Microcontroller Debugging: Understanding Debuggers

What is a Debugger?

A debugger is a tool used to test and debug code in real-time. It allows you to step through code, set breakpoints, and inspect internal states such as register values, memory content, and variable states, while the program is running on the microcontroller.

Types of Debuggers

• J-Link: A widely-used debugger developed by SEGGER, designed for ARM-based microcontrollers like STM32. It allows for real-time debugging and provides fast flash programming.
• Atmel ICE: A debugger from Microchip (formerly Atmel) that supports debugging for AVR and SAM (ARM Cortex-M) microcontrollers. It connects via the JTAG or SWD interface to enable hardware-level debugging.

How Debuggers Work

Debuggers work by interfacing between your development environment and the microcontroller. They provide access to internal states, allowing you to observe how the code executes line by line. A debugger usually connects via JTAG, SWD, or similar interfaces, depending on the microcontroller.

Key Features of Debuggers:

• Stepping Through Code: Execute code line by line to closely observe the flow and identify errors.
• Setting Breakpoints: Halt execution at specific lines of code to examine the state of variables, registers, or memory at that point.
• Inspecting Registers and Variables: Debuggers allow you to inspect and modify register values, watch variables, and monitor memory usage in real-time.

Example: Debugging with J-Link and STM32

Required Components

• 1x J-Link Debugger
• 1x STM32 microcontroller (e.g., STM32F103C8)
• 1x SWD (Serial Wire Debug) cable
• 1x IDE with debugging support (e.g., STM32CubeIDE)

Steps

1. Connect the J-Link to the Microcontroller: Use the SWD cable to connect the J-Link debugger to the SWD pins of the STM32 microcontroller (SWDIO, SWCLK, GND, VCC).
2. Open the IDE: Open STM32CubeIDE, where the source code and debugging options are available.
3. Start a Debugging Session: Load your project into the IDE. In the debug configurations, select the J-Link as your debugging tool. Start the session by clicking the debug button.
4. Set Breakpoints: Set breakpoints in your code by clicking in the left margin next to the line where you want to stop execution.
5. Step Through Code: Use the "Step Over" and "Step Into" buttons to go through your code line by line. The debugger will halt at each breakpoint, allowing you to examine variables and registers.
6. Inspect and Modify Variables: Use the variable or watch window to inspect the values of variables and registers. You can even modify them during runtime to test different scenarios.
7. Terminate Debugging: Once you have finished debugging, terminate the session. The program can then be allowed to continue running or reset for a new debug session.

Example: Debugging with Atmel ICE and AVR

Required Components

• 1x Atmel ICE Debugger
• 1x AVR microcontroller (e.g., ATmega328P)
• 1x JTAG or ISP cable
• 1x IDE with debugging support (e.g., Atmel Studio or MPLAB X)

Steps

1. Connect the Atmel ICE to the Microcontroller: Use the JTAG or ISP cable to connect the Atmel ICE debugger to the appropriate interface on your AVR microcontroller.
2. Open the IDE: Open Atmel Studio or MPLAB X, where you will have access to the debugging tools and options.
3. Start a Debugging Session: Load your AVR project into the IDE. Set up a debug configuration by selecting Atmel ICE as the debugger.
4. Set Breakpoints and Step Through Code: Set breakpoints by clicking in the margin next to the desired line of code. Step through the code using the “Step Into” or “Step Over” options to analyze the code execution flow.
5. Inspect Registers and Variables: Use the debugging window to inspect registers, variables, and memory in real-time. Modify variables as needed to observe different behaviors.
6. End Debugging: When you have completed your analysis, stop the debugging session, and allow the program to resume normal execution if required.