Hi all, I have been writing some LabView code that controls several different instruments. My general control paradigm has been as follows: Each instrument is controlled by a different VI These instrument VIs contain a connect/disconnect button. When the connect button is pressed, the instrument settings are written to the instrument, and it runs When the disconnect button is pressed, the instrument closes out and the subVI ends. The mainVI allows users to set instrument controls, which are written to global variables, and referenced inside the subVIs. (For example, the mainVI connect button is written to a global variable. Inside the subVI the global variable writes to the connect button) While the subVI runs, the instrument readings are written to global variables in the subVI. The mainVI displays the instrument readings by reading the global variables that were written in the subVI. However, since the subVI runs until disconnect is pressed, the mainVI waits for the subVI to finish, and the global variables are not updated. The mainVI user cannot update the disconnect global variable, while the subVI is running, so it runs continuously, and the mainVI user is locked out of control of the subVI. This seems like a pretty simple/fundamental use case, so I’m sure there must be a clean solution to it that I am missing. I am clearly confused about the general “dataflow” and “synchronization between main and subVIs. Can anyone suggest, or give me a topic to read up on, to allow me to use a mainVI/subVI scheme to write controls to instruments and display instrument readings?

Generally running multiple asynchronous loops requires special care as it kind of conflicts with the data flow paradigm of LabVIEW. I recommend changing your subVI into Initialize, while loop {Read} and Close VI instead. If you insist of keeping the current design, please refer to Read and Write Main VI Control/Indicator Value from a SubVI

Hi,Even though you have explained your problem nicely, it would be better if you could attach your vi (at least a simplified version).Like you mentioned it is mostly because of synchronization issue. Ther are design pattern templates (producer/ consumer) and synchronization functions (queues/notifiers) available in LabVIEW to achieve what you're trying to do. Alternatively, you can use control references to pass into your sub-vi's to access your main vi FP elements from sub vi, but i would recommend you use the first approach.Please refer it and attach a simplified version of your vi if possible.

LabVIEW

Using MainVI as front panel of controls for subVIs (running persistently)

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@ZYOng

I actually came up with this solution recently (individual VI for open, looping VI for running, individual VI for close).

Seems to be a more natural fit for the dataflow. Thanks for the help!

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LabVIEW

Using MainVI as front panel of controls for subVIs (running persistently)

Re: Use MainVI as user GUI, and subVI as instrument control