State Machines and Protocol Implementation Questions

Explain how to design, document, and implement finite state machines for device drivers and communication protocols. Include state diagrams, table driven implementations, deterministic transitions, event queue handling, timeout and error recovery strategies, and memory efficient encodings of state. Cover parsing and framing, sequence handling, retransmission and flow control, and how state machines integrate with interrupts and deferred work. Describe testing approaches such as unit tests for state transitions, simulation, fault injection, and how to reason about corner cases and livelock or dead states.