Note: Once any quantity of data is reported by
the USBUSARTRxGetLength routine, the
CDC serial driver will not accept additional
data from the host until the USBUSARTRx
routine is called again.
Since this simple application is only
designed to be “half duplex”, either transmitting
or receiving (but, not both at the
same time), it will not call USBUSARTRx
again immediately. A more advanced
application could do so using a different
buffer, allowing the system to appear to
receive data at the same time it was transmitting
data, providing “[B]full-duplex”[/B]
functionality