Added make rule to clear option bytes

Author: vedderb

Makefile

@@ -284,6 +284,9 @@ upload: build/$(PROJECT).bin
 #	openocd -f interface/stlink-v2.cfg -c "set WORKAREASIZE 0x2000" -f target/stm32f4x_stlink.cfg -c "program build/$(PROJECT).elf verify reset" # Older openocd
 	openocd -f board/stm32f4discovery.cfg -c "reset_config trst_only combined" -c "program build/$(PROJECT).elf verify reset exit" # For openocd 0.9
 
+clear_option_bytes:
+	openocd -f board/stm32f4discovery.cfg -c "init" -c "stm32f2x unlock 0" -c "mww 0x40023C08 0x08192A3B; mww 0x40023C08 0x4C5D6E7F; mww 0x40023C14 0x0fffaaed" -c "exit"
+
 #program with olimex arm-usb-tiny-h and jtag-swd adapter board. needs openocd>=0.9
 upload-olimex: build/$(PROJECT).bin
 	openocd -f interface/ftdi/olimex-arm-usb-tiny-h.cfg -f interface/ftdi/olimex-arm-jtag-swd.cfg -c "set WORKAREASIZE 0x2000" -f target/stm32f4x.cfg -c "program build/$(PROJECT).elf verify reset"