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 20.04 LTS (Long Term Support) version is stable and reliable.

Native Linux

You can install Ubuntu on a bare machine easily. Follow the directions (this link is for 20.04) 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.


Vagrant is software that is designed to make it easy to set up and use pre-configured virtual machines. There are potential stumbling blocks. This guide will include Vagrant information in the future.

Install Build Tools on Ubuntu

The Ubuntu 20.04 LTS Desktop distribution includes most of what you need to build CircuitPython. First, in a terminal window, do:

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sudo apt update
# Try running `make`. If it's not installed, do:
# sudo apt install build-essential
sudo apt install git
sudo apt install gettext
pip3 install huffman

Next you need to download and unpack the ARM gcc toolchain from its download page. ARM is no longer updating its Ubuntu "ppa" (private package archive), so you need to install these manually.

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# Put the unpacked toolchain into an appropriate directory.
# This is an example.
cd ~/bin
tar xvf <name of the .bz2 file you downloaded>

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

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export PATH=/home/$USER/bin/gcc-arm-none-eabi-9-2019-q4-major/bin:$PATH

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

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$ which arm-none-eabi-gcc

Now move to the Build CircuitPython section of this guide.

To build CircuitPython on MacOS, you need to install git, python3, and the ARM 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:

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brew update
brew install git python3 gettext
brew link gettext --force
pip3 install huffman

And finally, install the ARM toolchain (note that cask is no longer necessary). As of late December 2020, this installs a gcc10-based toolchain (see the Linux Setup page in this guide for more information about gcc versions).

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brew install gcc-arm-embedded

Once the dependencies are installed, we'll also need to make a disk image to clone CircuitPython into. By default the Mac OSX 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, 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.

That's it! Now you can move on and actually Build CircuitPython.

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. The filesystem access is slower than on regular Linux, so builds will take somewhat longer, but it's quite usable.

Install WSL

To install WSL, you need to be running a recent version of 64-bit Windows 10. Go to Control Panel > Programs >Windows Features, and check the box for Windows Subsystem for Linux.

After that, you'll have to reboot Windows. After it's rebooted, go to the Microsoft Store, search for Ubuntu, and install it.

Then launch Ubuntu. You'll see a terminal console window and you'll be asked some initial setup questions.

Install Build Tools

This step is the same as for regular 18.04 Ubuntu, so refer to that page, and then come back here.

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:

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cp build-circuitplayground_express/firmware.uf2 /mnt/c/Users/YourName/Desktop
Warning: Don't build in a shared folder (in /mnt/c). You'll probably have filename and line-ending problems.

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.

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.

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# You only need to do this once.
# Choose the appropriate drive letter.
sudo mkdir /mnt/d
# Now mount the drive.
sudo mount -t drvfs D: /mnt/d
# Now you can look at the contents, copy things, etc.
ls /mnt/d
cp firmware.bin /mnt/d
# etc.

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):

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.

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git clone
cd circuitpython
git submodule sync --quiet --recursive
git submodule update --init

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.

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make -C mpy-cross

Build CircuitPython

Now you're all set to build CircuitPython. If you're in the master 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/.

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cd ports/atmel-samd
make BOARD=circuitplayground_express

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

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cd ports/atmel-samd
make BOARD=circuitplayground_express TRANSLATION=es

Run your build!

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

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Create build-circuitplayground_express/firmware.bin
Create build-circuitplayground_express/firmware.uf2
python2 ../../tools/uf2/utils/ -b 0x2000 -c -o build-circuitplayground_express/firmware.uf2 build-circuitplayground_express/firmware.bin
Converting to uf2, output size: 485888, start address: 0x2000
Wrote 485888 bytes to build-circuitplayground_express/firmware.uf2.

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:

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# Double-click the reset button, then:
cp build-circuitplayground_express/firmware.uf2 /media/yourname/CPLAYBOOT

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.

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:

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make clean BOARD=...

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:

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git pull
git submodule sync
git submodule update --init
# Then make again.

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'll be writing all that up later.

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/

USB_VID = 0x239A
USB_PID = 0x8019
USB_PRODUCT = "CircuitPlayground Express"
USB_MANUFACTURER = "Adafruit Industries LLC"

CHIP_FAMILY = samd21


# Make room for frozen libs.


# Include these Python libraries in firmware.
FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_CircuitPlayground
FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_HID
FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_LIS3DH
FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_NeoPixel
FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_Thermistor

Notice the FROZEN_MPY_DIRS lines in the file. Pick the 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/

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FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_HID

Then add the library as a submodule:

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cd circuitpython/frozen
git submodule add
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.

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

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 ... /devices.h, along with the settings needed for each.

The chip(s) that are supported in a particular board are specified in the file for that board, in the line that defines EXTERNAL_FLASH_DEVICES. That's a comma-separated list, and EXTERNAL_FLASH_DEVICE_COUNT says how many are in the list. 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 chip data in devices.h takes significant space. We trim it down to include only those listed in EXTERNAL_FLASH_DEVICES for that board.

You can customize which USB devices to include in your CircuitPython build by adding some settings to the circuitpython/ports/port-choice/boards/board-choice/ file.

Customizing USB Devices

You can enable or disable the different available USB devices by using these flags and setting them to 1 or 0. You do not need to specify all these settings, only the ones that are different from the defaults for your build. 

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# Enable second CDC (serial) channel (usually on)
# Disable composite HID device (usually on)
# Disable MIDI (sometimes on)
# Disable mass storage (on by default)
# Enable WEBUSB (off by default)

Customizing USB HID Devices

Similarly, these flags control whether various USB HID devices are enabled or disabled. You only need to specify the ones that are different from the defaults for your build.

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# Disable Consumer Control (volume, etc.) (on by default)

# Enable digitizer tablet (off by default)

# Disable HID gamepad (usually on)

# Disable keyboard (always on)

# Disable mouse (always on)

# Enable SysControl (power, etc.) (off by default)

# Enable Microsoft XAC gamepad (off by default)

Side note: 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

Customizing USB Devices Before 6.2.0-beta.3

If you are changing a build before 6.2.0-beta.3 (actually before PR 4215), use this older way of specifying which USB devices to include. Add a line like one of these:

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# This is the default if USB_DEVICES is not specified.
# AUDIO refers to MIDI capability.

# Here's an example of providing only HID devices

# Provide only CDC and HID

Of course, if you disable MSC, you will not be able to load and edit programs via the CIRCUITPY drive. So get your program running with a regular CircuitPython build, and when you are satisfied, replace it with your custom build. If you need to edit the program again, reload the regular build.

Customizing HID Devices Before 6.2.0-beta.3

Similarly, you can specify which HID devices are available:

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# This is the default if USB_HID_DEVICES is not specified

# Provide only KEYBOARD and CONSUMER HID devices, for use as, say, a volume control.

The ports/esp32s2 build setup is a rather involved process. Please read the 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:

brew install cmake

On Linux you may need to install ninja and cmake:

sudo apt install ninja-build cmake


If you get an error while trying to make an esp32s2 board, check these possibilities:

  • Did you install the prerequisites, by running esp-idf/ You only need to do this once. Make sure python is pointing to python3 before you run esp-idf/
  • Did you run source esp-idf/ in the terminal window in which you are building? You need to do this in each fresh terminal window.

This guide was first published on Apr 26, 2018. It was last updated on Apr 26, 2018.