AN4266 datasheet(7/76 Pages) STMICROELECTRONICS

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AN4266

Preface

Doc ID 024283 Rev 2

7/76

Preface

This document discusses requirements and assumptions for the use of the SPC56xL70xx

Microcontroller Unit (MCU) in ASIL D applications. It prescribes several measures as

mandatory (or mandatory under certain preconditions, for example, if a certain module is

used) whereby the measure described was assumed to be in place when analyzing the

safety of the MCU.

This document considers:

●

The system assembly that contains the SPC56xL70xx MCU

●

The “Safety Element out of Context” section in the “Road vehicles - Functional safety -

Part 10: Guideline [ISO/DIS 26262-10]” standard

●

Certain assumptions about the assembly's functional safety needs based on that

standard

and determines whether a measure is mandatory or not based on these factors.

What this means for designers using the SPC56xL70xx MCU is that if they don’t fulfill a

specific Safety Application Guide (SAG) prescription they either have to show to their ISO

26262 assessor that the alternative solution is similarly efficient concerning the safety

requirement in question (for example, provides the same coverage, avoids Common Cause

Failure (CCF) as effectively, and so on), or they have to specify the increased failure

rate/reduced Safe Failure Fraction (SFF) they estimate to incur due to the deviation.

Otherwise, the assessor will not recognize the MCU certificate that the customer received

with the MCU.

This document also contains guidelines on how to configure and operate the SPC56xL70xx

for ASIL D applications. These guidelines are preceded by one of the following bold text

statements:

●

Implementation hint

●

Recommended

●

Example

These guidelines are considered to be useful approaches for the specific topics under

discussion, but are not mandatory. The user will need to use discretion in deciding whether

these measures are appropriate for their applications.

This document is valid only under the assumption that the MCU is used in automotive

applications for use cases requiring a fail-silent or a fail-indicate MCU.

Mandatory: This document is only valid if the environmental conditions given in the

SPC56xL70xx data sheet are maintained.

The cores in the SPC56xL70xx can be configured to operate in either Lock-Step Mode

(LSM) or Decoupled Parallel Mode (DPM). In LSM, the outputs of a set of replicated

modules, identified as the Sphere of Replication (SoR, see Section 2.5, Sphere of

Replication for details), are compared to ensure that the operations or transactions that are

executed are identical on a clock per clock basis.

Mandatory: This document is based on the assumption that the SPC56xL70xx is

configured to operate in LSM.

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