Our daily lives are increasingly dependent on embedded systems in today’s fast-paced technological landscape. They are entrusted with critical functions that can make the difference between life and death. From autonomous vehicles on bustling streets to avionics systems guiding aircraft, these systems are entrusted with critical functions that can make the difference between life and death. Embedded systems must perform reliably even under adverse conditions or if they encounter faults, which brings us to functional safety.
The Imperative of Functional Safety
Functional safety encompasses a range of industries, with standards like ISO 26262 for the automotive industry and DO-178C for avionics. With these standards, embedded systems can be identified, mitigated, and managed in a structured way, especially for safety-critical systems.
ISO 26262: Driving Safety in the Automotive World
In the automotive industry, ISO 26262, known as the “Road Vehicles – Functional Safety” standard, is the cornerstone of safety. From concept to decommissioning, it outlines a comprehensive framework for developing safety-critical systems in vehicles. There are several key aspects to consider:
Safety Goals and Hazard Analysis: Identifying potential hazards and defining safety goals that ensure the system operates safely even in failure scenarios.
Risk Assessment: Evaluating the risks associated with these hazards, classifying them according to their severity, and defining safety integrity levels (ASILs).
Safety Lifecycle: A structured process encompassing requirements, design, implementation, and testing phases, with rigorous documentation to track safety-related activities.
Hardware and Software Development: Guidelines for designing and verifying safety-critical hardware and software components, ensuring they meet the specified safety requirements.
Verification and Validation: Rigorous testing and verification procedures, including fault injection and simulation, to validate that the system adheres to safety standards.
DO-178C: Soaring to New Heights in Avionics Safety
Functional safety in aviation is governed by DO-178C, or “Software Considerations in Airborne Systems and Equipment Certification.” This document addresses several levels of criticality for airborne software, including:
Software Levels: Categorizing software into five levels of criticality, from Level A (catastrophic) to Level E (no safety effect), based on the impact of failure.
Software Development Process: A rigorous software development process that includes planning, requirements, design, coding, testing, and verification to meet the safety objectives.
Traceability: Establishing traceability links from high-level requirements down to the low-level source code and verification test cases.
Data Coupling and Control Coupling: Ensuring that software modules are as independent as possible to minimize the risk of unexpected interactions.
Tool Qualification: Verifying and validating the tools used in the development process to ensure they don’t compromise safety.
The Quest for Fault Tolerance and Redundancy
Fault tolerance is a cornerstone of functional safety. When faults occur, this approach enables systems to continue functioning, though in a degraded manner. There are various ways to achieve resilience through redundancy, including:
Hardware Redundancy: Duplicate hardware components, such as processors or sensors, which can take over if a primary component fails.
Software Redundancy: Redundant software modules that can seamlessly switch in case of a fault.
Triple Modular Redundancy (TMR): A technique where three identical hardware components run in parallel, with a voting mechanism to select the correct output.
Diverse Redundancy: Using functionally equivalent, but architecturally diverse components to minimize common-mode failures.
Redundancy is a non-negotiable requirement in the aviation industry, for instance. Despite multiple faults, aircraft systems are designed to keep passengers and crew safe.
Conclusion
In the world of embedded systems, functional safety requires meticulous planning, unwavering attention to detail, and a commitment to mitigating risks. Our trust in technology is upheld and lives are protected by functional safety standards like ISO 26262 and DO-178C.
As embedded systems evolve, the pursuit of functional safety remains a constant, ensuring that even when the road gets rough or the skies turn turbulent, our embedded systems will be able to guide us safely.
