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Debugging Explained for Arduino

What is Debugging?

Everybody who writes software with more than a few lines, knows that it won't initially work as expected.
Debugging is the task of finding bugs in your software.

A debugger is a tool that helps a programmer in finding bugs.

Debugging Without a Debugger

Without a debugger, you probably write test code that sends text to your PC:

To stop a running sketch at a certain location, you probably use this:

or this:

or this:

Writing such test code has the following drawbacks:

• It is time consuming.
• It uses precious program and data memory on your board.
• There is a high risk that you forget some places where you put test code and it will still be there in your final program version.
• Stopping a sketch might be easy, but try to continue it with the above methods!

Debugging support with the Visual Micro Debugger

With most boards, the Visual Micro debugger uses Hardware Serial or Software Serial to operate. For newer 32 bit boards, such as the Arduino Zero, a GDB based option is also available (but only recommended for experts and in some cases is a less useful, more difficult solution). Learn more about Extended GDB debugging.

The key element of all debugging is breakpoints.

With the Visual Micro debugger, you simply set and clear a breakpoint at the desired location by pressing [F9]:

You can have as many breakpoints as you like in your program.

Assuming you have set breakpoints at three locations in your sketch:

Then you can watch your sketch passing the breakpoints in Visual Micro's Debug Window, including source file name and line, and a time stamp:

Start and Continue Your Sketch

You can choose if your sketch shall stop as it hits a breakpoint or if it shall continue to run (which is then called a tracepoint).

When using breakpoints (that keep the sketch halted), then you can measure signals on your hardware calmly, change anything on your hardware etc.

By pressing you can continue the execution of your sketch after it was halted in a breakpoint.

Viewing and changing variables

Knowing a variable's current value, can be essential for understanding your sketch's inner working.
The "classic method" of inserting Serial.print() calls is cumbersome. It's not enough to print a variable, you also need to add some descriptive text, so that you can tell all these numbers apart as they appear on your screen, that's why the typical test code looks like this:

With Visual Micro's debugger, you simply set a breakpoint, as shown above, and add a message string in the breakpoint's property window:

Visual Studio 2017 and 2019:

Visual Studio < 2017, 2019
and Atmel Studio:

While your sketch runs, you can watch how your variable's value changes in Visual Micro's Expression Window:

You will also see the min and max value your variable had.

Changing a variable's value

With Visual Micro, you can not only view variable values, you can also change them.
Whenever your Arduino sketch is halted in a breakpoint, you can change the variable's value shown in the Expression Window.

Additional Debugging Functionality

This is a list of additional functions Visual Micro offers for your Arduino debugging:

• Conditional breakpoints that only stop your sketch if a condition is met, e.g. a variable has a certain value
• Breakpoints with counters that stop your sketch only after a number of passes
• Enabling/Disabling breakpoints: You can activate or deactivate breakpoints with a click of your mouse, without building or uploading your sketch. The Breakpoint Window gives you an overview over all your breakpoints:
  
  
• Analog and Digital reporting windows: These windows show you the state of all analog and/or digital pins of your board.

This was a brief overview of the debugging capabilities of Visual Micro. Read the pages mentioned below to learn how to use them with your sketch: