STM32G474RE write to OPTR Register because BOOT0-Pin is floating

[ABach.4]

My hardware design doesn't connect the BOOT0-Pin to a specific voltage level. That's why I need to write to the OPTR Register so that the BOOT0-Pin is not read at the boot sequence.

I check the OPTR Register:

FLASH->OPTR = ffeff8aa
 RDP = aa
 BOR_LEV = 0
 nRST_STOP = 1
 nRST_STDBY = 1
 nRST_SHDW = 1
 IWDG_SW = 1
 IWDG_STOP = 1
 IWDG_STDBY = 1
 WWDG_SW = 1
 BFB2 = 0
 DBANK = 1
 nBOOT1 = 1
 SRAM_PE = 1
 CCMSRAM_RST = 1
 nSWBOOT0 = 1
 nBOOT0 = 1
 NRST_MODE = 3
 IRHEN = 1

I need to clear the nSWBOOT0 so that the BOOT0-pin is not been evaluated anymore.

I wrote a code sequence to clear the nSWBOOT0...

FLASH_OBProgramInitTypeDef FLASH_OBInitStruct;
 
HAL_FLASHEx_OBGetConfig(&FLASH_OBInitStruct);
 
FLASH_OBInitStruct.OptionType = OPTIONBYTE_USER;
FLASH_OBInitStruct.USERType = OB_USER_nSWBOOT0;
 
CLEAR_BIT(FLASH_OBInitStruct.USERConfig, FLASH_OPTR_nSWBOOT0);
 
printf("FLASH_OBProgramInitTypeDef\n");
printf(" OptionType = %" PRIx32 "\n", FLASH_OBInitStruct.OptionType);
printf(" RDPLevel = %" PRIx32 "\n", FLASH_OBInitStruct.RDPLevel);
printf(" USERType = %" PRIx32 "\n", FLASH_OBInitStruct.USERType);
printf(" USERConfig = %" PRIx32 "\n", FLASH_OBInitStruct.USERConfig);
printf(" PCROPConfig = %" PRIx32 "\n", FLASH_OBInitStruct.PCROPConfig);
printf("\n");
 
/* Unlock the option bytes block access */
HAL_FLASH_OB_Unlock();
 
HAL_FLASHEx_OBProgram(&FLASH_OBInitStruct);
 
/* Launch the option byte loading */
HAL_FLASH_OB_Launch();
 
/* Locks the option bytes block access */
HAL_FLASH_OB_Lock();

... that outputs the right value...

FLASH_OBProgramInitTypeDef
 OptionType = 4
 RDPLevel = aa
 USERType = 2000
 USERConfig = fbeff800
 PCROPConfig = 0

... but it goes to the HardFault_Handler:

My question: why?

[ABach.4]

I found something related here: Unlock readout protection

It first unlocks the Flash itself with HAL_FLASH_Unlock()

Now it works!

Here is the almost working example (it writes to OPTR Register but also reloads the program somehow):

FLASH_OBProgramInitTypeDef FLASH_OBInitStruct;
 
HAL_FLASHEx_OBGetConfig(&FLASH_OBInitStruct);
 
FLASH_OBInitStruct.OptionType = OPTIONBYTE_USER;
FLASH_OBInitStruct.USERType = OB_USER_nSWBOOT0;
 
CLEAR_BIT(FLASH_OBInitStruct.USERConfig, FLASH_OPTR_nSWBOOT0);
 
printf("FLASH_OBProgramInitTypeDef\n");
printf(" OptionType = %" PRIx32 "\n", FLASH_OBInitStruct.OptionType);
printf(" RDPLevel = %" PRIx32 "\n", FLASH_OBInitStruct.RDPLevel);
printf(" USERType = %" PRIx32 "\n", FLASH_OBInitStruct.USERType);
printf(" USERConfig = %" PRIx32 "\n", FLASH_OBInitStruct.USERConfig);
printf(" PCROPConfig = %" PRIx32 "\n", FLASH_OBInitStruct.PCROPConfig);
printf("\n");
 
/* Unlock the FLASH control register access */
HAL_FLASH_Unlock();
 
/* Unlock the option bytes block access */
HAL_FLASH_OB_Unlock();
 
HAL_FLASHEx_OBProgram(&FLASH_OBInitStruct);
 
/* Launch the option byte loading */
HAL_FLASH_OB_Launch();
 
/* Locks the option bytes block access */
HAL_FLASH_OB_Lock();
 
/* Lock the FLASH control register access */
HAL_FLASH_Lock();

Here is an other example from ST itself:

C:\Users\andreas\STM32Cube\Repository\STM32Cube_FW_G4_V1.4.0\Projects\NUCLEO-G474RE\Examples\FLASH\FLASH_WriteProtection\Src

For me the problem is solved!