What are user defined variables (UDV)?

[craige]

I am trying to debug a real-time application and have been working down the known issues for LabVIEW Real-time 2011. There is a termed called "User Defined Variables (UDV)" that pops up occationally in the known issues document along with some other documents. It appears that UDVs can be created under FPGA targets but I'm unable to find any useful information on them. I'm only familiar with local, global, shared, single process, and IO variables.

[Shalins]

see if this helps you...

http://digital.ni.com/public.nsf/allkb/F3F36FD87DA9D94E862578F600697892

[craige]

Thanks for the link but you kind of just proved my point. I've only been able to find a reference to UDVs in the article you referenced in addition to a few CARs. Wasn't able to find anything about what they are, how they are created, etc. Maybe this is an NI internal thing that R&D just forgot to share with those outside of NI.

[tannerite · Accepted solution]

Hi craige,

The Using I/O Variables help documentation give a pretty good explanation of what a user-defined variable is under the section "I/O Variables for Custom FPGA I/O Data". I hope this documentation helps!

Best,

tannerite

[craige]

Tannerite,

The term User Defined Variable and User Defined I/O Variable seem to both refer to the same thing. I guess the clarification is that an I/O Variable could include things like System Temperature and other variables supplied by default when adding an FPGA target while User Defined Variables are those used to access the FPGA I/O via the scan engine. Hopefully this assumption is correct. As a developer syntax is everything so small discrepancies in naming conventions make a big difference in comprehension and use. This was a bit confusing. Thank you for the clarification.

Craig

[tannerite]

Craig,

The above is mostly correct. An I/O Variable is the shared variables that the Scan Engine creates for modules. A User Defined Variable (UDV) allows you to create variable that can be accessed from the I/O Variable Engine, similarly to a standard I/O Variable. The UDV allows you to customize what it is connected to while an I/O Variable points to a specific I/O on the module. I am glad you are more clear on what it actual is though!

Best,

tannerite

[craige]

I have not attempted to place these items in my main 9074 chassis for two reasons

1) My 9074 module host modules critical to E-Stop monitoring

2) This would required recompiling my FPGA code which is a time consuming process.

Still a good suggestion that I will have to assess with the test system manager.

The application does not stop running but simply posts these errors then eventually starts reading correctly again. These error often times occur for about 5 minutes then magically disappear and the system operates as expected. I am only seeing these issues intermittently. Sometimes the system will run for 12 hours just fine and all of a sudden the errors occur. I'm keeping an eye on memory since perhaps I have a leak that is causing this problem to occur (although i'm not sure how the errors get resolved if this were the scenario).

Nothing else noticeable is occuring when the error occurs. The rest of the system (including other IO found on the same module and chassis) are read just fine. I've attached some screenshots of these two loops.