Experimental Physics and
Industrial Control System

Hi Folks,

A colleague puzzled me with a db that shows surprising behavior.

An aSub record is triggered periodically though a CP input link. It
looks up if it needs re-initialization (the user can press a button to
request that). If yes it does an additional calculation. After
processing it resets the record that requested the re-initialization.

See the attached .db file.

Usually when the user presses the button to re-initialize, the aSub does
the additional calculation once and then goes back to normal processing.

But the calculation may may take a bit too long -- longer than the rate
of the CP input link monitors. In that case, the record never leaves
initialization mode!

I have simulated the slow calculation with the attached subroutine code
which simply waits. (I know that is is a bad idea to wait in a
synchronous subroutine. The original code does not wait but calculates.)

I think that this is an effect of lock sets because the "mode" record is
as well input being processed by a caput as well as output of the aSub
record. But is this the intended behavior?

The CP monitor finds the record busy (PACT=1) and arranges for
re-processing when the record is done. But should not the FLNK be
processed and the mode record go to 1 before the aSub runs again?

Any idea how to fix this? Is it necessary to make the subroutine
asynchonous? Making the links from and to "mode" CA links does not fix
it. Scanning the aSub itself with ".1 second" does not show the strange
behavior, it simply delays the scan thread.

Puzzle for the weekend...
Dirk