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<== Date ==> <== Thread ==>

Subject: Monitoring Strings
From: Andy Foster <ajf@ast.cam.ac.uk>
To: Epics Questions <tech-talk@aps.anl.gov>
Date: Fri, 21 Jul 1995 12:55:08 +0100 (BST)
To Jeff Hill,

I have a problem with monitoring a string variable in
a record. 

I have a record which is capable of putting out a string
across an output link. The receiving record (which is
actually a Gemini CAR record) takes the string
in as a value (i.e it is not an input link). The CAR
record as part of it's processing simply copies the
input string to an output string.

The idea is that this output string will be used to
convey error messages and this is what I am trying to
monitor. 

If I run the record which is supplying the input string at
1 Hz, and simply change the string it is supplying between
two states i.e. "Starting" and "Ending", I can run CAU and
monitor the output from the CAR record and indeed it shows:

"Starting"
"Ending"
"Starting"
etc

Now however, if I run a fanout record at 1 Hz from which
link1 goes to a record which is supplying "Starting" and link2
goes to a second record which is supplying "Ending", I find that CAU
gives the following:

"Ending"
"Ending"
"Ending"
etc 

I don't understand why it does not pick up the "Starting" string?

I have tried to trace through the relevant EPICS code and got as far
as "db_post_events" which is called from the "monitor" routine within
the CAR record. The string has definitely been set correctly before
"db_post_events" is entered. 

I don't know where the processing goes after the statement:

/* Notify the Event Handler */
SemGive...

Could you tell me where to look after this ?
I also noticed somewhere that strings, when monitored, were treated 
differently from other "native_types". 
Has this got anything to do with the problem?

Many thanks,

Andy

==========================================================================
Andy Foster
Royal Greenwich Observatory		Tel:    44 (0)1223 374899 (direct)
Madingley Road				E-mail: ajf@ast.cam.ac.uk
Cambridge
CB3 0HA
UK


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