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RM0351 Embedded Flash memory (FLASH)
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3.5.2 Proprietary code readout protection (PCROP)
Apart of the flash memory can be protected against read and write from third parties. The
protected area is execute-only: it can only be reached by the STM32 CPU, as an instruction
code, while all other accesses (DMA, debug and CPU data read, write and erase) are
strictly prohibited. One area per bank can be selected, with double word (64-bit) granularity.
An additional option bit (PCROP_RDP) allows to select if the PCROP area is erased or not
when the RDP protection is changed from Level 1 to Level 0 (refer to Changing the Read
protection level).
Each PCROP area is defined by a start page offset and an end page offset related to the
physical Flash bank base address. These offsets are defined in the PCROP address
registers Flash Bank 1 PCROP Start address register (FLASH_PCROP1SR), Flash Bank 1
PCROP End address register (FLASH_PCROP1ER), Flash Bank 2 PCROP Start address
register (FLASH_PCROP2SR), Flash Bank 2 PCROP End address register
(FLASH_PCROP2ER).
The Bank “x” PCROP (x=1,2) area is defined from the address: Bank “x” Base address +
[PCROPx_STRT x 0x8] (included) to the address: Bank “x” Base address +
[(PCROPx_END+1) x 0x8] (excluded). The minimum PCROP area size is two double-words
(128 bits).
For example, to protect by PCROP from the address 0x08062F80 (included) to the address
0x08070004 (included):
• if boot in flash is done in Bank 1, FLASH_PCROP1SR and FLASH_PCROP1ER
registers must be programmed with:
– PCROP1_STRT = 0xC5F0.
– PCROP1_END = 0xE000.
• If the two banks are swapped, the protection must apply to bank 2, and
FLASH_PCROP2SR and FLASH_PCROP2ER register must be programmed with:
– PCROP2_STRT = 0xC5F0.
– PCROP2_END = 0xE000.
Any read access performed through the D-bus to a PCROP protected area will trigger
RDERR flag error.
Any PCROP protected address is also write protected and any write access to one of these
addresses will trigger WRPERR.
Any PCROP area is also erase protected. Consequently, any erase to a page in this zone is
impossible (including the page containing the start address and the end address of this
zone). Moreover, a software mass erase cannot be performed if one zone is PCROP
protected.
For previous example, due to erase by page, all pages from page 0xC5 to 0xE0 are
protected in case of page erase. (All addresses from 0x08062800 to 0x080707FF can’t be
erased).
Deactivation of PCROP can only occurs when the RDP is changing from level 1 to level 0. If
the user options modification tries to clear PCROP or to decrease the PCROP area, the
options programming is launched but PCROP area stays unchanged. On the contrary, it is
possible to increase the PCROP area.
When option bit PCROP_RDP is cleared, when the RDP is changing from level 1 to level 0,
Full Mass Erase is replaced by Partial Mass Erase in order to keep the PCROP area (refer
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