Event-driven state machine in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the initial state of the state machine.

Embedded C

typedef enum {STATE_IDLE, STATE_RUNNING, STATE_STOPPED} State;

State current_state = [1];

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ASTATE_IDLE

BSTATE_UNKNOWN

CSTATE_STOPPED

DSTATE_RUNNING

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a running or stopped state as initial state.

The initial state of the state machine is usually set to STATE_IDLE to indicate it is waiting for events.

2fill in blank

medium

Complete the code to declare the event type for the state machine.

Embedded C

typedef enum {EVENT_START, EVENT_STOP, [1] Event;

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AEVENT_PAUSE

BEVENT_RUN

CEVENT_IDLE

DEVENT_RESET

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing events that are not typical for resetting state machines.

EVENT_RESET is a common event used to reset the state machine to its initial state.

3fill in blank

hard

Fix the error in the state transition function to handle the STOP event.

Embedded C

void handle_event(Event event) {
    switch(current_state) {
        case STATE_RUNNING:
            if(event == [1]) {
                current_state = STATE_STOPPED;
            }
            break;
        default:
            break;
    }
}

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AEVENT_START

BEVENT_RESET

CEVENT_STOP

DEVENT_PAUSE

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong event name for stopping the machine.

The EVENT_STOP triggers the transition from STATE_RUNNING to STATE_STOPPED.

4fill in blank

hard

Fill both blanks to complete the state transition for the RESET event.

Embedded C

void handle_event(Event event) {
    switch(current_state) {
        case STATE_STOPPED:
            if(event == [1]) {
                current_state = [2];
            }
            break;
        default:
            break;
    }
}

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AEVENT_RESET

BEVENT_START

CSTATE_IDLE

DSTATE_RUNNING

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the reset event or state with start or running states.

The EVENT_RESET event resets the state machine back to STATE_IDLE.

5fill in blank

hard

Fill all three blanks to implement the event-driven state machine loop.

Embedded C

while(1) {
    Event event = get_next_event();
    switch(current_state) {
        case STATE_IDLE:
            if(event == [1]) {
                current_state = [2];
            }
            break;
        case STATE_RUNNING:
            if(event == [3]) {
                current_state = STATE_STOPPED;
            }
            break;
        default:
            break;
    }
}

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AEVENT_START

BSTATE_RUNNING

CEVENT_STOP

DSTATE_IDLE

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up event names or states in the transitions.

The machine starts running on EVENT_START from STATE_IDLE, and stops on EVENT_STOP from STATE_RUNNING.