Required dependencies of applications may change depending on the

target board or architecture. This is especially

relevant for networking applications where multiple hardware implementations

exist and the appropriate one has to be chosen for the given board

or architecture.

To achieve this task elegantly, a `Makefile.board.dep` file can be

created in the application folder, which is automatically included and

evaluated by RIOT build system during the dependency resolution phase.

This ensures that all the relevant variables such as `FEATURES_USED` or the

`USEMODULE` list are fully populated.

~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.mk}