To improve stability if the sketch overwrite the last SRAM location
(in this case the double tap doesn't work but at least the sketch
starts without problems)

Bootloader is activated by quickly double tapping to the reset button

Fixed NMI handling.

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

For some reason the blocking read from the original USB-CDC driver
is not reliable. As a workaround it has been reimplemented using a
polling loop with the non-blocking read function that, instead, is
much more reliable.

Eventually the USB_Read_blocking(..) in cdc_enumerate.c will be fixed
in the future.

Interrupt based implementation that works on every pin.

- Renamed Tone.cpp.disabled to Tone.cpp
- Removed commented legacy AVR code from Tone.cpp

This reverts commit bc7115b104428f9bea4fdfa1b6af245085f6f542.

This reverts commit 5024bce531bfeb6f70844f76ea09d7e7de31a067.

Conflicts:
	hardware/arduino/sam/platform.txt