Handling synchronous errors during state entry in UML statecharts is non-trivial because the UML spec forbids transitions inside entry actions. Three practical firmware patterns are compared: (1) Explicit guarded transitions — simple and UML-compliant but can violate DRY in larger codebases; (2) Failure-event self-posting via a LIFO queue — keeps logic contained in one state but requires framework support and breaks with multiple error conditions; (3) Asynchronous service — converts the synchronous operation into an async one with explicit success/failure events, preferred for larger teams and complex projects despite added complexity. Each approach is evaluated with concrete trade-offs and guidance on when to apply it based on project size and team scale.
