Adafruit's CircuitPython is an open-source implementation of Python for microcontrollers. It's derived from (also known as, a "fork" of) MicroPython, a ground-breaking implementation of Python for microcontrollers and constrained environments.

CircuitPython ships on many Adafruit products. We regularly create new releases and make it easy to update your installation with new builds.

However, you might want to build your own version of CircuitPython. You might want to keep up with development versions between releases, adapt it to your own hardware, add or subtract features, or add "frozen" modules to save RAM space. This guide explains how to build CircuitPython yourself.

CircuitPython is meant to be built in a POSIX-style build environment. We'll talk about building it on Linux-style systems or on macOS. It's possible, but tricky, to build in other environments such as CygWin or MinGW: we may cover how to use these in the future.

Install a Real or Virtual Linux Machine

If you don't already have a Linux machine, you can set one up in several different ways. You can install a Linux distribution natively, either on its own machine or as a dual-boot system. You can install Linux on a virtual machine on, say, a Windows host machine. You can also use Windows Subsystem for Linux (WSL), available on Microsoft Windows 10, which allows you to run a Linux distribution with an emulation layer substituting for the Linux kernel.

We recommend using the Ubuntu distribution of Linux or one of its variants (Kubuntu, Mint, etc.). The instructions here assume you are using Ubuntu. The 22.04 LTS (Long Term Support) version is stable and reliable.

Native Linux

You can install Ubuntu on a bare machine easily. Follow the directions on the Ubuntu website. You can also install Ubuntu on a disk shared with your Windows installation, or on a separate disk, and make a dual-boot installation.

Linux on a Virtual Machine

Linux can also be installed easily on a virtual machine. First you install the virtual machine software, and then create a new virtual machine, usually giving the VM software a .iso file of Ubuntu or another distribution. On Windows, VM Workstation Player and VirtualBox are both free and easily installed. Malke your virtual machine filesystem at least 20GB so you won't run out of space.

Raspberry Pi

It may be possible to build on Raspberry Pi OS, but it will be easier if you install Ubuntu on your Raspberry Pi. You will also need to download the aarch64 gcc toolchain. The RPi is not a fast machine: be prepared to wait for a build to complete.

Install Build Tools on Ubuntu

The Ubuntu 22.04 LTS Desktop distribution includes most of what you need to build CircuitPython. You'll need to install some additional packages, including build-essential, if it's not already installed, and also git, git-lfs, gettext, uncrustify, and cmake.

The version of git (2.30) installed with Ubuntu 22.04 will work, but git versions that support partial submodule cloning (2.36 or later) will work better with submodules.

In a terminal window, do:

Cortex-M Builds

Most CircuitPython boards use an ARM Cortex-M processor.  You need to download and unpack the appropriate ARM Cortex-M toolchain. Do not use the obsolete ARM Ubuntu "ppa" (private package archive). The links below point to the general download pages for the toolchains. Choose the arm-none-eabi version of the compiler, and select the correct architecture for your development computer, such as x64 Linux for a typical Linux PC. The package library for your particular Linux distribution will not necessary install the correct version.

• For CircuitPython 6.1, 7.x, and 8.x, use the 10-2020-q4-major version.
• For CIrcuitPython 9.x, use the 13.2.Rel1 version.

If you want to build an older version of CircuitPython:

• For CircuitPython 5 and 6.0, use the  9-2019-q4-major version.
• CircuitPython 4 was built with the 7-2018q2-update version.

Cortex-A Builds

The broadcom port (Raspberry Pi Linux boards) needs a different toolchain. Use the Cortex-A toolchain:

• For CircuitPython 7.x and later, use the 10.3-2021.07 version.

You will also need the mtools package:

And finally, you need a version 4.2 or later of mkfs.fat, which is part of the dosfstools package. Ubuntu 20.04 has version 4.1. You can download and build dosfstools. After you do so, copy mkfs.fat to some place that is or will be on your PATH.

Installing the Toolchain

Unpack the toolchain in a convenient directory.

Next, add a line to your .bash_profile or other startup file to add the unpacked toolchain executables to your PATH. For example:

Open a new terminal window, and see if you now have the correct executables on your path:

Other Builds

• For Espressif (ESP32-S2, -S3, -C3), see the Espressif build page.
• For Spresense (cxd56), see the cxd56 README.
• For Litex (FOMU), see the litex README.

Now move to the Build CircuitPython section of this guide. There we will get the CircuitPython source code, install a few more dependencies, and then build!

To build CircuitPython on macOS, you need to install git, python3, and the compiler toolchain. The easiest way to do this is to first install Homebrew, a software package manager for macOS. Follow the directions on its webpages.

Now install the software you need:

Then install the compiler toolchain. You can use  the gcc-arm-embedded homebrew formula to install the correct toolchain, but make sure you have homebrew install the correct version, as described on the Linux Setup page in this guide. As an alternative to homebrew, on the Linux Setup page, you can find pointers to the download pages for different kinds of ARM processors, and also special instructions for other builds (not all are available on macOS). Download and install the appropiate .pkg file for your Mac.

Once the dependencies are installed, we'll also need to make a disk image to clone CircuitPython into. By default the macOS filesystem is case insensitive. In a few cases, this can confuse the build process. So, we recommend creating a case sensitive disk image with Disk Utility to store the source code. Make the image capable of storing at least 10GB, preferably 20GB, so you won't run out of space if you do extensive development. You can use a sparse bundle disk image which will grow as necessary, so you don't use up all the space at once. The disk image is a single file that can be mounted by double clicking it in the Finder. Once it's mounted, it works like a normal folder located under the /Volumes directory.

Install gmake if Necessary

Depending on your version of macOS, whether or not you have installed Xcode, and other factors, the version of make on your Mac may not be recent enough to run builds. Check the version:

If neither program exists, or both are older than version 4.3, install a newer version of gmake with brew:

If you install the brew version of make, it will be known as gmake.

That's it! Now you can move on and actually Build CircuitPython. There we will get the CircuitPython source code, install a few more dependencies, and then build!

Windows Subsystem for Linux (WSL) is a feature of Windows 10 that lets you run Ubuntu and other versions of Linux right in Windows. It's real Ubuntu, without the Linux kernel, but with all the software packages that don't need a graphical interface. You can build CircuitPython in WSL easily. It's easier to install than a Linux virtual machine.

Install WSL

The installation procedures for WSL continue to evolve. Rather than provide information here which quickly becomes outdated, we ask that you refer to Microsoft's official instructions: Windows Subsystem for Linux Installation Guide for Windows 10. Enable WSL 2, which is better for our purposes than WSL 1 in several ways.

Note that your PC must have hardware virtualization support. Virtualization must also be enabled in the BIOS OR UEFI.

One WSL 2 is set up, you need to choose a Linux distribution to install, as described in the document above. Choose Ubuntu 22.04, or if not immediately available, install 20.04, and optionally upgrade to 22.04.

Finish Linux Install

Once WSL is set up, just proceed with the regular Linux Setup.

Build CircuitPython

From this point on, you can build CircuitPython just as it's built in regular Ubuntu, described in the Build CircuitPython section of this guide.

Moving Files to Windows

You can copy files to and from Windows through the /mnt/c. For instance, if you want to copy a CircuitPython build to the desktop, do:

You might be tempted to clone and build CircuitPython in a folder shared with the Windows filesystem (in /mnt/c somewhere). That can cause problems, especially if you use git commands on the Windows side in that folder. The CircuitPython build assumes case-sensitive filenames, but Windows usually ignores filename case differences. You may also have line-ending problems (CRLF vs.  LF). It's better to clone and build inside your home directory in WSL, and copy files over to a shared folder as needed. It is possible to drag and drop files between WSL and Windows.

Mounting a CircuitPython Board in WSL

You can mount your ...BOOT or CIRCUITPY drive in WSL. Create a mount point and then mount it. Note that you'll have to remount each time the drive goes away, such as when you restart the board or switch between the BOOT drive and CIRCUITPY. So it's probably more convenient to copy files to the board from Windows instead of WSL.

Editing Files in WSL

You can use the usual Linux editors in WSL, such as vim and emacs. You may need to install them explicitly. Visual Studio Code (not Visual Studio) is also available: do a websearch to find the latest instructions. Visual Studio Code in Windows has a WSL extension.

If the setup instructions above don't work for your particular OS setup, for whatever reason, you can get the ball rolling by installing these tools in whatever way you can and then getting them to work with the Makefile in circuitpython/ports/atmel-samd. (main branch):

• git
• git-lfs
• make
• python3
• gettext
• cmake
• All Python packages listed in requirements-dev.txt. You will need to clone the repository to see that file.
• ARM gcc toolchain for Cortex-M boards: https://developer.arm.com/open-source/gnu-toolchain/gnu-rm/downloads
• ARM gcc toolchain for Cortex-A boards (only needed for broadcom port): https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-a/downloads
  See information about which gcc version to pick on the Linux Setup page of this guide.

The build setup and steps in this guide change frequently, and are updated as needed. If you are are having trouble, check this page, which highlights recent changes, to see if you need to update your build environment. The changes mentioned here are also documented in the other pages in this guide.

Install git-lfs

git-lfs is now a required prerequisite, as of CircuitPython 8.1.0. The submodules in the silabs port require it.

Fetching Submodules

Submodules should be fetched using the Makefile targets fetch-all-submodules,  which is in the top-level Makefile, or fetch-port-submodules, which is used from port-specific Makefiles. If you use standard git commands for fetching submodules, you will end up fetching many gigabytes of unnecessary versions.

See this page section for more details.

These make targets do either a partial "blobless" clone of all submodules, if your version of git supports it, or else does a shallow depth 1 clone.

make remove-all-submodules removes all submodules and cleans up, so you can do a fresh make fetch-all-submodules or fetch-port-submodules. Use make remove-all-submodules if you are getting errors when fetching submodules.

These Makefile targets were added June 6, 2023, changing a previous target, added in late March, 2023 that only fetched all modules, make fetch-submodules.

Fetch the Code to Build

Once your build tools are installed, fetch the CircuitPython source code from its GitHub repository ("repo") and also fetch the git "submodules" it needs. The submodules are extra code that you need that's stored in other repos.

In the commands below, you're cloning from Adafruit's CircuitPython repo. But if you want to make changes, you might want to "fork" that repo on GitHub to make a copy for yourself, and clone from there. For more information about using GitHub and forking a repo, see the Contribute to CircuitPython with Git and GitHub guide.

Install Required Python Packages

After you have cloned the repo, you'll need to install some Python packages that are needed for the build process. You only need to do this the first time, though you may want to run this again from time to time to make sure the packages are up to date.

The --upgrade flag will force installation of the latest packages, except where a version is explicitly specified in the requirements-*.txt files.

If you get an error indicating that rust is needed to install minify-html, install rust:

Checking out a Specific Branch or Version

If you want to build a version other the latest, checkout the branch or tag you want to build. For example:

Note the build process has evolved, and earlier versions will need to be built somewhat differently than how the instructions in this guide specify. If you have trouble, ask on Discord or the forums.

Fetch Submodules

We are not using git submodule update --init --recursive or git submodule update --init. Instead you run the special Makefile target make fetch-all-submodules at the top level, or make fetch-port-submodules when you in a particular ports/port-name directory. The target fetches only as many commits from each submodule as is necessary, using either a blobless partial clone (if available) or a shallow clone. This saves downloading the complete trees of some large submodules.

make fetch-all-submodules fetches all the submodules in the entire repository, and can take several minutes and use up a lot of storage. If you are planning to build only in one or a few port directories, you'll save time by using make fetch-port-submodules, which fetches only the submodules need for that particular port.

If you are having trouble with your submodules, you can clean out all the fetched modules by doing make remove-all-submodules at the top level. Then run make fetch-all-submodules or make fetch-port-submodules again to fetch a fresh copy of all the submodules. (There is no make remove-port-submodules.)

Using a Version of git that can do Partial Clones

As mentioned above, the submodule fetching targets try to do a blobless partial clone if possible. This is better than a shallow clone: it is slightly faster, and the partial clone acts like a full clone if you want to maneuver around in the submodule by checking out other commits, examining the history, etc.

Git version 2.36 or later supports blobless partial clones. To find out which version of git you are using, do git --version. Consider installing a newer version of git if it is available. On Ubuntu, you can install the git PPA and get the latest stable version of git. On macOS, homebrew may provide a later version for you.

Install pre-commit

We are using the pre-commit system to check submitted code for problems before it gets to GitHub. For more information, see this Learn Guide page. To add pre-commit to your repository clone, do:

Build mpy-cross

Build the mpy-cross compiler first, which compiles Circuitpython .py files into .mpy files. It's needed to include library code in certain boards.

(If you get a make: msgfmt: Command not found error, you have not installed gettext. Go back to the Setup page for your operating system.)

Normally you do not need to rebuild mpy-cross on every pull or merge from the circuitpython repository or for your own changes. The .mpy format does not change very often. But occasionally when we merge from MicroPython, the format changes. You will find that your old .mpy files or frozen libraries give an error, and you will need to rebuild mpy-cross.

Build CircuitPython

Now you're all set to build CircuitPython. If you're in the main branch of the repo, you'll be building the latest version. Choose which board you want to build for. The boards available are all the subdirectories in ports/atmel-samd/boards/.

By default the en_US version will be built. To build for a different language supply a TRANSLATION argument.

Run Your Build!

When you've successfully built, you'll see output like:

Copy firmware.uf2 to your board the same way you'd update CircuitPython: Double-click to get the BOOT drive, and then just copy the .uf2 file:

The board will restart, and your build will start running.

If you're using a board without a UF2 bootloader, you'll need to use bossac and the firmware.bin file, not the .uf2 file. Detailed instructions are here.

Use All Your CPUs When Building

Most modern computers have CPU chips with multiple cores. For instance, you may have a 2-core, 4-core, or 6-core or more CPU. Your CPU may also allow 2 "threads" per core, so that it appears to have even more cores. You can run much of the build in parallel by using the make -j flag. This is will speed up the build noticeably.

If you don't know how many cores or threads your CPU has, on Linux you can use this command:

Then, when you run make, add the -j<n> option to use as many cores or threads as possible. For example:

When to make clean

After you make changes to code, normally just doing make BOARD=... will be sufficient. The changed files will be recompiled and CircuitPython will be rebuilt.

However, there are some circumstance where you must do:

If you have changed the #include file structure in certain ways, or if you have defined QSTR's (a way of defining constants strings in the CircuitPython source), then you must make clean before rebuilding. If you're not sure, it's always safe to make clean and then make. It might take a little longer to build, but you'll be sure it was rebuilt properly.

Updating Your Repo

When there are changes in the GitHub repo, you might want to fetch those and then rebuild. Just "pull" the new code (assuming you haven't made changes yourself), update the submodules if necessary, and rebuild:

Those are the basics. There's a lot more to know about how to keep your forked repo up to date, merge "upstream" (Adafruit's) changes into your code, etc. We cover this in the Contribute to CircuitPython with Git and GitHub guide

Normally, all imported Python modules in CircuitPython are loaded into RAM in compiled form, whether they start as .mpy or .py files. Especially on M0 boards, a user program can run out of RAM if too much code needs to be loaded.

To ameliorate this problem, a CircuitPython image can include compiled Python code that is stored in the image, in flash memory, and executed directly from there. These are "internal frozen modules". The circuitplayground_express  builds use this technique, for example.

If you would like to build a custom image that includes some frozen modules, you can imitate how it's done in the circuitplayground_express build. Look at boards/circuit_playground_express/mpconfigboard.mk:

Notice the FROZEN_MPY_DIRS lines in the file. Pick the mpconfigboard.mk file for the board you are using, and add one or more similar lines. You will need to do add directories for the libraries you want to include. If these are existing libraries in GitHub, you can add them as submodules. For instance, suppose you want to add the Adafruit_CircuitPython_HID library to the feather_m0_express build. Add this line to boards/feather_m0_express/mpconfigboard.mk:

Then add the library as a submodule:

When you add the submodule it will be cloned into the frozen/ directory.

Set the submodule to a commit that is a release tag. If you try to freeze a module that is at untagged commit, you'll get a git error when building. You can update all the frozen modules to the latest release tags by doing this, at the top level of your repository clone:

Alternatively, simply check out a tagged version of the submodule after you add the submodule and before you commit it:

Note that there is limited unused space available in the images, especially in the non-Express M0 builds, and you may not be able to fit all the libraries you want to freeze. You can of course try to simplify the library code if necessary to make it fit.

CircuitPython supports external SPI/QSPI flash chips for the CIRCUITPY filesystem. Each board build is setup to support only one or a few flash chips. The chips are not identical in how they are accessed, so you can't just substitute without rebuilding. The chips that CircuitPython currently supports are listed in a GitHub repository of chip data, https://github.com/adafruit/nvm.toml, along with the settings needed for each.

The chip(s) that are supported in a particular board are specified in the mpconfigboard.mk file for that board, in the line that defines EXTERNAL_FLASH_DEVICES.  So change or add to EXTERNAL_FLASH_DEVICES if you want to use a different supported chip. We don't support a entire list of chips for each build because the table of data for all possible chips would take significant space in the CircuitPython build.

Here's an example:

You may want to include a particular module that is not included by default for the board for your board. You can customize which modules to include in your CircuitPython build by adding or changing settings in the mpconfigboard.mk file for your board.

For example, here is the standard circuitpython/ports/atmel-samd/boards/trinket_m0/mpconfigboard.mk file:

Suppose you wanted to turn on pulseio, but you did not need MIDI support. There is not enough room for pulseio in this build, but if you turn other modules, you can make room. Sometimes this will work only for certain languages due to the size of the translation. In this case, for the en_US translation, turning off usb_midi frees up enough space to include pulseio. Add these lines to the file above:

You can figure out which modules are on or off by looking at the module support matrix in the CIrcuitPython documentation. It also helps to study the files circuitpython/py/circuitpy_mpconfig.mk and circuitpympconfig.h, and circuitpython/ports/<your-board's-port>/mpconfigport.mk and mpconfigport.h.

Warning: Don't put Makefile comments on the same line as Makefile assignments. I causes the variable value to include the trailing spaces before comment character. 

The ports/espressif build setup is a rather involved process. Please read the README.md in that directory. It has instructions that also refer to further instructions in the ESP-IDF documentation.

On MacOS, you will need to install cmake and ninja:

On Linux you probably need to install ninja-build and cmake.

The ESP-IDF expects there to be a python command which runs python3. On Ubuntu, there is no plain python by default, so install this simple package which links python to python3.

Once you have the prerequisites installed, change to the ports/espressif directory, and run the install.sh script. You only need to do this once.

After this, in each fresh terminal window in which you are doing builds, you need to use esp-idf/export.sh in order to set up the correct PATH and other environment variables.

export.sh will suggest that you use idf.py to do a build after you run it. But we don't use idf.py. Instead, use make, for example:

You will need to repeat the pip3 install commands described here so that they take effect inside the Python environment set up by source esp-idf/export.sh. But you will need to do this only once.