Event Structures Are Not Working on My CompactRIO in LabVIEW

Updated Oct 27, 2023

Reported In

Hardware

  • CompactRIO Controller

Software

  • LabVIEW

Issue Details

  • I'm creating a VI on my cRIO and when I run it on highlight execution mode, I can see the event structure is not responding. Should this structure work on Real-Time based targets?
  • For this reason, we built a very basic VI (picture below). This VI works fine locally (when it run on the computer), but when we want to add these type of structures in our project with cRIO-9053, it stops working and doesn't show anything. Can help or give advice on how we can solve this issue? 

Solution

The cRIO-9053 device does not support event structures on FPGA modules, because it runs on the VxWorks operating system, which only supports dynamic events . Dynamic events are events that are generated programmatically, such as user events or notifier events. However, if the event structure in the VI is configured to handle value change events, they are static events that are generated by the front panel controls. Static events are not supported on VxWorks targets.

In general, Real-Time targets support only Event Structure with dynamic events, currently, the only exceptions are cRIO-903X and 904X which run NI Linux Real-Time and also have a display port or USB-C port (with display support).

To work with Event Structures on those, you should first enable their Embedded UI on MAX.

Another possible alternative to using event structures on the cRIO target is to use a polling loop instead. A polling loop is a loop that continuously checks the state of a control or indicator and performs an action based on the state. For example, you can use a while loop with a shift register to store the previous state of a boolean control and compare it with the current state in each iteration. If the state has changed, you can execute the code you normally would in the event case. You can also use a wait function inside the loop to reduce the CPU usage.

Additional Information

Keep the following considerations in mind when using each Real-Time Operating System that comes with NI hardware.