STM32F412XE datasheet(20/193 Pages) STMICROELECTRONICS

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Functional overview

STM32F412xE/G

20/193

DocID028087 Rev 4

3.4

Memory protection unit

The memory protection unit (MPU) is used to manage the CPU accesses to memory to

prevent one task to accidentally corrupt the memory or resources used by any other active

task. This memory area is organized into up to 8 protected areas that can in turn be divided

up into 8 subareas. The protection area sizes are between 32 byte and the whole 4 Gbyte of

addressable memory.

The MPU is especially helpful for applications where some critical or certified code has to be

protected against the misbehavior of other tasks. It is usually managed by an RTOS (real-

time operating system). If a program accesses a memory location that is prohibited by the

MPU, the RTOS can detect it and take action. In an RTOS environment, the kernel can

dynamically update the MPU area setting, based on the process to be executed.

The MPU is optional and can be bypassed for applications that do not need it.

3.5

Embedded Flash memory

The devices embed up to 1 Mbyte of Flash memory available for storing programs and data.

The Flash user area can be protected against reading by an entrusted code (Read

Protection, RDP) with different protection levels.

The flash user sectors can also be individually protected against write operation.

Furthermore the proprietary readout protection (PCROP) can also individually protect the

flash user sectors against D-bus read accesses.

(Additional information can be found in the product reference manual).

To optimize the power consumption the Flash memory can also be switched off in Run or in

Sleep mode (see Section 3.21: Low-power modes).

Two modes are available: Flash in Stop mode or in DeepSleep mode (trade off between

power saving and startup time.

Before disabling the Flash, the code must be executed from the internal RAM.

3.6

One-time programmable bytes

A one-time programmable area is available with16 OTP blocks of 32 bytes. Each block can

be individually locked

(Additional information can be found in the product reference manual)

3.7

CRC (cyclic redundancy check) calculation unit

The CRC (cyclic redundancy check) calculation unit is used to get a CRC code from a 32-bit

data word and a fixed generator polynomial.

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 software

signature during runtime, to be compared with a reference signature generated at link-time

and stored at a given memory location.

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