5 Most Used Debugging Techniques in Embedded Firmware

  • February 07, 2025

Introduction

Debugging embedded firmware is a unique challenge due to tight hardware-software integration. Unlike PC software, embedded systems have limited resources (memory, processing power) and rely on real-time operations. Errors can stem from code, hardware faults, or timing mismatches.

Common techniques include JTAG/SWD for step-by-step code inspection, UART for real-time monitoring, and logic analyzers to debug communication buses. Each method has its own drawbacks hardware debuggers offer precision but require physical access, while printf logging is simple but slows execution.

1. JTAG/SWD Debugging

Hardware interfaces for real-time debugging. JTAG (Joint Test Action Group) and SWD (Serial Wire Debug) allow direct control over the microcontroller.

How to use JTAG/SWD?

  • Set breakpoints in your IDE (e.g., STM32CubeIDE) to pause code execution.
  • Inspect registers, memory, and peripheral states during pauses.
  • Step through code line-by-line to track logic errors.

Pros of JTAG/SWD:

  • Non-intrusive to code.
  • Deep hardware-level insights

Cons of JTAG/SWD:

  • Limited breakpoints (varies by chip).
  • Can disrupt real-time behavior.

2. Serial Output (UART)

Transmitting debug messages via UART to a terminal.

How to use UART?

  • Embed printf statements to log variables, states, or errors.
  • Monitor logs using tools like PuTTY or Tera Term.

Pros of UART:

  • Simple to implement.
  • Works on most microcontrollers

Cons of UART:

  • Slows down execution.
  • Not ideal for timing-sensitive systems.

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3. Logic Analyzers & Oscilloscopes

Tools to analyze digital/analog signals on buses like SPI, I2C, or UART.

How to use logic analyzers & oscilloscopes ?

  • Probe communication lines (e.g., clock, data).
  • Use protocol decoding to spot errors in transmitted data.
  • Best for: Diagnosing signal noise, timing mismatches, or protocol violations

Tools

  • Logic Analyzers: Saleae, DSLogic
  • Oscilloscopes: Keysight, Rigol

4. Real-Time Trace Analysis :

Recording execution flow, interrupts, and task switches in real-time.

How to use real time trace analysis?

  • Enable Embedded Trace Macrocell (ETM) on chips like STM32.
  • Analyze traces using tools like Percepio Tracealyzer.

Pros of real time trace analysis:

  • Identifies race conditions and task starvation in RTOS24.

Cons of real time trace analysis:

  • Requires compatible hardware/software.

5. Watchdog Timers

A timer that resets the system if firmware freezes.

How to use watchdog timers:

  • Periodically kick the timer in stable code sections.
  • Debug unexpected resets to locate crashes.

Conclusion

Debugging embedded firmware demands patience, systematic thinking, and the right tools. Start by isolating the problem—test individual hardware components and code modules before integration. Use JTAG/SWD to inspect registers and set breakpoints, but avoid overloading the system with too many breakpoints. For communication errors, logic analyzers help spot signal glitches or protocol violations. Always cross-check hardware (e.g., voltage levels, connections) before blaming the code.

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