Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Wed, 09 Dec 2009 10:58:26 +0100

Hi Andrew,

My personal opinion is that a record which is not processed should not "do"

anything. That means it should not cause other records to process and should not

change their value. I think the original idea behind processing a record is that

this is the only time where a record is "active". Maybe apart from the time when

it initializes. But even then it should not process other records.

Let's assume this situation:
ioc1:
A
B.OUT-> C

ioc2:
C
D.INP -> A

I think the "correct" behavior is:

When ioc2 reboots, C becomes INVALID/UDF and only gets a copy of B when B

processes. D gets initialized with a copy of A. Neither C nor D gets processed

unless they have PINI set.

Dirk

Andrew Johnson wrote:

Hi Geoff,

On Monday 23 November 2009 16:52:43 Geoff Savage wrote:

Here are the details of my testing with a summary preceding.

Thanks for that very helpful and detailed bug report. For others, I'll quote

Geoff's original message to explain what's happening:

On Friday 13 November 2009 13:38:36 Geoff Savage wrote:

I have a passive stringout record in IOC A whose OUTLINK references an
mbbo record in IOC B.  When I reboot IOC B the value in the stringout
record is written to the mbbo record even though the stringout record
has not been processed.

I have confirmed that exactly the same thing occurs with the latest release,

and after studying the history of the code it looks like this behavior may

date all the way back to 1996.

The good news is that it only happens when the data type used is a string, so

if you replace your stringout with a longout or another mbbo it will stop

happening. That changes the coupling between your two IOCs slightly since

you've moved the string to state conversion, but it doesn't really increase it

because the strings had to match before anyway.

The bad news is that it looks like Marty intended this to happen for all data

types, as he went to the trouble of storing a copy of the data and recording

the fact that the link had actually been used. In practice non-string output

links don't re-send their last value on reconnection because the link flag bit

pvlOptOutNative never actually gets set anywhere in the code.

The question at this point is whether to change the current behavior for

string data. Given that EPICS users are not used to this my inclination is to

stop it happening for strings too, but I'm open to argument on that. In the

future we might add a link flag to allow the DB designer to control whether

this should occur, so I will probably leave the implementation in place anyway

and just disable it for now.

Any comments?

- Andrew

--
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System