Setting RDP option byte in STM32L452

[SLevi.1]

I have a problem programmatically setting RDP to level 1.

My code is:

OBInit.RDPLevel = OB_RDP_LEVEL_1;
OBInit.OptionType = OPTIONBYTE_RDP;
ret = HAL_FLASH_Unlock();
ret = HAL_FLASH_OB_Unlock();
/* Clear SR register */
CLEAR_BIT(FLASH->SR, FLASH_SR_BSY);
ret = HAL_FLASHEx_OBProgram(&OBInit);
ret = HAL_FLASH_OB_Lock();
ret = HAL_FLASH_Lock();
HAL_Delay(2000);
ret = HAL_FLASH_OB_Launch();
// shouldn't get to this point, as processor will reset

I had to put in the clear pf FLASH->SR, otherwise the "FLASH_WaitForLastOperation" would fail inside "FLASH_OB_RDPConfig". I've no idea why the flash should be busy at this stage.

Whether or not I run this under the debugger, the RDP byte never changes. The last HAL_Delay is to give the flash chance to be written properly before the launch resets the processor.

[TDK · Accepted solution]

The BSY bit is read-only. Wait for BSY to be low, you can't set it to a value.

You must call HAL_FLASH_OB_Launch before locking option bytes. Locking them prevents access.

Several examples out there for this. Here is one:

https://github.com/STMicroelectronics/STM32CubeL4/blob/93f2cde30d17996651d7b31f7091ab3dfe2f99bb/Projects/NUCLEO-L4R5ZI/Examples/FLASH/FLASH_WriteProtection/Src/main.c#L299

[Pierre_Paris]

Hello @SLevi.1, and @TDK,

I add this article named How to program STM32 Option Bytes with the HAL API.

Enjoy your reading ! :)

Pierre