RM0440 Rev 4 117/2126
RM0440 Embedded Flash memory (FLASH) for category 3 devices
228
Modifying user options
The option bytes are programmed differently from a main memory user address. It is not
possible to modify independently user options of bank 1 or bank 2. The users Options of the
bank 1 are modified first.
To modify the user options value, follow the procedure below:
1. Check that no Flash memory operation is on going by checking the BSY bit in the Flash
status register (FLASH_SR).
2. Clear OPTLOCK option lock bit with the clearing sequence described above.
3. Write the desired options value in the options registers: Flash option register
(FLASH_OPTR), Flash PCROP1 Start address register (FLASH_PCROP1SR), Flash
PCROP1 End address register (FLASH_PCROP1ER), Flash WRP area A address
register (FLASH_WRP1AR), Flash WRP area B address register (FLASH_WRP1BR),
Flash PCROP2 Start address register (FLASH_PCROP2SR), Flash PCROP2 End
address register (FLASH_PCROP2ER), Flash Bank 2 WRP area A address register
(FLASH_WRP2AR), Flash Bank 2 WRP area B address register (FLASH_WRP2BR).
4. Set the Options Start bit OPTSTRT in the Flash control register (FLASH_CR).
5. Wait for the BSY bit to be cleared.
Note: Any modification of the value of one option is automatically performed by erasing both user
option bytes pages first (bank 1 and bank 2) and then programming all the option bytes with
the values contained in the flash option registers.
Option byte loading
After the BSY bit is cleared, all new options are updated into the Flash but they are not
applied to the system. They have effect on the system when they are loaded. Option bytes
loading (OBL) is performed in two cases:
– when OBL_LAUNCH bit is set in the Flash control register (FLASH_CR).
– after a power reset (BOR reset or exit from Standby/Shutdown modes).
Option byte loader performs a read of the options block and stores the data into internal
option registers. These internal registers configure the system and cannot be read with by
software. Setting OBL_LAUNCH generates a reset so the option byte loading is performed
under system reset.
Each option bit has also its complement in the same double word. During option loading, a
verification of the option bit and its complement allows to check the loading has correctly
taken place.
During option byte loading, the options are read by double word with ECC. If the word and
its complement are matching, the option word/byte is copied into the option register.
If the comparison between the word and its complement fails, a status bit OPTVERR is set.
Mismatch values are forced into the option registers:
– For USR OPT option, the value of mismatch is all options at ‘1’, except for
BOR_LEV which is “000” (lowest threshold)
– For WRP option, the value of mismatch is the default value “No protection”
– For RDP option, the value of mismatch is the default value “Level 1”
– For PCROP, the value of mismatch is “all memory protected”
On system reset rising, internal option registers are copied into option registers which can
be read and written by software (FLASH_OPTR, FLASH_PCROP1/2SR,
To Next Page
Loading...
Need help?
General
