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.
git clone https://github.com/adafruit/circuitpython.git 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.
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/.
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.
cd ports/atmel-samd make BOARD=circuitplayground_express TRANSLATION=es
Create build-circuitplayground_express/firmware.bin Create build-circuitplayground_express/firmware.uf2 python2 ../../tools/uf2/utils/uf2conv.py -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:
# 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:
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:
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.
