To init in boot mode:
	-Press S1 and S2
	-Release S1
	-Release S2

The device should resart in USB Bootloader


# windows
dfu-util.exe -a 0 -i 0 -s 0x08000000:leave -D  firmware.bin

# linux
dfu-util -a 0 -i 0 -s 0x08000000:leave -D firmware.bin