Creating modules

Modules in RIOT are well-defined units of code that provide a set of features to your application. This includes also drivers and to a certain extent ports for CPUs and boards (with some exceptions, see the porting guide for further information).

The general structure

Like applications, modules are directories containing source files and a Makefile. Additionally their API can be defined in one or more header files, residing in the include path of their super-module.

E.g. the Shell module is implemented in sys/shell and defines its API in sys/include/shell.h and the ISL29020 light sensor driver is implemented in drivers/isl29020 and defines its API in drivers/include/isl29020.h.

A module's Makefile just needs to include Makefile.base in the RIOT repository:

include $(RIOTBASE)/Makefile.base

If your module's name differs from the name of the directory it resides in you need to set the MODULE macro in addition.

When compiled a module always provides a MODULE_<MODULENAME> macro to the system. This way, other modules can check if the module is available in the current configuration or not.

Modules can be used by adding their name to the USEMODULE macro of your application's Makefile.

Pitfalls

The MODULE name should be unique or build breaks as modules overwrite the same output file.

This problem happened in the past for:

  • Packages root directory (libfixmath/u8g2)
  • boards/cpu/periph and their common boards/cpu/periph

Note: even if all boards and cpus implement the board and cpu modules, only one is used in an application so there is no conflict.

Module dependencies

Your module may depend on other modules to minimize code duplication. These dependencies are defined in Makefile.dep with the following syntax:

ifneq (,$(filter your_module,$(USEMODULE))) # if module in USEMODULE
USEMODULE += dep1 # add dependencies to USEMODULE
USEMODULE += dep2
endif

Note, that Makefile.dep is processed only once so you have to take care to add the dependency block for your module before your dependencies pull in their dependencies.

Modules outside of RIOTBASE

Modules can be defined outside RIOTBASE. In addition to add it to USEMODULE the user needs to add the module path to EXTERNAL_MODULE_DIRS.

The external module can optionally define the following files:

  • Makefile.include file to set global build configuration like CFLAGS or add API headers include paths to the USEMODULE_INCLUDES variable.
  • Makefile.dep file to set module dependencies

An example can be found in tests/external_module_dirs

Pseudomodules

Pseudomodules are modules that do not have any code. Their main use cases are to provide base information for dependencies to other modules or information to the code base via the MODULE_<MODULENAME> macro. Pseudomodules can provide header files too, if need be. To create a pseudomodule just add its name to the PSEUDOMODULES macro in Makefile.pseudomodules.