AN4266 datasheet(49/76 Pages) STMICROELECTRONICS

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AN4266

Functional safety requirements for application software

Doc ID 024283 Rev 2

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The RCCUs are only enabled when the SPC56xL70xx is in LSM. Application software must

determine whether LSM mode is activate. Please refer to Section 3.2.2, Checking for further

details.

3.19

Cyclic Redundancy Checker Unit (CRC)

The CRC module computes CRC checksums, which offloads the CPU. The CRC has the

capability of processing two CRC calculations simultaneously.

Recommended: The CRC module should be used to detect accidental alteration of data

during transmission or storage. The CRC takes as its input a data stream of any length and

produces a 32-bit output value.

Mandatory: The CRC calculation shall be executed to verify the content of the registers.

Note:

Rationale: The contents of the configuration registers of the safety-related modules must

be checked within the FTTI.

Note:

Theoretically, the CPU could be used instead of the CRC to verify that the value of the

configuration registers have not changed. However, using the CRC is more effective.

Note:

Implementation hint: The CRC of the configuration registers of the modules involved with

the safety function shall be calculated offline.

At run time, the same CRC value shall be calculated by the CRC module within the safety

process time. To avoid overloading the CPU, the eDMA module can be used to support the

data transfer from the registers under check to the CRC module.

The result of the runtime computation is then compared to the value of the offline CRC.

The application must include detection, or protection measures, against possible faults of

the CRC module only if the CRC module is used by any SEF.

3.20

Clock Monitor Unit (CMU)

The main task of the Clock Monitor Unit (CMU) is to supervise the integrity of various clock

sources.

Mandatory: The following supervisor functions shall be used:

●

Loss of external crystal oscillator clock

●

FMPLL frequency higher than a (programmable) value set as high reference

●

FMPLL frequency lower than a (programmable) value set as low reference

Note:

Rationale: To monitor the integrity of the clock signals

This error information is forwarded to the FCCU and to the MC_RGM.

SPC56xL70xx includes three CMUs:

●

CMU_0 monitors the clock signal of the SoR modules and the clock from the XOSC

(XOSC_CLK).

●

CMU_1 monitors the clock signal used by the motor control related peripherals (such

as eTimer, FlexPWM, CTU and ADC).

●

CMU_2 monitors the clock signal for the protocol engine of the FlexRay module.

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