How to debug LabVIEW is a common challenge when using NI LabVIEW software. When the application doesn't run as expected, having effective debugging skills and tools becomes essential. Some techniques are widely used, while others might be unique tricks you've discovered on your own.
We reached out to JKI's LabVIEW Architects (CLA) and members of the LabVIEW community to uncover some "top secret" methods for quickly identifying, isolating, and fixing bugs. Here are some clever debugging techniques we learned:
**Using Probes**
Probes are the first and simplest tool in LabVIEW debugging, yet they are incredibly powerful. It's easy to place a probe on a wire and monitor data flow as you identify issues. Key features include:
**Save Wire Value Function**
The Save Wire Value feature in the LabVIEW development environment is often overlooked. When enabled for a VI, LabVIEW automatically saves the last value of each wire on the block diagram. Hovering over any wire, even when the VI isn't running, will display the last value via the probe tool.
**Custom Probes Without Writing Code**
With LabVIEW Custom Probes, you can create advanced debugging tools without writing any code. For example, you can create a Historical Probe that displays previous values for multiple wires, controls, or waveforms. This helps identify patterns or trends in your data without needing custom code.
**Get Custom Probes from the LabVIEW Tools Network**
Expand your debugging toolbox by using probes created by others. SAPHIR offers a range of free custom LabVIEW probes on the LabVIEW Tools Network. Download and install the VIPM Community Edition, search for ViBox, and install the probe with just a few clicks.
If you're using LabVIEW 2011, you can also find ViBox through the LabVIEW Getting Started window.
**Suspend on Call**
Many LabVIEW developers aren't aware of this feature. The "suspend on call" function allows you to pause execution and perform actions such as modifying control values before the VI runs, returning to the calling program, or skipping the VI entirely.
**Unwired Front Panel Controls and Displays**
Recommended for FIRST Robotics teams and professional developers alike, this technique involves adding front panel controls or displays that aren't connected to the connector. These controls work like debug inputs or outputs, allowing manual testing without complex setup.
**Execution Tracking**
When other methods fail, stepping through the code is an option. LabVIEW’s "highlighting execution" feature, known as the "bulb," is one way to track execution. For more detailed tracking, consider the LabVIEW Desktop Execution Trace Toolkit.
**Track Disk or Memory**
A simple way to initiate execution tracking is to log wire values in subVIs. You can write a small VI to log data to a file or use a custom probe to display historical values. This can help gather enough information to identify the root cause of an issue.
**Unit Testing**
Test-Driven Development (TDD) is a powerful method for creating better code and debugging existing code. When you find a bug, the first step is to create a unit test that reproduces it. Only then should you start fixing the problem. If the test passes, the bug is resolved.
LabVIEW has several add-ons for unit testing, including JKI’s Free VI Tester and the LabVIEW Unit Test Framework Toolkit.
**USB Debugging Assistant Based on LabVIEW**
Here’s a simple case study on building a USB debugging assistant using LabVIEW. We’ll cover how to set up communication with a STM32 USB device, which uses interrupt endpoints for data transfer.
To communicate with the device, you need to install the VISA driver generated by NI-VISA. Once installed, you can use VISA functions like VISA Open, VISA Write, and VISA Read to send and receive data.
After setting up the VISA resource correctly, you can build a basic VI to send and receive data. By using conditional structures and handling timeout errors, you can ensure reliable communication.
Finally, by implementing shift registers and managing the USB port with conditionals, you can create a functional USB debugging assistant.
**Debugging LabVIEW Programs**
In real-world applications, programmers often combine various debugging tools. By analyzing error messages, using breakpoints, and leveraging probes, you can quickly locate and fix issues.
LabVIEW provides a range of built-in tools, such as the Error List, VI Hierarchy, Breakpoints, Highlight Tool, and Probes. These tools help you understand the execution flow and identify problems efficiently.
**Tips for Effective Debugging**
- Use the Error List to identify and fix syntax errors.
- Explore the VI Hierarchy to understand the relationships between VIs.
- Set breakpoints to pause execution at key points in your code.
- Use the Highlight Tool to visualize data flow.
- Customize probes to monitor specific values during execution.
By mastering these tools and techniques, you can become more efficient at debugging LabVIEW programs and improve the quality of your applications.
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