This provides the correct binary semaphore behaviour that was expected
by the equeue layer, removes concerns around semaphore overflow, and
reduces the number of spurious wakeups which may save a bit of power.
This also fixes some issues we were seeing around the RTX 5 changes
to semaphore behaviour.
Before, if the semaphore recieved a wait of zero, the semaphore
would erronously drop the ticker event to wake up the device,
causing the device to go to sleep without any mechanism to wake
itself up.
During a dispatch operation, the event queue dispatches all events
that have expired, so the call to equeue_sema_wait very rarely
has a wait of zero. But this can happen when an event is posted
just after a dispatch has occured.
Added mbed-events from https://github.com/ARMMbed/mbed-events. Changes
from upstream:
- the whole code is licensed under the Apache license. Sources and
headers were updates with this information.
- removed the porting layers for Windows and FreeRTOS and the references
to these porting layers in equeue_platform.h.
- moved the TESTS directory in mbed-events to the TESTS directory of
mbed-os.