265 lines
9.8 KiB
ReStructuredText
265 lines
9.8 KiB
ReStructuredText
.. _cmodules:
|
|
|
|
MicroPython external C modules
|
|
==============================
|
|
|
|
When developing modules for use with MicroPython you may find you run into
|
|
limitations with the Python environment, often due to an inability to access
|
|
certain hardware resources or Python speed limitations.
|
|
|
|
If your limitations can't be resolved with suggestions in :ref:`speed_python`,
|
|
writing some or all of your module in C (and/or C++ if implemented for your port)
|
|
is a viable option.
|
|
|
|
If your module is designed to access or work with commonly available
|
|
hardware or libraries please consider implementing it inside the MicroPython
|
|
source tree alongside similar modules and submitting it as a pull request.
|
|
If however you're targeting obscure or proprietary systems it may make
|
|
more sense to keep this external to the main MicroPython repository.
|
|
|
|
This chapter describes how to compile such external modules into the
|
|
MicroPython executable or firmware image. Both Make and CMake build
|
|
tools are supported, and when writing an external module it's a good idea to
|
|
add the build files for both of these tools so the module can be used on all
|
|
ports. But when compiling a particular port you will only need to use one
|
|
method of building, either Make or CMake.
|
|
|
|
An alternative approach is to use :ref:`natmod` which allows writing custom C
|
|
code that is placed in a .mpy file, which can be imported dynamically in to
|
|
a running MicroPython system without the need to recompile the main firmware.
|
|
|
|
|
|
Structure of an external C module
|
|
---------------------------------
|
|
|
|
A MicroPython user C module is a directory with the following files:
|
|
|
|
* ``*.c`` / ``*.cpp`` / ``*.h`` source code files for your module.
|
|
|
|
These will typically include the low level functionality being implemented and
|
|
the MicroPython binding functions to expose the functions and module(s).
|
|
|
|
Currently the best reference for writing these functions/modules is
|
|
to find similar modules within the MicroPython tree and use them as examples.
|
|
|
|
* ``micropython.mk`` contains the Makefile fragment for this module.
|
|
|
|
``$(USERMOD_DIR)`` is available in ``micropython.mk`` as the path to your
|
|
module directory. As it's redefined for each c module, is should be expanded
|
|
in your ``micropython.mk`` to a local make variable,
|
|
eg ``EXAMPLE_MOD_DIR := $(USERMOD_DIR)``
|
|
|
|
Your ``micropython.mk`` must add your modules source files relative to your
|
|
expanded copy of ``$(USERMOD_DIR)`` to ``SRC_USERMOD``, eg
|
|
``SRC_USERMOD += $(EXAMPLE_MOD_DIR)/example.c``
|
|
|
|
If you have custom compiler options (like ``-I`` to add directories to search
|
|
for header files), these should be added to ``CFLAGS_USERMOD`` for C code
|
|
and to ``CXXFLAGS_USERMOD`` for C++ code.
|
|
|
|
* ``micropython.cmake`` contains the CMake configuration for this module.
|
|
|
|
In ``micropython.cmake``, you may use ``${CMAKE_CURRENT_LIST_DIR}`` as the path to
|
|
the current module.
|
|
|
|
Your ``micropython.cmake`` should define an ``INTERFACE`` library and associate
|
|
your source files, compile definitions and include directories with it.
|
|
The library should then be linked to the ``usermod`` target.
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(usermod_cexample INTERFACE)
|
|
|
|
target_sources(usermod_cexample INTERFACE
|
|
${CMAKE_CURRENT_LIST_DIR}/examplemodule.c
|
|
)
|
|
|
|
target_include_directories(usermod_cexample INTERFACE
|
|
${CMAKE_CURRENT_LIST_DIR}
|
|
)
|
|
|
|
target_link_libraries(usermod INTERFACE usermod_cexample)
|
|
|
|
|
|
See below for full usage example.
|
|
|
|
|
|
Basic example
|
|
-------------
|
|
|
|
This simple module named ``cexample`` provides a single function
|
|
``cexample.add_ints(a, b)`` which adds the two integer args together and returns
|
|
the result. It can be found in the MicroPython source tree
|
|
`in the examples directory <https://github.com/micropython/micropython/tree/master/examples/usercmodule/cexample>`_
|
|
and has a source file and a Makefile fragment with content as descibed above::
|
|
|
|
micropython/
|
|
└──examples/
|
|
└──usercmodule/
|
|
└──cexample/
|
|
├── examplemodule.c
|
|
├── micropython.mk
|
|
└── micropython.cmake
|
|
|
|
|
|
Refer to the comments in these files for additional explanation.
|
|
Next to the ``cexample`` module there's also ``cppexample`` which
|
|
works in the same way but shows one way of mixing C and C++ code
|
|
in MicroPython.
|
|
|
|
|
|
Compiling the cmodule into MicroPython
|
|
--------------------------------------
|
|
|
|
To build such a module, compile MicroPython (see `getting started
|
|
<https://github.com/micropython/micropython/wiki/Getting-Started>`_),
|
|
applying 2 modifications:
|
|
|
|
1. Set the build-time flag ``USER_C_MODULES`` to point to the modules
|
|
you want to include. For ports that use Make this variable should be a
|
|
directory which is searched automatically for modules. For ports that
|
|
use CMake this variable should be a file which includes the modules to
|
|
build. See below for details.
|
|
|
|
2. Enable the modules by setting the corresponding C preprocessor macro to
|
|
1. This is only needed if the modules you are building are not
|
|
automatically enabled.
|
|
|
|
For building the example modules which come with MicroPython,
|
|
set ``USER_C_MODULES`` to the ``examples/usercmodule`` directory for Make,
|
|
or to ``examples/usercmodule/micropython.cmake`` for CMake.
|
|
|
|
For example, here's how the to build the unix port with the example modules:
|
|
|
|
.. code-block:: bash
|
|
|
|
cd micropython/ports/unix
|
|
make USER_C_MODULES=../../examples/usercmodule
|
|
|
|
You may need to run ``make clean`` once at the start when including new
|
|
user modules in the build. The build output will show the modules found::
|
|
|
|
...
|
|
Including User C Module from ../../examples/usercmodule/cexample
|
|
Including User C Module from ../../examples/usercmodule/cppexample
|
|
...
|
|
|
|
For a CMake-based port such as rp2, this will look a little different (note
|
|
that CMake is actually invoked by ``make``):
|
|
|
|
.. code-block:: bash
|
|
|
|
cd micropython/ports/rp2
|
|
make USER_C_MODULES=../../examples/usercmodule/micropython.cmake
|
|
|
|
Again, you may need to run ``make clean`` first for CMake to pick up the
|
|
user modules. The CMake build output lists the modules by name::
|
|
|
|
...
|
|
Including User C Module(s) from ../../examples/usercmodule/micropython.cmake
|
|
Found User C Module(s): usermod_cexample, usermod_cppexample
|
|
...
|
|
|
|
The contents of the top-level ``micropython.cmake`` can be used to control which
|
|
modules are enabled.
|
|
|
|
For your own projects it's more convenient to keep custom code out of the main
|
|
MicroPython source tree, so a typical project directory structure will look
|
|
like this::
|
|
|
|
my_project/
|
|
├── modules/
|
|
│ ├── example1/
|
|
│ │ ├── example1.c
|
|
│ │ ├── micropython.mk
|
|
│ │ └── micropython.cmake
|
|
│ ├── example2/
|
|
│ │ ├── example2.c
|
|
│ │ ├── micropython.mk
|
|
│ │ └── micropython.cmake
|
|
│ └── micropython.cmake
|
|
└── micropython/
|
|
├──ports/
|
|
... ├──stm32/
|
|
...
|
|
|
|
When building with Make set ``USER_C_MODULES`` to the ``my_project/modules``
|
|
directory. For example, building the stm32 port:
|
|
|
|
.. code-block:: bash
|
|
|
|
cd my_project/micropython/ports/stm32
|
|
make USER_C_MODULES=../../../modules
|
|
|
|
When building with CMake the top level ``micropython.cmake`` -- found directly
|
|
in the ``my_project/modules`` directory -- should ``include`` all of the modules
|
|
you want to have available:
|
|
|
|
.. code-block:: cmake
|
|
|
|
include(${CMAKE_CURRENT_LIST_DIR}/example1/micropython.cmake)
|
|
include(${CMAKE_CURRENT_LIST_DIR}/example2/micropython.cmake)
|
|
|
|
Then build with:
|
|
|
|
.. code-block:: bash
|
|
|
|
cd my_project/micropython/ports/esp32
|
|
make USER_C_MODULES=../../../../modules/micropython.cmake
|
|
|
|
Note that the esp32 port needs the extra ``..`` for relative paths due to the
|
|
location of its main ``CMakeLists.txt`` file. You can also specify absolute
|
|
paths to ``USER_C_MODULES``.
|
|
|
|
All modules specified by the ``USER_C_MODULES`` variable (either found in this
|
|
directory when using Make, or added via ``include`` when using CMake) will be
|
|
compiled, but only those which are enabled will be available for importing.
|
|
User modules are usually enabled by default (this is decided by the developer
|
|
of the module), in which case there is nothing more to do than set ``USER_C_MODULES``
|
|
as described above.
|
|
|
|
If a module is not enabled by default then the corresponding C preprocessor macro
|
|
must be enabled. This macro name can be found by searching for the ``MP_REGISTER_MODULE``
|
|
line in the module's source code (it usually appears at the end of the main source file).
|
|
The third argument to ``MP_REGISTER_MODULE`` is the macro name, and this must be set
|
|
to 1 using ``CFLAGS_EXTRA`` to make the module available. If the third argument is just
|
|
the number 1 then the module is enabled by default.
|
|
|
|
For example, the ``examples/usercmodule/cexample`` module is enabled by default so
|
|
has the following line in its source code:
|
|
|
|
.. code-block:: c
|
|
|
|
MP_REGISTER_MODULE(MP_QSTR_cexample, example_user_cmodule, 1);
|
|
|
|
Alternatively, to make this module disabled by default but selectable through
|
|
a preprocessor configuration option, it would be:
|
|
|
|
.. code-block:: c
|
|
|
|
MP_REGISTER_MODULE(MP_QSTR_cexample, example_user_cmodule, MODULE_CEXAMPLE_ENABLED);
|
|
|
|
In this case the module is enabled by adding ``CFLAGS_EXTRA=-DMODULE_CEXAMPLE_ENABLED=1``
|
|
to the ``make`` command, or editing ``mpconfigport.h`` or ``mpconfigboard.h`` to add
|
|
|
|
.. code-block:: c
|
|
|
|
#define MODULE_CEXAMPLE_ENABLED (1)
|
|
|
|
Note that the exact method depends on the port as they have different
|
|
structures. If not done correctly it will compile but importing will
|
|
fail to find the module.
|
|
|
|
|
|
Module usage in MicroPython
|
|
---------------------------
|
|
|
|
Once built into your copy of MicroPython, the module
|
|
can now be accessed in Python just like any other builtin module, e.g.
|
|
|
|
.. code-block:: python
|
|
|
|
import cexample
|
|
print(cexample.add_ints(1, 3))
|
|
# should display 4
|