The micropython code base

Since we are going to test our code mainly on the unix port, we set that as the current working directory.

!cd ../../micropython/ports/unix/

/home/v923z/sandbox/micropython/v1.11/micropython/ports/unix

The micropython codebase itself is set up a rather modular way. Provided you cloned the micropython repository with

!git clone https://github.com/micropython/micropython.git

onto your computer, and you look at the top-level directories, you will see something like this:

!ls ../../../micropython/

ACKNOWLEDGEMENTS    docs      lib    pic16bit   teensy   zephyr
bare-arm        drivers   LICENSE    py         tests
cc3200                  esp8266   logo       qemu-arm   tools
CODECONVENTIONS.md  examples  minimal        README.md  unix
CONTRIBUTING.md     extmod    mpy-cross  stmhal     windows

Out of all the directoties, at least two are of particular interest. Namely, /py/, where the python interpreter is implemented, and /ports/, which contains the hardware-specific files. All questions pertaining to programming micropython in C can be answered by browsing these two directories, and perusing the relevant files therein.

User modules in micropython

Beginning with the 1.10 version of micropython, it became quite simple to add a user-defined C module to the firmware. You simply drop two or three files in an arbitrary directory, and pass two compiler flags to make like so:

!make USER_C_MODULES=../../../user_modules CFLAGS_EXTRA=-DMODULE_EXAMPLE_ENABLED=1 all

Here, the USER_C_MODULES variable is the location (relative to the location of make) of your files, while CFLAGS_EXTRA defines the flag for your particular module. This is relevant, if you have many modules, but you want to include only some of them.

Alternatively, you can set the module flags in mpconfigport.h (to be found in the port’s root folder, for which you are compiling) as

#define MODULE_SIMPLEFUNCTION_ENABLED (1)
#define MODULE_SIMPLECLASS_ENABLED (1)
#define MODULE_SPECIALCLASS_ENABLED (1)
#define MODULE_KEYWORDFUNCTION_ENABLED (1)
#define MODULE_CONSUMEITERABLE_ENABLED (1)
#define MODULE_VECTOR_ENABLED (1)
#define MODULE_RETURNITERABLE_ENABLED (1)
#define MODULE_PROFILING_ENABLED (1)
#define MODULE_MAKEITERABLE_ENABLED (1)
#define MODULE_SUBSCRIPTITERABLE_ENABLED (1)
#define MODULE_SLICEITERABLE_ENABLED (1)
#define MODULE_VARARG_ENABLED (1)
#define MODULE_STRINGARG_ENABLED (1)

and then call make without the CFLAGS_EXTRA flag:

!make USER_C_MODULES=../../../user_modules all

This separation of the user code from the micropython code base is definitely a convenience, because it is much easier to keep track of changes, and also because you can’t possibly screw up micropython itself: you can also go back to a working piece of firmware by dropping the USER_C_MODULES argument of make.