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A module and utility to flash Python onto the BBC micro:bit.

Project description



A utility for flashing the BBC micro:bit with Python scripts and the MicroPython runtime. You pronounce the name of this utility “micro-flash”. ;-)

It provides three services:

  1. A library of functions to programatically create a hex file and flash it onto a BBC micro:bit.

  2. A command line utility called uflash that will flash Python scripts onto a BBC micro:bit.

  3. A command line utility called py2hex for creating hex files from Python scripts and saving them on the local filesystem

Several essential operations are implemented:

  • Encode Python into the hex format.

  • Embed the resulting hexified Python into the MicroPython runtime hex.

  • Extract an encoded Python script from a MicroPython hex file.

  • Discover the connected micro:bit.

  • Copy the resulting hex onto the micro:bit, thus flashing the device.

  • Specify the MicroPython runtime hex in which to embed your Python code.


To install simply type:

$ pip install uflash

…and the package will download from PyPI. If you wish to upgrade to the latest version, use the following command:

$ pip install --no-cache --upgrade uflash

NB: You must use a USB data cable to connect the micro:bit to your computer (some cables are power only). You’re in good shape if, when plugged in, the micro:bit appears as a USB storage device on your file system.

Linux users: For uflash to work you must ensure the micro:bit is mounted as a USB storage device. Usually this is done automatically. If not you’ve probably configured automounting to be off. If that’s the case, we assume you have the technical knowledge to mount the device yourself or to install the required kernel modules if they’re missing. Default installs of popular Linux distros “should just work” (tm) out of the box given a default install.

Command Usage


To read help simply type:

$ uflash --help


$ uflash -h

To discover the version information type:

$ uflash --version

If you type the command on its own then uflash will attempt to find a connected BBC micro:bit and flash an unmodified default version of the MicroPython runtime onto it:

$ uflash
Flashing Python to: /media/ntoll/MICROBIT/micropython.hex

To flash a version of the MicroPython runtime with a specified script embedded within it (so that script is run when the BBC micro:bit boots up) then pass the path to the Python script in as the first argument to the command:

$ uflash
Flashing to: /media/ntoll/MICROBIT/micropython.hex

You can let uflash watch for changes of your script. It will be flashed automatically every time you save it:

$ uflash -w


$ uflash --watch

At this point uflash will try to automatically detect the path to the device. However, if you have several devices plugged in and/or know what the path on the filesystem to the BBC micro:bit already is, you can specify this as a second argument to the command:

$ uflash /media/ntoll/MICROBIT
Flashing to: /media/ntoll/MICROBIT/micropython.hex

You can even flash multiple devices at once:

$ uflash /media/ntoll/MICROBIT /media/ntoll/MICROBIT1
Flashing to: /media/ntoll/MICROBIT/micropython.hex
Flashing to: /media/ntoll/MICROBIT1/micropython.hex

To extract a Python script from a hex file use the “-e” flag like this:

$ uflash -e something.hex

This will save the Python script recovered from “something.hex” into the file “”. If you don’t supply a target the recovered script will emit to stdout.

If you’re developing MicroPython and have a custom runtime hex file you can specify that uflash use it instead of the built-in version of MicroPython in the following way:

$ uflash -r firmware.hex


$ uflash --runtime=firmware.hex


To create output .hex files in the same directory as the input .py files:

$ py2hex tests/
Hexifying as: tests/example.hex

py2hex includes that same -r/–runtime and -m/–minify options as uflash and adds an additional option -o/–outdir:

To create output .hex files in a different directory:

$ py2hex -o /tmp
Hexifying as: /tmp/example.hex


$ py2hex --outdir /tmp
Hexifying as: /tmp/example.hex

py2hex can handle multiple input files:

$ py2hex
Hexifying as: a.hex
Hexifying as: b.hex
Hexifying as: c.hex


$ py2hex *.py
Hexifying as: a.hex
Hexifying as: b.hex
Hexifying as: c.hex


The source code is hosted in GitHub. Please feel free to fork the repository. Assuming you have Git installed you can download the code from the canonical repository with the following command:

$ git clone

Ensure you have the correct dependencies for development installed by creating a virtualenv and running:

$ pip install -r requirements.txt

To locally install your development version of the module into a virtualenv, run the following command:

$ python develop

There is a Makefile that helps with most of the common workflows associated with development. Typing make on its own will list the options thus:

$ make

There is no default Makefile target right now. Try:

make clean - reset the project and remove auto-generated assets.
make pyflakes - run the PyFlakes code checker.
make pep8 - run the PEP8 style checker.
make test - run the test suite.
make coverage - view a report on test coverage.
make check - run all the checkers and tests.
make package - create a deployable package for the project.
make rpm - create an rpm package for the project.
make publish - publish the project to PyPI.
make docs - run sphinx to create project documentation.

Release History


  • Updated to the latest version of MicroPython for micro:bit (1.0.1)

  • This is the version of uflash to be used in Mu 1.0.2.


  • Update to the latest version of MicroPython for micro:bit (1.0.0).

  • This is the version of uflash to be used in Mu 1.0.1.


  • Update to latest version of MicroPython for micro:bit (1.0.0-rc.3).


  • Update to latest version of MicroPython. Thanks to Damien George and Carlos Pereira Atencio for their hard work.

  • This is the version of uflash to be used in Mu 1.0.0 (final).


  • Update to latest version of MicroPython. Thanks to Damien George.

  • Add attribute called MICROPYTHON_VERSION to report the version of MicroPython bundled with uflash.


  • Update to the latest version of MicroPython for the BBC micro:bit – fixes a bug relating to flooding and the radio module. As always, many thanks to Damien George for his work on MicroPython.


  • Update to latest version of MicroPython for the BBC micro:bit (many thanks to Damien George for his amazing efforts!).

  • Add a –version flag to uflash that causes it to print the current version number (many thanks to Lenz Grimmer for this work).

  • Allow uflash to accept the content of a script as well as the path to a script (many thanks to Zander Brown for this work).

  • Ensure uflash works nicely / better with external tools (many thanks to Lex Robinson for this work).

  • Added copyright and license information to the start of the script.


  • Refactor hex extraction to not depend on extended address record before script (thanks Carlos).

  • Refactor tox tests to fix Windows related Gremlin (thanks again, Carlos).


  • Watch for changes in a script. Automatically flash on save.


  • Update runtime to include latest bug fixes and inclusion of input() builtin.

  • Detecting drives on Windows 10 no longer causes pop-ups in certain situations.

  • Documentation updates.


  • Add support for flash multiple microbits.


  • Update runtime to include audio and speech modules.


  • Update runtime to include the new radio module.


  • Update runtime to include file system related changes.

  • Runtime updated to version 1.0 of MicroPython for the BBC micro:bit.


  • Runtime update to fix display related bug.


  • Runtime update to latest version of the DAL (swaps pins 4 and 5).


  • Runtime update to fix error reporting bug.


  • Documentation update.

  • Help text update.


  • Add ability to specify a MicroPython runtime to use.

  • Test fixes.


  • Updated to latest version of MicroPython runtime.


  • Works with Python 2.7 (thanks to @Funkyhat).

  • Updated to the latest build of MicroPython for the BBC micro:bit.

  • Minor refactoring and updates to the test suite due to MicroPython updates.


  • Minor code refactor.

  • Documentation update.


  • Feature complete.

  • Comprehensive test suite - 100% coverage.

  • Tested on Linux and Windows.

  • Documentation.

  • Access via the “uflash” command.


  • Initial release. Basic functionality.

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