You may define some flags to be passed to tasks at compile time.
They will be added to compile line as `-DKEY=value` on every source file for a given task

== Warning ==

Defined values when compiling a C file are unpredictable if
 * This C file is '''shared between tasks'''
 * The task corresponding to the C-file is '''instanciated more than once''' with '''different''' defines

If the only purpose is to pass up a numeric value, you should use `consts`.