Creating-modules.md

+**Author** Zakaria Kasmi
+
+\[\[_TOC_\]\]
+
+Well-defined units of code in the RcdMathLib that provide a set of features are encapsulated in a
+module. RcdMathLib is module-based and composed of the following main modules:
+
+* Linear algebra module
+* Non-Linear algebra module
+* Localization module
+
+Each main module includes sub-modules, for more details see 
+@ref structure "The structure of the RcdMathLib".
+
+@note The following chapters concerning only resource-limited devices. 
+
+The general structure                                  {#the-general-structure}
+=====================
+Modules are directories containing source and header files as well as a Makefile.
+Furthermore, their API can be defined in one or more header files, residing in the include path of
+their super-module.
+
+For example, the matrix sub-module is implemented in the @ref basic_operations sub-module, in the 
+`linear_algebra/basic_operations` directory. Its API is defined in
+`linear_algebra/basic_operations/matrix.h`. 
+
+A module's Makefile just needs to include `Makefile.base` in the RIOT repository as well as 
+`Makefile.base` and `Makefile.include` in the RcdMathLib repository:
+
+~~~~~~~~~~~~~~~~~~~ {.mk}
+include $(RIOTBASE)/Makefile.base
+include $(RCDMATHLIB)/linear_algebra/matrix_decompositions/Makefile.include
+include $(RCDMATHLIB)/linear_algebra/matrix_decompositions/Makefile.dep 
+~~~~~~~~~~~~~~~~~~~
+
+The `Makefile.base` and `Makefile.include` macros in the example above are includes for 
+the linear algebra module.
+
+If your module's name differs from the name of the directory it resides in you
+need to set the `MODULE` macro in addition.
+
+The `Makefile.dep` serves to define dependencies and the `Makefile.include` to append target
+specific information to variables like INCLUDES. Modules can be used by adding their name to the
+`USEMODULE` macro of the application's Makefile.
+
+
+Module dependencies
+===================
+The module may depend on other modules to minimize code duplication. These
+dependencies are defined in `Makefile.dep` with the following syntax:
+
+~~~~~~~~~~~~~~~~~~~ {.mk}
+ifneq (,$(filter your_module,$(USEMODULE))) # if module in USEMODULE
+  USEMODULE += dep1                         # add dependencies to USEMODULE
+  USEMODULE += dep2
+endif
+~~~~~~~~~~~~~~~~~~~
+
+@note `Makefile.dep` is processed only once therefore, the dependency block for a module must be 
+added *before*  dependencies pull in their dependencies.
+