Attach callbacks with the assignment operator rather than with the
deprecated attach function. This fixes deprecation warnings.
This patch also adds the ability to attach a Callback directly.
The local static initialization in USB was causing multiple problems:
-Configurable descriptor values are set only once
-USB descriptor initialization causes a trap in debug builds since
this is acquiring a mutex in an interrupt handler
-Extra ram used since all descriptors are in RAM
This patch fixes these problems by making fixed descriptors
static const so they are stored in flash and never need to be
initialized and by making descriptors that do change a member
of the class so they are always initialized when requested
rather than once though lazy static local initialization.
Russ Butler
Michel Jaouen
ccli8
Christopher Haster