LabVIEW
Interrupting code within an event structure
Solved!
@smallen wrote:
Hi there,
Am I right in thinking that the case structures are being selected for by the processes/subVIs 1 and 2 completing? So the case is being determined by the iteration of the loop?
Also, will this not still freeze up the VI if the "2" box is just a wait? I think your suggestion will allow me to interrupt the write and read which are over serial and practically instantaneous compared to the exection time of the process on the instrument (which is variable depending on the command and could be any value from 20 ms to several minutes)
Thank you for your help, but I think if the wait is "2" in your example, I am looking for how I can interrupt "2" itself rather than between the three processes.
The case structure is selected by the loop iteration, yes. I kept it simple for the example and just numbered them 0,1,2 but when I write code like this I will often make an enum with 3 values, naming them something short but informative (such as "Turn on", "Wait", "Shut down"), and then pass that into an Enum to Array of Enums node and iterate based off of that (this is sometimes known as a "Natt sequence"). Every time you want to have a point where you can interrupt, start a new case to split up the code more. Anything that needs to always run, i.e. a safe shut down or data saving, leave that outside of the loop.
If the VI that is box 2 is just a wait, then you just have to find a way to split up the wait. I showed one example where a "TCP read" with a timeout of 5 seconds could be replaced with a TCP read of 1 ms that ignores timeout errors and only stops the loop after getting all expected content or has looped enough time to elapse 5 seconds. You can do similar things with the "wait" function:
Since it's sounding like it's not an actual wait function, but something similar, post it and there's probably a workaround to interrupt that as well. If it's a VISA read then changing the example I made earlier to use a VISA read with a short timeout written earlier with a property node will probably work, possibly with an additional check for a termination character. Interrupts can work if it's in a separate VI as well, there are multiple options for proper signaling between VIs that you can look up or possibly make a new post about.
Hello Kyle,
Firstly thank you for your help.
I'm not sure if I explained my issue correctly. All I am looking for is for my code to recognise when a process on the instrument has finished (by calculating the time it should take and waiting until that time is elapsed) and then communicating with the instrument to receive values. The wait time is therefore just a wait - it does not need to do anything in this time, the instrument itself handles whatever the instruction is completely independently. I want to be able to interrupt at any time, for safety reasons, so I don't think making a new case to split up the code will work unless I have a sequence of hundreds of cases.
I implemented the while loop you provided and I can't interrupt it. The boolean is completely frozen out whilst the loop runs, so I cant switch its value. The full time always elapses. This is how I tried to implement it, with an example command.
Here, the command sent is "forward,x" which moves a motor forward x steps, with each step taking 20 ms. I added a small buffer time of 50 ms for safety. The case writes the command, calculates the time needed to wait... then it just waits. The boolean is useless - the program completely freezes it out. The visa name out and error then go into the code that reads back and interprets the data, which works fine. The writing of the command also works perfectly - it is just this variable, interruptable wait time that is causing a huge headache!
I hope this helps to explain my problem(s) more clearly. Thank you very much for your help.
Sam
