Sequence should be:
HAL_FLASH_Unlock();
HAL_FLASH_OB_Unlock();
HAL_FLASHEx_OBProgram(&ob_cfg);
HAL_FLASHEx_OB_Launch();
The last function causes a reset which makes the option bytes active. It doesn't matter what code you have after this because the mcu resets, but I would still monitor the return value.
The reference manual goes over the sequence needed to perform these steps. You can also look at the source to find out what HAL is doing. For example:
/**
* @brief Launch the option byte loading.
* @retval HAL Status
*/
HAL_StatusTypeDef HAL_FLASH_OB_Launch(void)
{
/* Set the bit to force the option byte reloading */
SET_BIT(FLASH->CR, FLASH_CR_OBL_LAUNCH);
/* We should not reach here : Option byte launch generates Option byte reset
so return error */
return HAL_ERROR;
}
It makes sense that this returns HAL_ERROR. The first statement, which would normally reset the chip, doesn't work because the option bytes are locked.
If you find checking for return values a pain, consider defining a macro:
#define RUN_HAL(x) if ((x) != HAL_OK) {while (1);}
...
RUN_HAL(HAL_FLASH_Unlock());
At least that way you have a chance of catching errors when they happen, instead of having to hunt them down afterwards.
If you feel a post has answered your question, please click "Accept as Solution".
