Realtidskrav

Real-time requirements (realtidskrav) define the timing constraints that a system must meet in its operation. They specify deadlines, response times, latency, and jitter for functions, rather than general performance. They require that certain tasks complete within a specified time window to ensure correct system behavior, especially in safety-critical or high-assurance domains. They are analyzed in terms of end-to-end timing and worst-case execution time.

They are typically categorized as hard, soft, or firm real-time. Hard real-time implies that missing a deadline constitutes a system failure and must be prevented. Soft real-time allows occasional misses with degraded quality. Firm real-time tolerates misses with significant impact, but the system remains functional.

Satisfying real-time requirements involves design and analysis: allocating time budgets to tasks, choosing scheduling policies and a real-time operating system, performing worst-case execution time analysis, and using deterministic hardware. Common scheduling approaches include fixed-priority (rate-monotonic) and dynamic-priority (earliest-deadline-first). Techniques exist to reduce jitter and ensure isolation between components.

Validation and standards: Real-time requirements are validated through analysis, simulation, and testing to verify that deadlines are met under worst-case conditions. In industry, real-time requirements intersect with safety and reliability standards such as ISO 26262 for automotive, IEC 61508 for functional safety, and DO-178C for aviation software. They are essential in embedded systems, automation, telecommunications, and control applications.