State Machines in Embedded Systems are fundamental in designing and implementing efficient, reliable, and robust systems. It’s a programming technique that brings structure, predictability, and efficiency to an embedded system’s response to multiple events and states.
In embedded systems states, machines are used in the design and implementation. They can manage complicated logic and system behavior by responding to inputs and conditions.
This blog post aims to provide a complete beginner’s guide to understanding and executing state machines in embedded systems. We will examine state machines’ definitions, importance in embedded systems, basic concepts, design and implementation strategies, and real-world applications.
What is a State Machine?
A state machine, also known as a Finite State Machine (FSM), is a mathematical model of computation. It is an abstract machine that can be in one of a finite number of states. Embedded systems are reactive by nature, so a state machine represents the system’s behavior. A system can be any electronic system, software, or another system. It has a set of states representing each mode of system or specific condition, and the transition between them determines the system’s actual behavior.
Image Captions: State transitions of a traffic light system
Types of State Machines
There are several types of state machines but some of the important types are mentioned below:
Mealy Machine
A Mealy machine is a state machine where the current state and the input specify the outputs. This indicates that the production of a Mealy machine can change dynamically based on its input.
Moore Machine
In contrast, a Moore machine is a state machine where the current state decides the outputs alone. This means that the production of a Moore machine only changes when the state changes.
Hierarchical State Machine (HSM)
A Hierarchical State Machine (HSM) supports nested states, allowing for complex hierarchies. Its outputs can vary and are typically based on the current state and input.
Finite State Machine with Data (FSMD)
A Finite State Machine is a state machine that includes operations on data values. The outputs are determined by the current state, input, and data, and can change based on state and data operations.
UML Statecharts
UML statecharts are similar to Harel but are defined within the Unified Modeling Language (UML) context. They support advanced features like entry and exit actions and activities within states. The current state and input typically determine the outputs.
Here’s a simple table that compares these different types of state machines:
| Type | Output Dependency | Output Change | Characteristics |
| Mealy Machine | Current state and input | Dynamically with input changes | Outputs depend on state and inputs |
| Moore Machine | Current state | Only when the state changes | Outputs depend solely on the state |
| Hierarchical State Machine (HSM) | Varies (state and input) | Based on hierarchical state changes | Supports nested states, complex hierarchies |
| Finite State Machine with Data (FSMD) | Current state, input, and data | Based on state and data operations | Includes operations on data values |
| UML Statecharts | Current state, input, hierarchical/concurrent state conditions | Based on state changes and UML-specific features | Extends traditional state machines with UML features like hierarchical, concurrent, and historical states |
Caption: Compassion table for state machine types & their difference
Basic Concepts of State Machines
Understanding the basic concepts of state machines, including states, transitions, events, and actions, is crucial for their effective implementation in embedded systems.
- States: In the context of state machines, a state represents a condition or situation during the life of an object or system.
- Transitions: Transitions are the bridges between states. A transition represents the shift from one state to another. Events trigger transitions and can result in actions.
- Events: Events are occurrences or changes in the system that trigger transitions. An event could be a user input, a timer expiration, or any other condition that affects the system’s state.
- Actions: Actions are activities that occur based on the system’s state or as a result of a transition. Examples might include turning on a light, starting a motor, or performing any other operation performed by the system.
Importance of State Machines in Embedded Systems
State machines play a critical role in embedded systems. They offer several benefits that make them an essential tool for developers.
Efficiency
State machines enhance the efficiency of embedded systems. They provide a clear and structured way to design the system’s behavior, making it easier to understand and optimize. By clearly defining the system’s states and transitions, developers can minimize redundant operations and ensure that the system performs only necessary actions, thereby improving the system’s overall efficiency.
Simplification of Complex Control Logic
State machines are excellent tools for simplifying complex control logic. They allow developers to break down a complex system into a set of distinct states and transitions, making the system easier to understand and manage. This is particularly useful in embedded systems, where control logic can become extremely complex due to the interaction of multiple components and subsystems.
Reliability
State machines improve the reliability and predictability of embedded applications. By defining clear states and transitions, state machines ensure that the system behaves predictably under different conditions. This makes it easier to test the system and identify potential issues, leading to more reliable and robust applications.
State Machine Design for Embedded Systems
Designing state machines for embedded systems involves several steps, from understanding the system requirements to creating state transition diagrams and state tables.
Requirements Gathering
The first step in designing a state machine is to understand the system requirements. This involves identifying the system’s states, the events that trigger transitions between states, and the actions that occur as a result of these transitions.
State Diagram
Once the system requirements are understood, the next step is to create a state diagram. A state diagram is a graphical representation of the state machine, showing the states, transitions, and actions. It provides a clear visual overview of the system’s behavior.
State Table
In addition to the state diagram, a state table can be used for design clarity. A state table is a tabular representation of the state machine, listing the states, inputs, and resulting next states and outputs. It provides a concise and easy-to-read overview of the system’s behavior.
Example Case Study
The IoT-enabled water monitoring system in the below diagram starts in Idle. It moves to Measuring to collect data, then to Analyzing to assess it. If an issue is found, it transitions to Alerting; otherwise, it sends data to the cloud in Sending Data before returning to Idle. If inactive, the system transitions to Sleeping to save power, and waking as needed to resume monitoring.
Image Caption: Water Monitoring System State Machine
Implementing State Machines in Embedded Systems
Once the design of the state machine is complete, the next step is to implement it in the embedded system. This involves choosing a programming language, organizing the code, and selecting an implementation strategy.
Programming Languages
State machines can be implemented in various programming languages. The choice of language depends on the specific requirements of the Embedded systems programming. Common languages used for implementing state machines in embedded systems include C and C++.
Code Structure
Organizing the code for state machines involves defining the states, events, and actions, and writing the logic for the transitions. The code should be structured in a way that makes it easy to understand and modify.
Implementation Strategies
There are several strategies for implementing state machines. These include using switch-case statements, state tables like the Lookup table method, function pointer, switch case, and state design patterns. The choice of strategy depends on the complexity of the state machine and the specific requirements of the embedded system.
Code Example
Here’s a simple code snippet implementing a state machine in C:
“typedef enum { STATE_A, STATE_B, STATE_C } state_t;
state_t state = STATE_A;
while (1) {
switch (state) {
case STATE_A:
// Perform actions for state A
if (/* condition */) {
state = STATE_B;
}
break;
case STATE_B:
// Perform actions for state B
if (/* condition */) {
state = STATE_C;
}
break;
case STATE_C:
// Perform actions for state C
if (/* condition */) {
state = STATE_A;
}
break;
}
}”
Tools and Libraries for State Machine Development
There are various tools and libraries available that can aid in the development of state machines for embedded systems. These tools can help in designing, implementing, and testing state machines.
State Machine Tools
State machine tools provide graphical interfaces for designing state machines. They allow you to create state diagrams and automatically generate code based on the design. Some popular state machine tools include Stateflow (a toolbox in MATLAB), UML diagrams tools like Visual Paradigm, and YAKINDU Statechart Tools.
Libraries and Frameworks
There are also several libraries and frameworks available for implementing state machines in various programming languages. These libraries provide pre-defined classes and functions for defining states, transitions, and actions, making it easier to implement state machines. Some popular libraries and frameworks for state machines in embedded systems include the Quantum Framework (for C/C++), Boost Statechart (for C++), and PyTransitions (for Python).
Real-World Applications of State Machines in Embedded Systems
State machines are widely used in real-world embedded systems across various industries. Here are a few examples:
Automotive Systems
In automotive systems, state machines are used in components like engine control units and infotainment systems. For example, an engine control unit might have states for idling, accelerating, cruising, and decelerating, with transitions triggered by inputs like the accelerator pedal position and the current speed.
Image Caption: Automotive Engine Control Unit
Consumer Electronics
State machines are also common in consumer electronics like smartphones and washing machines. For instance, a washing machine might have states for filling, washing, rinsing, and spinning, with transitions triggered by timers or sensors.
Image Caption: State Diagram of Washing Machine
Industrial Automation
In industrial automation, state machines are used in systems like robotics and manufacturing systems. For example, a robotic arm might have states for idle, pick up, move, and place, with transitions triggered by sensors or control signals.
Image Caption: State Diagram of Industrial Robotic Arm
Future Trends in State Machines and Embedded Systems
Advances in State Machine Theory
New research can change the dynamics of state machine theory and address complex issues by developing new methodologies. Recent advancements in the formal verification field are to prove the correctness of state machine design can help remove bugs and make sure the system can react accurately under all the possible conditions. Another recent development is an area of real time constraint and handling coincidence which are the most common challenges in embedded systems.
Integration with AI and Machine Learning
Artificial intelligence (AI) and machine learning (ML) are recent trends in embedded systems. AI and ML can be used to track data to make intelligent decisions, while state machines can manage system behavior in a structured way. For example, a state machine in a self-driving vehicle can operate in the following modes of operation (e.g., parked, driving, overtaking, stopping). AI/ML can use computer vision to interpret data from cameras and sensors for planning, prediction, perception, and learning. This combination of state machines and AI/ML can lead to embedded systems that are efficient and reliable and capable of adapting to their environment and improving their performance over time.
Evolving Standards and Practices
As the field of embedded systems continues to grow, we’re witnessing the emergence of new standards and best methods for the design and implementation of state machines. These include guidelines for state machine modeling, coding standards for state machine implementation, and testing methodologies to ensure the correctness and reliability of state machine designs. These evolving standards and practices are helping to improve the quality of embedded systems and make it easier for engineers to design, implement, and maintain state machines.
Conclusion
State machines in embedded systems are fundamental concepts that can be utilized to design a reliable and robust system. State machines can provide a clear and structured way to design the system’s behavior to understand performance against different states or conditions better.
At Devomech Solutions, we use state-machine concepts and apply them to real world projects for different industries. Our main focus is to build a system that can react to a wide range of scenarios in real time with the help of our expert engineers.
We invite you to explore our portfolio to see some of the innovative solutions we’ve developed using state machines and other advanced technologies. If you want to learn more about how we can help you with your next project, please don’t hesitate to contact us.
