Skip to main content

Cortex-M debugger for Python

Project description


pyOCD is an open source Python package for programming and debugging Arm Cortex-M microcontrollers using multiple supported types of USB debug probes. It is fully cross-platform, with support for Linux, macOS, and Windows.

Several command line tools are provided that cover most use cases, or you can make use of the Python API to enable low-level target control. A common use for the Python API is to run and control CI tests.

Three tools give you total control over your device:

  • pyocd-gdbserver: GDB remote server allows you to debug using gdb via either GNU MCU Eclipse plug-in or the console.
  • pyocd-flashtool: Program and erase an MCU's flash memory.
  • pyocd-tool: Interactive REPL control and inspection of the MCU.

The API and tools provide these features:

  • halt, step, resume control
  • read/write memory
  • read/write core registers
  • set/remove hardware and software breakpoints
  • set/remove watchpoints
  • write to flash memory
  • load binary, hex, or ELF files into flash
  • reset control
  • access CoreSight DP and APs
  • and more!


  • Python 2.7.9 or later, or Python 3.6.0 or later
  • macOS, Linux, or Windows 7 or newer
  • Microcontroller with an Arm Cortex-M CPU
  • Supported debug probe
    • CMSIS-DAP, such as an on-board debug probe using DAPLink firmware.
    • STLinkV2, either on-board or the standalone version.


PyOCD is functionally reliable and fully useable.

The API is considered unstable because we are planning some breaking changes to bring the naming convention into compliance with PEP8 prior to releasing version 1.0. We also plan to merge the three command line tools into a single tool.


The pyOCD documentation is located in the docs directory.


The latest stable version of pyOCD may be installed via pip as follows:

$ pip install -U pyocd

The latest pyOCD package is available on PyPI as well as on GitHub.

To install the latest prerelease version from the HEAD of the master branch, you can do the following:

$ pip install --pre -U

You can also install directly from the source by cloning the git repository and running:

$ python install

Note that, depending on your operating system, you may run into permissions issues running these commands. You have a few options here:

  1. Under Linux, run with sudo -H to install pyOCD and dependencies globally. (Installing with sudo should never be required for macOS.)
  2. Specify the --user option to install local to your user.
  3. Run the command in a virtualenv local to a specific project working set.

libusb installation

pyusb and its backend library libusb are dependencies on all supported operating systems. pyusb is a regular Python package and will be installed along with pyOCD. However, libusb is binary shared library that does not get installed automatically via pip dependency management.

How to install libusb depends on your OS:

  • macOS: use Homebrew: brew install libusb
  • Linux: should already be installed.
  • Windows: download libusb from and place the DLL in your Python installation folder next to python.exe.

udev rules on Linux

If you encounter an issue on Linux where pyocd-tool list won't detect attached boards without sudo, the reason is most likely USB device access permissions. In Ubuntu 16.04+ these are handled with udev and can be solved by adding a new udev rule.

An example udev rule file is included in the udev folder in the pyOCD repository. Just copy this file into etc/udev/rules.d to enable user access to both DAPLink-based debug probes as well as STLinkV2 and STLinkV3.

If you use different, but compatible, debug probe, you can check the IDs with dmesg command.

  • Run dmesg
  • Plug in your board
  • Run dmesg again and check what was added
  • Look for line similar to usb 2-2.1: New USB device found, idVendor=0d28, idProduct=0204

Standalone GDB server

When you install pyOCD via pip or, you will be able to execute the following in order to start a GDB server powered by pyOCD:

$ pyocd-gdbserver

You can get additional help by running pyocd-gdbserver --help.

Example command line GDB session showing how to connect to a running pyocd-gdbserver and load firmware:

$ arm-none-eabi-gdb application.elf

<gdb> target remote localhost:3333
<gdb> load
<gdb> monitor reset

The pyocd-gdbserver executable is also usable as a drop in place replacement for OpenOCD in existing setups. The primary difference is the set of gdb monitor commands.

Recommended GDB and IDE setup

The GDB server works well with Eclipse and the GNU MCU Eclipse plug-ins. GNU MCU Eclipse fully supports pyOCD with an included pyOCD debugging plugin.

To view peripheral register values either the built-in GNU MCU Eclipse register view can be used, or the Embedded System Register Viewer plugin can be installed. These can be installed from inside Eclipse using the following software update server addresses:

In Eclipse, select the "Help -> Install New Software…" menu item. Then either click the "Add…" button and fill in the name and URL from above (once for each site), or simply copy the URL into the field where it says "type or select a site". Then you can select the software to install and click Next to start the process.

Development setup

Please see the Developers' Guide for instructions on how to set up a development environment for pyOCD.


We welcome contributions to pyOCD in any area. Please see the contribution guidelines for details.

To report bugs, please create an issue in the GitHub project.


PyOCD is licensed with Apache 2.0. See the LICENSE file for the full text of the license.

Copyright © 2006-2018 Arm Ltd

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
pyocd-0.14.0.tar.gz (1.0 MB) Copy SHA256 hash SHA256 Source None

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN SignalFx SignalFx Supporter DigiCert DigiCert EV certificate StatusPage StatusPage Status page