When to use Parameters vs File Global variables?

[testdesign]

What is the rule of thumb on when to use "Parameter" variables vs. using "File Global" variables?  TestStand documentation explains to use Parameters to pass data to a called subsequence from a sequence or vice versa.  However, File Globals are accessible by all sequences.  It seems easier to just use a File Globals but I also see documentation that says use File Globals only when really needed.  Thanks!

[santo_13]

If you use FileGlobals, it limits your sub-Sequence to be closely tied to the variable names and the variables being a FileGlobal in the new sequence where you reuse it.

If you had used Parameters, the sub-sequence can take in any type of variable and not be closely coupled to any sequence file.

This is analogous to whether you use controls on the connector pane for a VI or directly use Global variables inside the VI.

[stefanha]

General rule of thumb in programming is to use the lowest access scope possible for variables. There are many reasons for that, e.g. transparency, data safety, debug-ability. For TestStand this means to use Locals whenever possible. Use Parameters only when Locals are unsufficient. Use FileGlobals only when Locals and Parameters are unsufficient. Use StationGlobals only when Locals, Parameters and FileGlobals are unsufficient. As always in life there are exceptions, but you'll never wrong badly following that. Stefan

[3d0g]

It sounds like you might know the answer I seek.  Which one is used to stuff the $(UUT) macro when specifying the report filename path by expression?  None have worked for me.  Perhaps you know what I don't.

[stefanha]

I am not sure this is related to the original question, but whatever you set to the Parameters.UUT.SerialNumber variable in the PreUUT callback sequence will be used to replace the $(UUT) macro.

[3d0g]

I see it as related, and I thank you for a response.

I'm trying to set it from mainsequence.  I don't think it's possible.  This is the sequential model by the way.

[stefanha]

I am by no means profound on that topic as we do not use the NI process models but I believe that it should not be possible from the MainSequence.
When you set a breakpoint in the Model before the MainSequence is called, you will see that the report file is already created at that time (only the content will be added later). Which makes sense when thinking about On-The-Fly reporting.

So it is hard to imagine you'd be able to interfere with the file name after it is already created.

Stefan

[3d0g]

Hence, the serial number absolutely must be known before the start of the test of the UUT.

Thank you.

[stefanha]

You can move all steps until and including the one that gets the UUTs serial number from the MainSequence callback into the PreUUT callback sequence.
Other than that, I don't think there are reasonable options.

[stefanha]

Or you can obviously modify the template SequentialModel to work the way you need it to.

Stefan