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2. How OpenCD and SWD work?

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Andrea ZGuz edited this page Dec 26, 2023 · 1 revision

What is OpenOCD?

OpenOCD stands for Open On-Chip Debugger, and it's an open-source software tool used for debugging and interacting with embedded systems. Essentially, it acts as a bridge between your computer and the microcontroller or other embedded device you're working with.

What OpenOCD do?

  • Provides debugging capabilities: You can set breakpoints, step through code, and examine variables in real-time to understand how your embedded program is running.
  • Enables in-system programming (ISP): You can flash new firmware or software onto your device directly from your computer without removing any chips.
  • Supports boundary-scan testing: This advanced technique allows you to test the physical connections and components on your device's circuit board.

Some of the benefits of using OpenOCD:

  • Free and open-source: You can download and use OpenOCD for free, and you have access to the source code to modify it for your specific needs.
  • Supports a wide range of devices: OpenOCD works with various microcontrollers and other embedded devices from different manufacturers.
  • Powerful and versatile: OpenOCD offers a wide range of features that can be used for various debugging and programming tasks.

OpenOCD works alongside a debug adapter (DAP Cat programmer, in this case) that connects your computer to the target embedded system.

Manual available

Serial Wire Debug (SWD) protocol

SWD is a two-wire interface used to debug microcontrollers with ARM processors. It's a simpler and more cost-effective alternative to the traditional JTAG interface, which requires four or five wires.

Here's how SWD works:

Hardware:

  • Two pins: SWDIO (data) and SWCLK (clock). An optional third pin, SWO, can be used for trace data.
  • Debug probe: Connects to the SWD pins and communicates with the debugger software on your computer.

Communication:

  • Serial protocol: Data is transferred bit by bit over the SWDIO pin, synchronized by the SWCLK signal.
  • Master-slave relationship: The debug probe acts as the master, initiating communication and controlling the data flow. The microcontroller acts as the slave, responding to the probe's commands.
  • ARM Debug Interface (ADI): Defines the commands and responses used for communication. This ensures compatibility with various debug tools and microcontrollers.

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