ST STM32L0x3 User Manual

Flash program memory and data EEPROM (FLASH) RM0367
122/1043 RM0367 Rev 7
3.8.2 Mismatch when loading protection flags
When there is a mismatch during an Option byte loading, the memory interface sets the
default value in registers.
In the Option byte area, there are three kinds of protection information:
• RDPROT
This configuration sets the Protection Level. As explained in the next section, changing
this level changes the possibility to access the NVM and the product. The default value
is Level 1. It is possible to return to Level 0 from Level 1 but all content of the data
EEPROM and Flash program memory will be deleted (mass erase). It is always
possible to move to Level 2, but not to change protection levels when Level 2 is loaded
(if the user writes in Option bytes a Level 2 but never reloads the Option bytes, the
memory interface continues to works in the previous level and it is possible to write
again a different protection level in the Option bytes area).
• WPRMOD
This flag is independent from RDPROT and set if the Flash program memory is
protected from read or write. When this flag is 1 (read protection), the only way to reset
it is to request a mass erase (also returning to Level 0). This means that there is no
way to remove the read protection when the device is in Level 2. The default value is 1
(read protection) and a mismatch on this bit also generates the default value for the
WRPROT configuration.
• WRPROT
This configuration sets which sectors of the Flash program memory are read- or write-
protected. If the read protection is disabled (WPRMOD = 0), 1 must be set in the right
bit to protect a sector. If the read protection is enabled (WPRMOD = 1), 0 must be in
the right bit to protect a sector. If during boot there is a mismatch on WPRMOD, this
configuration is loaded with zeros so that all sectors of the Flash program memory are
protected from read. If WPRMOD has been read correctly but there is a mismatch
reading WRPROT, the register will be loaded with zeros if WPRMOD = 1, and with
ones if WPRMOD = 0.
Thus, a mismatch on a protection can have a serious impact on the normal execution of
code (if it is in the Flash program memory): when there is a read protection, only a fetch is
possible. In the Flash program memory, some values are read as data (the constants, for
example) during a code execution; protecting all sectors from read prevents the execution of
the application code from the Flash program memory.
3.8.3 Reloading Option bytes by software
It is possible to request an Option byte reloading by setting the OBL_LAUNCH flag to 1 in
the FLASH_PECR register. This bit can be set only when OPTLOCK = 0 (and PELOCK =
0). Setting this bit, the ongoing write/erase is completed, but no new write/erase or read
operation is executed.
The reload of Option bytes generates a reset of the device but without a power-down. The
options must be reloaded after every change of the Option bytes in the NVM, so that the
changes can apply. It is possible to reload by setting OBL_LAUNCH, or with a power-on of
the V18 domain (i.e. after a power-on reset or after a standby).

ST STM32L0x3 Specifications

General

Brand	ST
Model	STM32L0x3
Category	Microcontrollers
Language	English