Subvi does not stop from the mainVi immediately when the stop button pressed in the mainVi

Question

Hi guys,
I have a mainVi which has a subVi inside. I want to have a kind of emeregency stop button in my mainVi.
when I pressed the button, the program does not stop instantly. it does one loop and then stops.
please help me to solve this problem.
Attached you can find the Main and SubVI
Attachments:
Sample2 MainVI.vi ‏18 KB
Move_MINI Editted SubVI.vi ‏13 KB

Answer 1

This is basic dataflow. Any code is available to run as soon as data is present on all its inputs. No data is present at its outputs until all the code inside has completed.
What this means in your case is that the stop button will likely be read almost instantly when the while loop starts an iteration. It will not be read again until the start of the next iteration. This is why it will usually take an extra iteration to stop. You can either force it to read the stop button after the other code inside the loop completes or use a Producer/Consumer (events) architecture where the stop button will be read in a parallel loop containing an event structure.
It also means that the Move_MINI subVI has no means of responding to any external events (such as the stop button being pressed) after it has started running. All the other subVIs are missing so it is hard to tell what is going on. From the control labels and VI names I suspect that this may be some kind of motion control system. If so it probably takes 100s of milliseconds to seconds or longer to complete a move. To allow an external event to modify the behavior of such a VI, you need a means of communication between the event (stop button) and the VI. A notifier may be an appropriate choice. The VI also needs to be configured in such a manner that it never goes more than about 100 ms without an opportunity to stop. Without knowing more about the subVIs, I cannot say how this might work.
Lynn