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).
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
A module's Makefile just needs to include
Makefile.base in the RIOT repository:
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 name should be unique or build breaks as modules overwrite the same output file. This might for example lead to
undefined reference to errors in the linker which can be hard to track down.
This problem happened in the past for:
Note: even if all boards and cpus implement the
cpu modules, only one is used in an application so there is no conflict.
Your module may depend on other modules to minimize code duplication. These dependencies are defined in
Makefile.dep with the following syntax:
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 can be defined outside
RIOTBASE. In addition to add it to
USEMODULE the user needs to add the directory (or directories) containing external modules to
External modules can optionally define the following files:
Makefile.include file to set global build configuration like
CFLAGS or add API headers include paths to the
Makefile.dep file to set module dependencies
NOTE: The name of an external module must be unique (both in regard to other external modules, as well to native RIOT modules). Additionally, the directory containing the module must match the module name, e.g. module
foo must be located in
An example can be found in
Pseudomodules are modules that are not static libraries, i.e. do not generate a
<module name>.a file.
To create a pseudomodule just add its name to
PSEUDOMODULES += <modulename> in alphabetical order.
A Pseudomodule may or may not have a source file associated with it. To make the distinction between them we will refer to those that don't as true-Pseudomodules.
The main use case for true-Pseudomodules is to provide base information for dependencies to other modules or information to the code base via the
Pseudomodules with source code exist under a "real"
MODULE since they will generate a
<pseudomodule_name>.o file grouped under that
These modules appear in RIOT under two forms:
Conditionally included source files:
foo/Makefile you add the source file to the
SRC variable, conditioned on the Pseudomodule inclusion
sys/net/ble/skald for an example in code.
SUBMODULES in a
SRC file excluded from
foo/Makefile will be considered
SUBMODULES. In the example above
eggs.c. These source files will be conditionally included depending if the modules have been added, i.e.
USEMODULE += foo_ham foo_eggs (it's the same as case 1 but handled automatically in
SUBMODULES mechanism is more flexible since
BASE_MODULE allows matching the only parts of compounded module names and only match against part of that name.
sys/ztimer/Makefile for an example in code.
SUBMODULES can also be true-pseudomodules, or become one by conditionally excluding the source files by adding them to
To help you start writing a module, the RIOT build system provides the
generate-module make target. It is a wrapper around the riotgen command line tool that is helpful when starting to implement a module: all required files are generated with copyright headers, doxygen groups, etc, so you can concentrate on the module implementation. The module source files are created in the
From the RIOT base directory, run:
Then answer a few questions about the driver:
Other global information (author name, email, organization) should be retrieved automatically from your git configuration.
Once completed, the module files are located in
sys/<module name>/<module name>.c and