Experimental Physics and
Industrial Control System

Kay-Uwe Kasemir <[email protected]> · Mon, 12 May 2003 08:49:47 -0600

At 14:44 5/9/2003, Seth Nemesure wrote:
>We have a situation where analog output records have a built in granularity.  If a user attempts to change the value using his/her favorite EPICS program (probe, edm, etc.), The value that actually is sent to the device may be slightly different from the value typed into the program interface due to the granularity of the underlying device.
>
>Here's the question.  What is the normal practice for display programs such as an edm screen?  Do they show the value entered regardless of the actual value that is sent or should the interface show an adjusted value based on the nearest acceptable value after granularity has been accounted?

Display programs like edm usually show the real value of the record,
that is: the adjusted value.
One reason is the one you mention: Is should display the real value,
with might be different from what you entered because of granularity
or limits.

Also: if you have an "output" widget, e.g. a slider that
the operator moves to "write" to a record, that widget might
not be the only thing that modifies the record.
The simplest case is another instance of the same screen running.
You want both screens to stay "in sync".
Operator A moves the slider on EDM screen instance A
-> screen A modifies the record
-> record sends out monitors to screen B so that screen B's slider
updates accordingly.

For this reason, all "writing" widgets are usually also "reading" widgets
so that they stay up to date.
As a side effect, "writing" widgets might switch to an "editing" mode:
A text entry field will usually display the most recent value of a channel.
As soon as you enter a key or select some part of the text,
the widget will switch into "edit" mode so that you can edit the text
without being interrupted by newly received valued of the record.
If you press return -> your value gets written.
If you leave the text widget (press TAB, click outside of the widget)
-> widget ignores what you entered and goes back into the "read" mode.

-Kay

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System