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Impact of AUTOSAR, ISO26262 on car network design

30 Oct 2014  | Andrew Patterson

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Today's safety standards pave the way for closer technical collaboration across the automotive industry with the added benefit of reducing costs and development times, and the opportunity to limit miscommunication of technical specifications. This article looks at some of the detail of ISO26262 and AUTOSAR, and how they are supporting each other as automotive OEMs look to increase the use of embedded software components.

ISO26262 – what is it?
ISO 26262 is a derivative of the more generally applied IEC 61508 functional-safety standard for electrical and electronic systems for road vehicles. It addresses specifically automotive electronic and electrical safety-related systems, and is applicable throughout the design, development, and manufacturing cycle, as well as for relationships between automotive companies and their suppliers. ISO26262 is targeted at vehicles up to 3500Kg in weight, and seeks to minimise the potential hazards caused by malfunctioning or failure of the embedded electronic and electrical systems. The standard uses the concept of "ASIL" (Automotive Safety Integrity Level) to classify the safety requirements of each and every sub-system in the vehicle – these are graded from A (least critical) to D (most critical); it also defines a concept of "QM" (Quality Managed) for items that might not be safety relevant or have a very low potential for impacting overall system safety.

The automotive supply ecosystem is changing rapidly to adopt the concepts of ISO26262, and demonstration of compliance is increasingly being mandated by manufacturers in their RFQs (Request for Quotes). Proving compliance is not straight-forward and a collection of proof-point artefacts is typically produced and delivered with the supplied product to demonstrate that ISO26262 requirements have been addressed. The requirements specifically for software developers and software tool suppliers are specified in part 6 of the ISO26262 standard – often a software delivery will be "out of context" of the overall automotive system being proven. Components developed in isolation from their final destination system are allowed for in ISO26262 and are so called "Safety Elements out of Context" (SEooC).

For an embedded software developer, the ISO26262 requirement covers many different points in the product lifecycle, these include: requirements capture, coding, and development; test strategy design; test execution; system documentation; and assembling a set of documentation and evidence that can demonstrate that a repeatable and reliable process has been followed.

Table 1: ASIL classification and in-car examples.

Safety concerns
The ASIL classification of in-vehicle components in turn defines how much effort must be put into ensuring safety and reliability. ASIL A requires less effort that ASIL D. If the car radio fails, it is annoying, so a Quality Management (QM) classification may be appropriate. If the steer-by-wire system fails, it could have catastrophic consequences, and failsafe operation is expected with built-in redundancy; this expectation ties into an ASIL D designation. For each safety-related item, the impact of failure is considered, along with the controllability of the system, and the probability of exposure of a failure to the driver during normal operation of the vehicle (note that even high probability events would be extremely rare; on the order of one failure per one million hours of operation). The degree to which each of these factors ties in with the ASIL classification is given in table 1.

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