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

Subject: BI-Directional PVs
From: "David H. Thompson" <thompsondh@ornl.gov>
To: techtalk <tech-talk@aps.anl.gov>
Date: Fri, 14 Feb 2003 16:40:01 -0500
My application is device support into a shared memory area that other,
non-epics, processes interact with.  The application needed for some of the
PVs in shared memory to be adjusted either from a remote location via
channel access or locally from the shared memory client application.  The
user wanted to be able to monitor the data in shared memory and also be able
to set the value there via the same PV.  I am using IOC core, (3.14.1 on a
windows platform) instead of a CA Server.

Looking at record support for ai,ao, long in and out, and binary in and out,
as well as waveform, it seems that "input" records provide the best way to
support bi-directionality in IOC core since record support there does little
to the record before calling the input routine in device support.

I also noticed in the record reference manual that the PUTF field is a
logical that happens to be set if dbpf, or channel access, is writing a
value to the record and if SCAN is passive.  This lets the device support
know that data should be written instead of read.  Scanning can be
accomplished by using an flink from something that is scanning, say a
fanoutRecord.

Question: Who else has done this and if so is there a better way to do it.
What am I missing?


Replies:
Re: BI-Directional PVs Marty Kraimer

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