Datasheet

Functional overview STM32L496xx
22/272 DS11585 Rev 9
The Firewall main features are the following:
• Three segments can be protected and defined thanks to the Firewall registers:
– Code segment (located in Flash or SRAM1 if defined as executable protected
area)
– Non-volatile data segment (located in Flash)
– Volatile data segment (located in SRAM1)
• The start address and the length of each segments are configurable:
– Code segment: up to 1024 Kbyte with granularity of 256 bytes
– Non-volatile data segment: up to 1024 Kbyte with granularity of 256 bytes
– Volatile data segment: up to 256 Kbyte of SRAM1 with a granularity of 64 bytes
• Specific mechanism implemented to open the Firewall to get access to the protected
areas (call gate entry sequence)
• Volatile data segment can be shared or not with the non-protected code
• Volatile data segment can be executed or not depending on the Firewall configuration
The Flash readout protection must be set to level 2 in order to reach the expected level of
protection.
3.8 Boot modes
At startup, BOOT0 pin and nBOOT1 option bit are used to select one of three boot options:
• Boot from user Flash
• Boot from system memory
• Boot from embedded SRAM
BOOT0 value may come from the PH3-BOOT0 pin or from an option bit depending on the
value of a user option bit to free the GPIO pad if needed.
A Flash empty check mechanism is implemented to force the boot from system flash if the
first flash memory location is not programmed and if the boot selection is configured to boot
from main flash.
The boot loader is located in system memory. It is used to reprogram the Flash memory by
using USART, I2C, SPI, CAN or USB OTG FS in Device mode through DFU (device
firmware upgrade).
3.9 Cyclic redundancy check calculation unit (CRC)
The CRC (cyclic redundancy check) calculation unit is used to get a CRC code using a
configurable generator polynomial value and size.
Among other applications, CRC-based techniques are used to verify data transmission or
storage integrity. In the scope of the EN/IEC 60335-1 standard, they offer a means of
verifying the Flash memory integrity. The CRC calculation unit helps compute a signature of
the software during runtime, to be compared with a reference signature generated at link-
time and stored at a given memory location.
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