
RM0453 Rev 2
125/1454
RM0453
Embedded Flash memory (FLASH)
153
When ESE = 1 and the secure hide protection area is disabled, the CPU2 debug is enabled
with the C2SWDBGEN bit after restarting OBL. However when the secure hide protection
area is enabled, the CPU2 debug is disabled with the C2SWDBGEN bit and may
subsequently be enabled by software.
4.6.5 Hide
protection area (HDPAD)
This feature is only available when the system is secure (ESE = 1).
All or a part of the Flash memory can be made hide protected, providing only access to this
Flash memory area when enabled. Once hide protection access is disabled with the
HDPADIS bit, the area is protected against execution, read and write from any bus master.
The Flash hide protect area is no longer accessible.
The hide protect area is an area in user Flash which is accessible after a reset and where all
access (execute, read, write) can be prohibited by setting the HDPADIS bit. This hide
protect register bit is be set by the hide protect code at the end of its execution. The hide
protection area is useful to provide SFU functions, only available after a device reset.
4.6.6
CPU1 boot lock chain of trust
The BOOT_LOCK forces the CPU1 to boot from the user Flash memory, regardless of what
is selected by BOOT0 and BOOT1. When BOOT_LOCK is enabled and BOOT0/BOOT1
select anything different than the user Flash memory boot, the system boots anyway from
the user Flash memory. System boot via BOOT0/BOOT1 from SRAM1 or bootloader or
CPU2 SFI/RSS boot is no longer possible.
It is still possible to boot the CPU1 according to the software selected remap by
MEM_MODE bits in
SYSCFG memory remap register (SYSCFG_MEMRMP)
or bootloader.
4.6.7
CPU2 boot lock chain of trust
When the BOOT0/BOOT1 select a CPU2 boot mode, the C2BOOT_LOCK forces the CPU2
to boot from the SBRV and C2OPT. When C2BOOT_LOCK is enabled and BOOT0/BOOT1
select system CPU2 SFI/RSSI boot, the system boots anyway from the user Flash SBRV
and C2OPT instead. In this case, CPU1 is on hold.
When C2BOOT_LOCK is enabled, SBRV and C2OPT can no longer be modified.
The C2BOOT_LOCK does not impact the CPU1 boot. CPU1 still boots according to BOOT0
and BOOT1 settings (system Flash, user Flash or SRAM1).
4.7
FLASH program erase suspension
Flash program and erase operation can be suspended by setting the PES bit in
FLASH_ACR or FLASH_C2ACR. This feature is useful when executing time critical
sections by a CPU. It makes possible to suspend any new program or erase operation from
being started, preventing CPU instruction and data fetches from being blocked.