STM32U535NET3QTR datasheet(25/278 Pages) STMICROELECTRONICS

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DS14217 Rev 1

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STM32U535xx

Functional overview

3.4.2

Additional flash memory protections when TrustZone activated

When the TrustZone security is enabled through option bytes, the whole flash memory is

secure after reset and the following protections are available:

•

non-volatile watermark-based secure flash memory area

The secure area can be accessed only in Secure mode. One area per bank can be

selected with a page granularity.

•

secure HDP (hide protection area)

It is part of the flash memory secure area and can be protected to deny an access to

this area by any data read, write and instruction fetch. For example, a software code in

the secure flash memory hide protection area can be executed only once and deny any

further access to this area until next system reset. One area per bank can be selected

at the beginning of the secure area.

•

volatile block-based secure flash memory area

Each page can be programmed on-the-fly as secure or nonsecure.

3.4.3

FLASH privilege protection

Each flash memory page can be programmed on-the-fly as privileged or unprivileged.

Backup registers

0.5

Yes

N/A

Yes(2)

N/A(8)

Yes

N/A

N/A(8)

Yes

N/A

SRAM2/backup

RAM

0.5

Yes

N/A

Yes(2)

N/A(9)

Yes

N/A

N/A(9)

Yes

N/A

1. When the protection level 2 is active, the debug port and the bootloader mode are disabled.

2. Depends on TrustZone security access rights.

3. The system memory is only read-accessible, whatever the protection level (0, 1 or 2) and execution mode.

4. Option bytes are only accessible through the flash memory registers and OPSTRT bit.

5. The flash main memory is erased when the RDP option byte regresses from level 1 to level 0.

6. SWAP_BANK option bit can be modified.

7. OTP can only be written once.

8. The backup registers are erased when RDP changes from level 1 to level 0.

9. All SRAMs are erased when RDP changes from level 1 to level 0.

Table 4. Access status versus protection level and execution modes when TZEN = 1 (continued)

Area

RDP

level

User execution

(boot from flash memory)

Debug/ bootloader(1)

Read

Write

Erase

Read

Write

Erase

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