How to Effectively Implement State Machines in C: A Comparison of Techniques?

State Machine Design in C

Problem Exploration:

In the realm of embedded systems, state machines are essential for managing complex event-driven behaviors. This question explores proven implementation techniques for designing effective state machines in C.

Implementation Techniques:

Struct Array and Loop Approach:

This classic approach utilizes a struct array, known as a "transition table," to define the state machine's behavior. Each struct entry represents a transition and consists of:

• Current state (st)
• Event (ev)
• Function (fn) that returns the new state

In a loop, the state machine evaluates incoming events against the transitions. If a match is found, the specified function is executed, and the state changes accordingly.

Transition Table and Dispatcher Design:

This approach introduces an "event pump" which collects events. These events are passed to an "event integrator" which determines the next state based on a transition table. The transition table maps event-state combinations to "dispatcher" functions. The dispatcher functions invoke "actions" which update the machine's state and perform desired operations.

Benefits of the Struct Array Approach:

• Simple to implement
• Easy to maintain and modify
• Can handle nested state hierarchies

Benefits of the Transition Table and Dispatcher Design:

• Decouples events from actions
• Facilitates extensibility by adding new actions or events
• Supports multiple state machines running concurrently

Additional Design Considerations:

• Use macros to define states and events (e.g., #define ST_INIT 0)
• Employ "wildcards" (e.g., ST_ANY) to handle transitions in any state
• Ensure that all possible transitions are defined
• Pass a state machine context structure to functions to avoid global variables (useful for running multiple instances)

The above is the detailed content of How to Effectively Implement State Machines in C: A Comparison of Techniques?. For more information, please follow other related articles on the PHP Chinese website!