pyOCD

pyOCD is a Python-based GDB server supporting CMSIS-DAP compatible debug probes. It is the official debugger for Mbed and Mbed-enabled boards, and works well with many evaluation boards.

Installation

pip install pyocd

Or with pipx for isolated installation:

pipx install pyocd

Verify:

pyocd --version

Device Support Packs

pyOCD uses CMSIS packs for device-specific support. Install a pack for your target:

pyocd pack install stm32f4
pyocd pack install nrf52

List available targets:

pyocd list --targets

launch.json Configuration

{
  "type": "mcu-debug",
  "request": "launch",
  "name": "Debug (pyOCD)",
  "servertype": "pyocd",
  "executable": "${workspaceFolder}/build/firmware.elf",
  "targetId": "stm32f407vg"
}

Key Properties

Property	Description
targetId	pyOCD target identifier (e.g. stm32f407vg, nrf52840). Run pyocd list --targets for valid values.
boardId	Specific board to use when multiple are connected (the DAPLink board ID)
serverPath	Path to the pyocd binary if not on PATH
serverArgs	Extra command-line arguments to pyOCD

Connecting to a Specific Probe

If multiple CMSIS-DAP probes are connected:

"serverArgs": ["--uid", "0240000034544e45001700068084e4e600000000097969900"]

Find UIDs with:

pyocd list

Common Issues

"No connected probes"

• Probe is not connected, not recognized, or requires udev rules (Linux)
• On Linux: install CMSIS-DAP udev rules. Many Linux distributions include them, or install the libusb dev package.

Target not supported

pyocd pack install <target>

Or check the available targets:

pyocd pack find <partial-name>