Creating modules {#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 <!-- @ref porting-guide --> the porting guide for further information).

The general structure {#the-general-structure}

Like @ref creating-an-application "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 @ref sys_shell module is implemented in sys/shell and defines its API in sys/include/shell.h and the @ref drivers_isl29020 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.

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-outside-of-riotbase}

Modules can be defined outside RIOTBASE. In addition to add it to USEMODULE the user needs to add the path to the module to EXTERNAL_MODULES and add the include path to the API definitions to INCLUDES.

Pseudomodules {#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.