How is Worst-Case Execution Time (WCET) determined?

WCET is the maximum time a piece of code can take to execute, critical for real-time system analysis. Methods: Static analysis: Analyze code and hardware timing without execution. Tools (aiT, Bound-T) model processor pipeline, caches, branches. Conservative but sound (safe upper bound). Requires accurate hardware model. Measurement-based: Execute code with various inputs, measure actual times. Add safety margin to observed maximum. May miss worst-case path (unsound). Easier for complex modern processors. Hybrid approach: Combine static analysis with measurements. Challenges: Modern processors have variable timing (caches, branch prediction, out-of-order execution). Pipeline state depends on history. Interrupt interference. Multi-core interference on shared resources. Mitigation: Use locked caches, disable branch prediction for critical code, time isolation on multi-core, statistical approaches (pWCET).