STM32L552CC_V01 datasheet(53/340 Pages) STMICROELECTRONICS

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DS12737 Rev 6

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STM32L552xx

Functional overview

TrustZone security

When the TrustZone security is activated by the TZEN option bit, the RCC is switched in

TrustZone security mode.

The RCC TrustZone security allows to secure some RCC system configuration and

peripheral configuration clock from being read or modified by non-secure accesses:

•

RCC system security:

–

HSE, HSE-CSS, HSI, MSI, LSI, LSE, LSE-CSS, HSI48 configuration and status

bits

–

Main PLL, PLLSAI1, PLLSAI2, AHB prescaler configuration and status bits

–

System clock SYSCLK and HSI48 source clock selection and status bits

–

MCO clock output configuration and STOPWUCK bit

–

Reset flag RMVF configuration bit

•

RCC peripheral security:

–

When a peripheral is secure, the related peripheral clock, reset, clock source

selection and clock enable during low power modes control bits are secure.

•

A peripheral is in secure state when:

–

For securable peripherals, when it's corresponding SEC security bit is set in the

TZSC (TrustZone security controller)

–

For TrustZone-aware peripherals, a security feature of this peripheral is enabled

through its dedicated bits.

3.12

Clock recovery system (CRS)

The devices embed a special block which allows automatic trimming of the internal 48 MHz

oscillator to guarantee its optimal accuracy over the whole device operational range. This

automatic trimming is based on the external synchronization signal, which could be either

derived from USB SOF signalization, from LSE oscillator, from an external signal on

CRS_SYNC pin or generated by user software. For faster lock-in during startup it is also

possible to combine automatic trimming with manual trimming action.

3.13

General-purpose inputs/outputs (GPIOs)

Each of the GPIO pins can be configured by software as output (push-pull or open-drain), as

input (with or without pull-up or pull-down) or as peripheral alternate function. Most of the

GPIO pins are shared with digital or analog alternate functions.

After reset, all GPIOs are in Analog mode to reduce power consumption.

The I/Os alternate function configuration can be locked if needed following a specific

sequence in order to avoid spurious writing to the I/Os registers.

GPIO TrustZone security

Each I/O pin of GPIO port can be individually configured as secure. When the selected I/O

pin is configured as secure, its corresponding configuration bits for alternate function, mode

selection, I/O data are secure against a non-secure access. The associated registers bit

access is restricted to a secure software only. After reset, all GPIO ports are secure.

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