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ARM: trigger STM32 Option Byte Loading after Flash Download

Information in this knowledgebase article applies to:

  • STM32 devices supporting the OBL_LAUNCH bit


I use the MDK to program the option bytes of ST devices. Unfortunately I have found that changes in the option bytes need a full power-on reset cycle after flashing to get active. Is there a way, to activate the new options bytes automatically without the need to do a manual power cycle of the device?


For some STM32 device families it is possible to start the option byte loading by setting the OBL_LAUNCH bit.
If your device supports this, and the provisions for this are implemented in the Device Family Pack version you have installed, you find in the dbgconf file a Flash Download Options -> Option Byte Loading checkbox. It is off by default. After enabling it and saving the dbgconf file, after the next Flash Download, the Option Byte Loading is started by setting the OBL_LAUNCH bit. This method also causes an additional reset.


Last Reviewed: Friday, January 10, 2020

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