State machine for protocol handling in Embedded C - Mini Project: Build & Apply

State machine for protocol handling

📖 Scenario: You are working on a simple device that communicates using a protocol with three states: IDLE, RECEIVING, and PROCESSING. The device waits for a start signal, receives data, and then processes it.

🎯 Goal: Build a state machine in C that handles the protocol states and transitions correctly.

📋 What You'll Learn

Create an enum for the states: IDLE, RECEIVING, PROCESSING

Create a variable to hold the current state

Write a function to handle state transitions based on input signals

Print the current state after each transition

💡 Why This Matters

🌍 Real World

State machines are used in embedded devices to manage communication protocols, user interfaces, and hardware control.

💼 Career

Understanding state machines is essential for embedded systems engineers, firmware developers, and anyone working with hardware-software integration.

1

Define the states enum and current state variable

Create an enum called State with these exact members: IDLE, RECEIVING, PROCESSING. Then create a variable called current_state of type State and set it to IDLE.

Embedded C

// Your code here

Need a hint?

Use typedef enum { ... } State; to define states. Then declare State current_state = IDLE;.

2

Create input signal variable

Create an int variable called input_signal and set it to 0. This will represent the incoming signal to the state machine.

Embedded C

typedef enum {
    IDLE,
    RECEIVING,
    PROCESSING
} State;

State current_state = IDLE;

// Your code here

Need a hint?

Declare int input_signal = 0; to hold the signal.

3

Write the state machine function

Write a function called handle_state() that uses switch(current_state) to handle states. For each state, check input_signal and update current_state as follows:
- If current_state == IDLE and input_signal == 1, set current_state = RECEIVING.
- If current_state == RECEIVING and input_signal == 2, set current_state = PROCESSING.
- If current_state == PROCESSING and input_signal == 0, set current_state = IDLE.

Embedded C

typedef enum {
    IDLE,
    RECEIVING,
    PROCESSING
} State;

State current_state = IDLE;

int input_signal = 0;

// Your code here

Need a hint?

Use a switch statement on current_state. Inside each case, check input_signal and update current_state accordingly.

4

Print the current state after transitions

Write a main() function that sets input_signal to 1, calls handle_state(), then sets input_signal to 2, calls handle_state(), then sets input_signal to 0, calls handle_state(). After each call, print the current state as a string: IDLE, RECEIVING, or PROCESSING.

Embedded C

typedef enum {
    IDLE,
    RECEIVING,
    PROCESSING
} State;

State current_state = IDLE;

int input_signal = 0;

void handle_state() {
    switch(current_state) {
        case IDLE:
            if (input_signal == 1) {
                current_state = RECEIVING;
            }
            break;
        case RECEIVING:
            if (input_signal == 2) {
                current_state = PROCESSING;
            }
            break;
        case PROCESSING:
            if (input_signal == 0) {
                current_state = IDLE;
            }
            break;
    }
}

// Your code here

Need a hint?

Use printf to print the state name after each handle_state() call. Use if statements to check current_state.