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Cortex Debug

Visual Studio Code with Cortex-Debug Installed

Debugging support for ARM Cortex-M Microcontrollers with the following features:

  • Highly configurable. See
  • Support J-Link, OpenOCD GDB Server, STMicroelectronic's ST-LINK GDB server (no SWO support yet), pyOCD
  • Initial support for the Black Magic Probe (This has not been as heavily tested; SWO can only be captured via a serial port)
  • Partial support textane/stlink (st-util) GDB Servers (SWO can only be captured via a serial port)
  • Multi-core and multi-session debugging. See
  • Disassembly of source code available along with instruction level breakpoints and stepping. The actual disassembly window is provided and managed by VSCode. See
  • Cortex Core Register Viewer (integrated into Variables window since V1.2)
    • In some cases the st-util GDB server can report incomplete/incorrect registers, so there may be some issues here.
  • SWO Decoding - "console" text output and binary data (signed and unsigned 32-bit integers, Q16.16 fixed point integers, single precision floating point values)
    • The registers that are part of the DWT, TPIU, and ITM debug components will automatically be configured and do not need to be set in firmware.
    • Firmware may still need to enable the SWO output pin - as this part of the setup is microcontroller dependant.
    • Decoding ETM data over the SWO pin is not currently supported.
  • Live graphing of decoded ITM data.
  • Support for Custom ITM Data Decoders:
    • Ability to define JavaScript modules to decode complex data formats streamed over one or more ITM ports. Data can be printed to a output window, or sent to the graphing system. If you are using TCP/IP instead, you can use a variety of tools to connect to the that port.
  • Semi-hosting Support. In the TERMINAL tab, there will be a sub-window called gdb-server. That terminal is bidirectional and is intended for semi-hosting. This applies to those gdb-servers that do their semi-hosting on their stdio.
  • Support for SEGGER Real Time Trace (RTT) using OpenOCD and J-Link gdb-servers. All the features supported for SWO (text, binary, graphing) are also supported with RTT. See image above for console style output. SWO output also creates another section.
  • Globals and Static scopes in the variables view
  • Initial support for Rust code (most functionality is working; report any issues
  • RTOS Thread Support in CALL STACK window (J-Link, OpenOCD, pyOCD - RTOS supported depend on GDB server)
    • As a general rule do not try to use stepping instructions before the scheduler of your RTOS has started - in many cases this tends to crash the GDB servers or leave it in an inconsistent state.
  • Live Watch with supported GDB servers (tested with OpenOCD, J-Link, STLink so far - since V1.6)
  • We have a set of extensions that this extension relies on for various frontend services (since V1.6)

Release Versioning

Cortex-Debug uses a versioning system specified by Microsoft that allows distribution of pre-releases via the marketplace. You can enable (or disable) pre-releases within VSCode for this extension and you will automatically get new pre-releases. By default, pre-releases are disabled. We use pre-releases as allow testing of bug fixes and new features. They allow you participate during the formation of a feature of how an issue gets addressed. More info about pre-releases. To summarize, extensions use semantic versioning (SemVer) system which in simple terms is major.minor.patch. With MS convention, if the minor version is odd, then it is a pre-release.

Planned Features



  • ARM GCC Toolchain ( - provides arm-none-eabi-gdb and related tools
  • At least one of:
    • J-Link Software Tools - provides the J-Link GDB Server for J-Link based debuggers (
    • OpenOCD - provides a GDB Server that can be used with a number of debuggers (
      • NOTE: If a chip vendor ships it's own OpenOCD version, for sure use NOTHING but that
      • NOTE: On macOS do not use the default version of OpenOCD provided by homebrew, this is not compatible with releases V0.2.4 and newer.
      • NOTE: Some linux versions and Windows may also need a more up-to-date version of OpenOCD from the xPack releases.
    • Texane's st-util GDB server - Only supports ST-Link Debug Probes (
    • ST-LINK GDB server - This server is packaged with the STM32CubeIDE which must be installed. The location of the STM32CubeIDE and related tools is automatically resolved but also can be overridden using configuration settings (armToolchainPath, stm32cubeprogrammer and serverpath).
    • pyOCD GDB Server - GDB server that supports the CMSIS-DAP debugger on a number of mbed boards (
    • Black Magic Probe


See for usage information. This needs some help from the community. See for a summary of all properties that are available in your launch.json

How to Build from sources

  • git clone
  • cd cortex-debug
  • Optionally switch to a branch: git checkout <existing-branch-name>
  • npm install
  • Optional npm run compile
  • Open VSCode in the top folder and run the task npm watch. This will compile the code and watch for any changes and auto compile. The first time, it may take a minute or so for it to watch the entire folder. You can see the output of npm watch in the Terminal tab.

How to debug

The extension is split into two main parts.

  1. The front-end which is what you interact with mostly
  2. The backend called debug adapter which interfaces between gdb, vscode/front-end, and the gdb-server. We just start the server and from then on the debug adapter only interacts with gdb. All requests go to gdb and the results are read back from gdb using gdb's MI (machine interface)

If you want to debug both parts, in launch.json use the Extension + Debug Server configuration. It will launch a new window -- the debuggee. In the debuggee VSCode window, load a FW folder/workspace (VSCode remembers the last one) and add the following to debuggee's launch.json.

            "debugServer": 4711

Now, launch a debug session and you wil be able to use the primary VSCode window to observe the Cortex-Debug extension


Parts of this extension are based upon Jan Jurzitza's (WebFreak) code-debug extension (
His project provided an excellent base for GDB MI parsing and interaction.