LabVIEW
Producer consumer continous data retrieval
Ok, so firstly, good job with commenting up some of your code, and attaching the whole project rather than broken bits and pieces.
With regards to your problem, you have the dequeue element outside all of your cases. This means that will dequeue one element of the queue per iteration of the outer loop.
When you press Standard Test, you enter a new loop, which waits for M1's local variable read to be between 59.9 and 60.1. This condition will never be satisfied since a) M1 is generated between 0 and 10, and b) only one value of M1 (the current value) is considered - the dequeue won't be used again until the end of the inner loop's event, which never happens, because the loop in the middle never stops.
You need to dequeue inside the inner loop if you want new values, and you need the condition to at some point be true to ever get out of the inner loop.
You also have a compound arithmetic OR on a single value. This does nothing! 🙂
What I meant was more that the Event Structure's case for Standard Test: Value Change starts a loop which checks the same value read from the M1 and M2 local variables to be between some limits.
The values which are checked never change - they are read before the loop starts (you see they are wired into the left side of the while loop in the image).
If they don't satisfy the check on the first iteration, the loop will never end, because the values never change. It looks like what you want is to repeatedly check the values generated in a producer loop, and wait for them to satisfy some condition in the consumer loop.
Hopefully you can see that the main problems is due to your flow of data - although you move the dequeue element inside the test selection case, this is probably worse! What you really want to be doing is removing the inner loop because this is blocking the outer loop from iterating. In a text language, this would be something like (terrible pseudo-code follows!):
while ! stopCondition do {
get MValues
if StandardTest clicked, do {
while M1 not between valueA and valueB {
continueForever
// See the problem here?
}
}
}
Hopefully my dubious text-based pseudo-code, complete with whole sets of mixed-language syntax, has highlighted the problem. You dequeue is outside of the loop that checks, and then you forever check the same values against some condition. This either passes on the first attempt, or locks forever!
Bob's rather excellent post has you covered with a lot of good points, but to try and give you a hint as to where to start, you should look to the middle of what he wrote. (Note - you should read all of his post, and carefully - it has a lot of key points for architectural design that will help you a lot in the future!)
@Bob_Schor wrote:
As I understand it, what you want to do is to look at incoming data (in your Consumer). In your initial state, you are looking for certain conditions to be met (the data must be between X and Y, or you need to see "three in a row", or the User needs to Push a Button). When the condition is satisfied, you move to a new State where you Save the Data, Plot the Data, Do Something Else with the Data, and you stay in this State until something else occurs, at which point you move to yet another state.
Well, LabVIEW has you covered here, as well. Open LabVIEW, click Create Projects, look under the Desktop Templates for Simple State Machine, and study the example.
The key point here (as I see it) is that your data consumer shouldn't be locking itself out of getting new data! As you can see from his detailed explanation, the idea of a state machine here is that rather than having a case which starts a loop checking the inputs for some condition (between 59.9 and 60.1, for example) you can have a case which says - is this condition satisfied? If yes, go to the next state. If no - go to the same state. Here, you can have it so that each iteration of your consumer, if the condition is not satisfied, you remain in the same "Check condition" state, and never start what is step 2 (case 1) of your Stacked Sequence Structure. Once your condition is satisfied, you can wire 'Step 2' to your state output from that case. See the example State Machine for more details!
Edit: The state machine example is called "State Machine Fundamentals", at least in LV2016, and as far as I can see there's no template under "New...", just the example. Contrast this with the Producer/Consumer, which you've already found the template for.
