Weird behavior of feedback node in sub-vi

[YePererva]

Hello!

I try to implement the low-pass filter sensor reading and it worked well while it was part of main VI. As soon as this part was moved as Sub-VI, the behavor became messy. From what I see, it looks like it has always 0 as previously calculated value instead of remembering.

Is there any hint, where to dig to fix it?

 

[GerdW]

Hi Ye,

maybe because you initialize the feedback node every time?

(Your main VI uses way too many local variables IMHO -  and too many IndexArray nodes…)

Suggestion:

[YePererva]

What do you mean "initialize every time"? It is set to be initialized at first call.

I don't see how your suggestion is different from mine. Or you want to say to return the feedback node to the main vi?

[GerdW]

Hi Ye,

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@YePererva wrote:

What do you mean "initialize every time"? It is set to be initialized at first call.

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But there are several calls of that VI…

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@YePererva wrote:

I don't see how your suggestion is different from mine. Or you want to say to return the feedback node to the main vi?

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My version doesn't need the formula node.

And I would use feedback nodes in the main VI to get rid of all those local variables…

[Yamaeda · Accepted solution]

The subvi is tricky. Sinve you have a feedback node and calls the VI in 3 places, you'll get the wrong feedbacked value for the next call. It should fix itself if you change it to Reentrant Preallocated mode.

[YePererva]

Needed to edit sub-VI properties:

1. Open Sub-VI

2. Go to its properties (Ctrl+I)

3. Switch to category "Execution"

4. Select  "Preallocated clone reentrant execution"

5. Save

After that it worked properly.

Regarding the local variables: those are additionally used in other places of VI. 

[YePererva]

I must be missing something. Where is this "Reentrant Preallocated" setting?

[GerdW]

Hi Ye,

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@YePererva wrote:

Regarding the local variables: those are additionally used in other places of VI. 

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Then you should reconsider your overall program design…

[thols]

It's a kind tip from us that will improve your programming skills to not use (local) variables. Much easier to read the code and less bug-prone. Think dataflow! 

[YePererva]

Probably, that will be done after introducing all the functionality I need. As of now, this is still a "functional prototype under construction".

P.S. Please, explain how does use of local variables compromise the data flow?

As I understood, the main part responsible for dataflow in such application is the state machine and connection between states. In NI course(s) there is a strong suggestion "one state - one function". So, in this case I have several states: "Data acquisition" (reading of 7 sensors, but there will be a few more latter ), "Statistics" and "Data filtration/noise suppression", where extra calculations are made. Usage of local variable seems to be the proper way of passing data between those stages. What is wrong with that?