macro has to be defined in configuration file.
+CONFIG_MODULE_CALLOUT
+ The 'callout' module is another timer manager that aims to replace the
+ scheduler module. The management of timers can be done either from an
+ asynchronous interruption or from the main program. This module is
+ able to handle priorities between timers and allow to reschedule
+ a timer later if its priority is too low.
+
+
CONFIG_TIME
This module can be used to get a human readable time. It uses the
scheduler module. Its goal is not to be very precise, but just