Case study: Selection of SoC components with ISO 26262 Part 11
This week I would like to present a case study on the selection of safety-critical components in the automotive environment. More and more vehicles are using single-chip systems (SoC). In the following, I will therefore show how the ISO 26262 Part 11 guideline can help.
InCompliance magazine has published a more detailed description of this case study: Applying ISO 26262 to Power Management in Advanced Driver Assistance Systems.
ISO 26262, Part 11
ISO 26262, Road vehicles - Functional safety, was revised in 2018. Among other things, Part 11 was added, Guidelines on application of ISO 26262 to semiconductors. This is a guideline that regulates the implementation of Part 5 (Product development at the hardware level) concretized.
The above-mentioned case study deals with the trend of reducing redundancies by combining many functions. Part 11 helps to find a solution for these single-chip systems (System-on-a-Chip, SoC) to demonstrate functional safety.
SoCs have many advantages, but they postpone the proof of concept. functional safety from the OEM to the chip manufacturer. This results in a complex interaction between the two partners.
Case study: Power management
The article describes a hypothetical situation involving the quality management of a simple DC/DC converter. This is part of an SoC. The developer or safety manager must select an SoC for which functional safety is guaranteed. According to ISO 26262, there are three analysis techniques for this:
- Block diagram - The block diagram helps the designer to create a clear structure through abstraction. For example, each block should have exactly one function. When analyzing security, the diagram helps to understand the flow of information.
- Dependent Failure Analysis (DFA) - This analysis tool is designed to help identify dependent errors between security mechanisms and the components they are intended to protect.
- Failure Mode Effects and Diagnostics Analysis (FMEDA) - FMEDA takes into account generally accepted failure modes such as interrupted resistance chains and component drift and determines the effects on the function of the device. It is also used to calculate the safety coverage for an ASIL rating.
These technologies are not only about ensuring functional safety, but also about ensuring the safety of the SoC through the clever selection of the SoC. Complexity of the system. The article from InCompliance linked above contains specific examples of all three analysis techniques.
Safety analysis for component selection
The architecture in conjunction with the initial analyses enables an initial comparison with the data sheets of possible components. At the same time, we can now examine the system functions in the context of the architecture. With the help of the DFA and the block diagram, we can identify "single points of failure" and resolve them by extending the architecture.
In this way, we can iteratively expand our architecture and identify suitable components at the same time. However, a quantitative analysis for comparing the failure probabilities with the specifications from ISO 26262 is still missing.
Conclusion
Functional safety is a constantly evolving area of automotive and industrial design. The performance of available components is remarkable, but we must be careful in our selection. With each new design comes a new set of safety mechanisms that need to be aligned with design and safety teams. Without some basic knowledge, this can lead to confusion - and downstream problems!
ISO 26262 has long been a good foundation for the development of safe vehicles. Part 11 is a solid tool that takes into account the trend towards SoCs in vehicles and provides good specifications.
