STM32H7 option byte programming

[Mvan .31]

Hi,

I'm trying to change the boot order of the STM32H745 to gate the M7 core and boot the M4 core.

This works fine in ST-Link utility ofcourse.

Now I'm trying this in code and this seems to not work.

I think the issue is with setting the bit from high to low.

FLASH_OBProgramInitTypeDef OBInit;
HAL_FLASHEx_OBGetConfig(&OBInit);
 
log_info("Usertype: %08x", OBInit.USERType);
 
if (OBInit.USERType & OB_USER_BCM7) {
	log_info("Changing option bytes");
	OBInit.USERType &= ~OB_USER_BCM7;
	if (HAL_FLASH_OB_Unlock() == HAL_OK)
		if (HAL_FLASH_Unlock() == HAL_OK)
			if (HAL_FLASHEx_OBProgram(&OBInit) == HAL_OK)
				if (HAL_FLASH_OB_Launch() == HAL_OK)
					if (HAL_FLASH_OB_Lock() == HAL_OK)
						if (HAL_FLASH_Lock() == HAL_OK)
						{
							log_info("Option bytes changed");
							log_info("Requires rebooting");
							//NVIC_SystemReset();
							return;
						}
	log_info("Failed changing option bytes");

All functions result in HAL_OK but the value doesn't change.

Am I missing something?

Melvin

[TDK · Accepted solution]

> OBInit.USERType &= ~OB_USER_BCM7;

I think you meant:

> OBInit.USERType = OB_USER_BCM7;

> OBInit.USERConfig = OB_BCM7_DISABLE;

What you posted makes no modification to BOOT_CM7.

Note that disabling the M7 core may make debugging harder, as it's the default access port for SWD.

edit: corrected a few typos

[Mvan .31]

Ah yes that solved the issue.

Now I understand the UserType/UserConfig thing.

Yes it seems it makes debugging unusable. I changed the access port to "3 - Cortex-M4" but it still won't connect in STM32CubeIDE.

ST-Link will happily connect though on port 3.