Embedded Flash memory (FLASH) RM0351
114/1830 DocID024597 Rev 5
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 will 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,
FLASH_PCROP1/2ER, FLASH_WRP1/2AR, FLASH_WRP1/2BR). These registers are
also used to modify options. If these registers are not modified by user, they reflects the
options states of the system. See Section : Modifying user options for more details.
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