Remove readout protection via USB without system reset on STM32F205

[jeffy]

 

Hi,

I need to downgrade the RDP level from Level 1 to Level 0 on an STM32F205 without triggering an automatic system reset, as I do not have access to the BOOT0 pin.

My workflow is as follows: I write the firmware to the device and then set the RDP level to 1. This works as expected. However, when I want to write new firmware to the device, I first need to reset the RDP level back to 0. This automatically triggers a system reset, which makes access to the BOOT0 pin necessary.

I have written my own frontend for the STM32CubeProgrammer API, but I have not been able to directly write to the option byte registers.

Is what I am trying to achieve possible, or is the automatic reset unavoidable when downgrading RDP from Level 1 to Level 0?

Thank you.

[FBL]

Hi ​@jeffy 

On STM32F205, this can be done from the system bootloader or through SWD/JTAG because option bytes are still configurable at Level 1. But this causes a mass erase of Flash memory and backup SRAM. So, the reset cannot be avoided.

[jeffy]

Hello FBL,

 

Thank you for your reply.

 

I just want to make sure that we are referring to the same thing. By “reset”, I mean the microcontroller rebooting.

 

If we are talking about the same behavior, I do not understand why the device has to leave DFU mode when erasing the Flash memory and backup SRAM. Do you know of any application note or documentation that describes this behavior?

 

Best regards,

[FBL]

Hi ​@jeffy 
You can refer to this article How to change the Read Out protection on STM32F2 | Community

Clearly states only option bytes will not be erased in this process.