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Cortex-M debugger for Python

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  • A new CI pipeline for functional tests is now running on a new test farm. Full results are publicly accessible on Azure Pipelines.
  • pyOCD has several new community resources: the website, a Slack workspace, and a mailing list for announcements.
  • Branch configuration changes: the default branch master has been renamed to main, and a develop branch has been added to be used for active development. New pull requests should generally target develop. See this discussion for more information about this change.

See the wiki news page for all recent news.

pyOCD is an open source Python based tool and package for programming and debugging Arm Cortex-M microcontrollers with a wide range of debug probes. It is fully cross-platform, with support for Linux, macOS, Windows, and FreeBSD.

A command line tool is provided that covers most use cases, or you can make use of the Python API to facilitate custom target control. A common use for the Python API is to run and control CI tests.

Support for more than 70 popular MCUs is built-in. In addition, through the use of CMSIS Device Family Packs, nearly every Cortex-M device on the market is supported.

The pyocd command line tool gives you total control over your device with these subcommands:

  • gdbserver: GDB remote server allows you to debug using gdb via either the console or several GUI debugger options.
  • load: Program files of various formats into flash or RAM.
  • erase: Erase part or all of an MCU's flash memory.
  • pack: Manage CMSIS Device Family Packs that provide additional target device support.
  • commander: Interactive REPL control and inspection of the MCU.
  • server: Share a debug probe with a TCP/IP server.
  • reset: Hardware or software reset of a device.
  • rtt: Stream Segger RTT IO with any debug probe.
  • list: Show connected devices.

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
  • SWO and SWV
  • and more!

Configuration and customization is supported through config files, user scripts, and the Python API.


  • Python 3.6.0 or later.†
  • macOS, Linux, Windows 7 or newer, or FreeBSD
  • A recent version of libusb. See libusb installation for details.
  • Microcontroller with an Arm Cortex-M CPU
  • Supported debug probe
    • CMSIS-DAP v1 (HID) or v2 (WinUSB), including:
      • Atmel EDBG/nEDBG
      • Atmel-ICE
      • Cypress KitProg3 or MiniProg4
      • DAPLink based debug probe, either on-board or standalone
      • Keil ULINKplus
      • NXP LPC-LinkII
      • NXP MCU-Link
    • PE Micro Cyclone and Multilink
    • Raspberry Pi Picoprobe
    • SEGGER J-Link
    • STLinkV2 or STLinkV3, either on-board or the standalone versions

† Version 0.29 is the last version to support Python 2.


PyOCD is beta quality.

The Python API is considered stable for version 0.x, but will be changed in version 1.0.


The pyOCD documentation is available on the website.

In addition to user guides, you can generate reference documentation using Doxygen with the supplied config file.


The full installation guide is available in the documentation.

For notes about installing and using on non-x86 systems such as Raspberry Pi, see the relevant documentation.

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

$ python3 -mpip install -U pyocd

Note: depending on your system, you may need to use python instead of python3.

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

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

$ python3 -mpip install --pre -U git+

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

$ python3 pip 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. On macOS, installing with sudo should never be required, although sometimes permissions can become modified such that installing without using sudo fails.
  2. Specify the --user option to install local to your user account.
  3. Run the command in a virtualenv local to a specific project working set.

udev rules on Linux

On Linux, particularly Ubuntu 16.04+, you must configure udev rules to allow pyOCD to access debug probes from user space. Otherwise you will need to run pyOCD as root, using sudo, which is very highly discouraged. (You should never run pyOCD as root on any OS.)

To help with this, example udev rules files are included with pyOCD in the udev folder. The readme in this folder has detailed instructions.

Target support

See the target support documentation for information on how to check if the MCU(s) you are using have built-in support, and how to install support for additional MCUs via CMSIS-Packs.

Using GDB

See the GDB setup documentation for a guide for setting up and using pyocd with gdb and IDEs.

Community resources

Join the pyOCD community! website
Mailing list for announcements

In order to foster a healthy and safe environment, we expect contributors and all members of the community to follow our Code of Conduct.


We welcome contributions in any area, even if you just create an issue. If you would like to get involved but aren't sure what to start with, just ask on Slack or GitHub discussions and we'll be happy to help you. Or you can look for an open issue. Any work on major changes should be discussed with the maintainers to make everyone is aligned.

Please see the contribution guidelines for detailed requirements. The developers' Guide has instructions on how to set up a development environment for pyOCD.

New pull requests should be created against the develop branch. (You have to change the "base" to develop.)


PyOCD is licensed with the permissive Apache 2.0 license. See the LICENSE file for the full text of the license. All documentation and the website are licensed with CC BY 4.0.

Copyright © 2006-2022 PyOCD Authors

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