talk. It isn't too polished, but I will put it up here for comment. The result is available on the following links:

http://controls.diamond.ac.uk/downloads/other/files/EpicsInternals.ppt
http://controls.diamond.ac.uk/downloads/other/files/EpicsInternals.pdf

I feel that it can be used as a start for other similar talks. I spent quite a bit of time on the UML sequence diagrams at the end of the talk and I feel, if they are accurate, that they are also useful for other documentation. I know the ca connection is a bit abbreviated, but I think the others are OK.

In doing this, the main things I was surprised to find was that:

1. The reply from a ca_put_callback goes from the task that calls recGblFwdLink, to cbLow, to CAS-event. The cbLow was a surprise, which allows the event queue to get even more out of order.
2. All ca_monitor responses seem to call dbLock/dbUnlock in the event task. Surely this is only needed for arrays? I feel that this is a lot of unnecessary lock/unlocks.

Anyway, comments welcome.

Cheers

Nick Rees
Principal Software Engineer           Phone: +44 (0)1235-778430
Diamond Light Source                  Fax:   +44 (0)1235-446713



-----Original Message-----
From: Andrew Johnson [mailto:[email protected]]
Sent: Tue 04/01/2011 17:45
To: [email protected]
Cc: Rees, Nick (DLSLtd,RAL,DIA)
Subject: Re: EPICS internals talks?
 
Hi Nick,

On Wednesday 29 December 2010 08:11:12 [email protected] wrote:
>
> I think this is already too much for the time allotted, but I would be
> willing to hear people's comments/suggestions on the way this is going.

Many interesting ideas, although as you say there's a lot more material there 
than you have time for.  I'm not sure if you know about the detailed record 
processing walk-through of a simple 3-record chain in the second half of my 
Database Principles talk, see http://www.aps.anl.gov/epics/docs/USPAS2010.php 
slides 40-50.

- Andrew
-- 
If a man is offered a fact which goes against his instincts, he will
scrutinize it closely, and unless the evidence is overwhelming, he will
refuse to believe it.  If, on the other hand, he is offered something
which affords a reason for acting in accordance to his instincts, he
will accept it even on the slightest evidence.  -- Bertrand Russell



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Re: EPICS internals talks? Andrew Johnson

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