Introduction

In the world of automotive functional safety, ISO 26262 mandates rigorous safety mechanisms to detect, mitigate, or prevent failures. However, what happens when the safety mechanism itself fails? Can we blindly trust that an error-detecting system will always work? This is where latent safety mechanisms come into play—designed to verify the integrity of primary safety mechanisms. This blog explores the problem of undetected failures in safety mechanisms and why checking the checker is crucial for ISO 26262 compliance.

Problem Statement: The Hidden Risk in Safety Mechanisms

Modern automotive electronics rely on safety mechanisms such as ECC (Error Correction Code), CRC (Cyclic Redundancy Check), watchdog timers, and lockstep processing to detect and correct failures. However, these mechanisms themselves can fail due to:

1. Silent Failures: A failed error-checking mechanism might not raise any alarms, leaving faults undetected.
2. Aging and Degradation: Hardware components degrade over time, potentially leading to unreliable detection.
3. Systematic Errors: Design flaws in safety mechanisms can lead to false positives or missed detections.
4. Fault Masking: Multiple faults occurring together might cancel each other out, leading to an incorrect system state.

If these failures go unnoticed, they become latent faults—errors that remain hidden until a secondary failure leads to a catastrophic event. ISO 26262 Part 5 specifically addresses the need for latent safety mechanisms to monitor and validate primary safety mechanisms to prevent such situations.

Conclusion

A robust safety system should not only detect faults but also verify its own effectiveness. The next step is to explore how latent safety mechanisms can be implemented to check the checker and ensure functional safety in compliance with ISO 26262. Stay tuned for the solution in our next blog post.