STM32L4P5CE datasheet(22/311 Pages) STMICROELECTRONICS

22 / 311 page

Functional overview

STM32L4P5xx

22/311

DS12903 Rev 2

Either 64 Kbytes or 4 Kbytes of SRAM2 can be retained in Standby mode.

The SRAM2 can be write-protected with 1 Kbyte granularity.

•

128 Kbytes mapped at address 0x2003 0000 (SRAM3).

The memory can be accessed in read/write at CPU clock speed with 0 wait states.

3.5

Boot modes

At startup, a BOOT0 pin and an nBOOT1 option bit are used to select one of three boot

options:

•

Boot from user Flash

•

Boot from system memory

•

Boot from embedded SRAM

The 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 the system memory. It is used to reprogram the Flash memory

by using USART, I2C, SPI, CAN or USB OTG FS in device mode through the DFU (device

firmware upgrade).

3.6

Firewall

These devices embed a firewall which protects code sensitive and secure data from any

access performed by a code executed outside of the protected areas.

Each illegal access generates a reset which kills immediately the detected intrusion.

The main features of the firewall 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 segment are configurable:

–

Code segment: up to 1024 Kbytes with granularity of 256 bytes

–

Non-volatile data segment: up to 1024 Kbytes with granularity of 256 bytes

–

Volatile data segment: up to 128 Kbytes 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.

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