Functional Safety offers the required risk-reduction to assure safety in the presence of systematic or random faults.
Systematic failures happen due to a design flaw and are present in all implementations. Engineers take care of these using Quality Management Systems (QMS) to trace the design and development methodologies, the manufacturing process, the operational procedures, the documentation, and other relevant factors used on the overall system.
Random failures are transient faults or soft errors such as radiation, EMI, or power glitches; permanent errors caused by power shortages or others; dependant faults due to failures or related to components within the system; or potential faults where the impact is not seen for some time. Engineers addressed those using a combination of self-test capability, hardware safety mechanisms, and functional redundancy.
Failure Modes and Effects Analysis (FMEA) allows to identify and evaluate the effects of both systematic and random failure modes on applications, eliminate or reduce the chance of failure, and to document the system development process. A Failure Modes, Effects and Diagnostic Analysis (FMEDA) is an FMEA extension that includes quantitive failure data (fault rates and the distribution of failure modes) for all components analyzed in the application and the probability of the safety system design to detect internal failures using online diagnostics techniques. FMEDAs are based on the MIL-STD-1629A standard and were developed in the late 1980s by Dr. William M. Goble and engineers from exida.
FMEDAs are a structured quantitative analysis of a system, subsystem, product, or component; and are used to predict failure rates, failure modes, and their effects on (system) operation, while considering potential diagnostic functions. Also, design, development, and verification engineering teams generate FMEDAs to ensure all the ISO 26262 documentation and traceability requirements are met in the SoC development flow, at both the IP and the full-chip level.
Failure Modes, Effects and Diagnostic Analysis take into consideration:
- All the components included in the design
- The functionality of each component
- The failure modes of each component
- The effect of each component failure mode on the product functionality
- The ability to detect the failure of any automatic diagnostics
- The design strength (de-rating, safety factors)
- The operational profile (environmental stress factors).
FMEDAs make safer applications by helping to predict the failure mode data and the product level failure rate for a product. FMEDAs use component database calibrated with reasonably accurate field failure rate and failure modes, that are more accurate than field warranty return analysis or field failure analysis —because these methods depend on reports that typically do not have enough detail information in failure records.