Experimental Physics and
Industrial Control System

Luedeke Andreas <[email protected]> · Mon, 03 Mar 2008 10:29:09 +0100

Emmanuel Mayssat wrote:

I have been struggling with a record loop.
What is the best way to implement the following.
I have a network based Analog output device type.
I want to have the option of using that device as a TTL binary output.
I want the driver to be "smart".
Let's assume I have the following records:
ao, ai, mbbo mbbi (3-state logic high/low/undefined)
If I change the mbbo to high, the ao is set to 3.7v
If I change mbbo to low, ao is set to 1.0v
The ai is readback and mbbi is computed based on the value of ai
Now, I would like the mbbo to reflect the value of the ao
If ao is set to .5, mbbo is reset to low
If ao is set to 2.5, mbbo is undefined
If ao is set to 4.7, mbbo is set to high.
The issue is that if in the latter case mmbo is set to high, ao will be
changed from 4.7 to 3.7v. If mbbo is set to low, ao is switched back to
1v.
Is the sync'ing of ao and mbbo an unreasonable request?
If not, how would you do that?
--
Emmanuel

Hi Emmanuel,

I think this is a very common problem. I had to solve similar problems
several times in the past few years.
E.g. I had two positions represented additionally as angle and
displacement, each of the four can be set.

I solved it by the use of an intermediate transform record from the
synApps package.

Transform has a bunch of fields (A, B, ...) with input links (INPA,
INPB, ...), output calculations (CLCA, CLCB, ...) and output links
(OUTA, OUTB, ...).

The feature I'm using is, that if you write field "A", then only the
other output links are written (OUTB, OUTC, ...).

If your records are writing to hardware, then you would need new records
to copy the data to the transform record.
You can as well use a bunch of calcout records directly, where you only
write if the target will change.

This prevents loops as long as you don't have only analogue values and
rounding errors in the calculations.

In your case this is probably the easier solution.
As a third choice, you could add the functionality in the device support.

If the device support is anyway specific to your hardware, then I would
suggest to add this feature to your device support.

If you want to have this feature for different device supports, I would
rather look into an EPICS DB solutions.

If someone else has an easier solution, please tell me :-)

Kind Regards
Andreas
--
Dr. Andreas Luedeke, SLS Operations Manager, Tel:+41-56-3104002
[email protected], http://people.web.psi.ch/luedeke

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System