Simple state machine with switch-case in Embedded C - Step-by-Step Execution

Concept Flow - Simple state machine with switch-case

Start

↓

Current State

↓

switch-case on State

↓

State A

↓

Action

↓

Update State

↓

Loop back to Current State

The program checks the current state, runs code for that state, updates the state, and repeats.

Execution Sample

Embedded C

enum State {STATE_A, STATE_B, STATE_C};
enum State current = STATE_A;

switch(current) {
  case STATE_A: current = STATE_B; break;
  case STATE_B: current = STATE_C; break;
  case STATE_C: current = STATE_A; break;
}

This code cycles through three states A, B, and C in order.

Execution Table

Step	Current State	switch-case branch	Action	Next State
1	STATE_A	case STATE_A	Set current = STATE_B	STATE_B
2	STATE_B	case STATE_B	Set current = STATE_C	STATE_C
3	STATE_C	case STATE_C	Set current = STATE_A	STATE_A
4	STATE_A	case STATE_A	Set current = STATE_B	STATE_B

💡 The state machine loops indefinitely cycling through states A, B, and C.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
current	STATE_A	STATE_B	STATE_C	STATE_A	STATE_B

Key Moments - 2 Insights

Why does the state change after each switch-case?

Because each case sets 'current' to the next state before breaking, as shown in the execution_table rows 1-3.

What happens if there is no 'break' after a case?

Without 'break', execution would continue to the next case, causing unexpected state changes. The execution_table shows one case per step due to breaks.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'current' after Step 2?

A STATE_C

B STATE_B

C STATE_A

D Undefined

💡 Hint

Check the 'Next State' column for Step 2 in the execution_table.

At which step does the state machine return to STATE_A?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Next State' column in the execution_table to find when 'current' becomes STATE_A.

If the 'break' statements were removed, what would happen in the execution_table?

A Each step would only execute one case as before.

B The state would update multiple times per step, skipping states.

C The state would never change.

D The program would crash.

💡 Hint

Recall that without 'break', switch-case falls through multiple cases in C.

Concept Snapshot

Simple state machine uses a variable to track state.
Use switch-case to run code based on current state.
Each case updates the state variable.
Use break to prevent fall-through.
Loop to cycle through states repeatedly.

Full Transcript

This example shows a simple state machine in embedded C using switch-case. The variable 'current' holds the current state. The switch-case checks 'current' and runs code for that state. Each case sets 'current' to the next state and breaks to stop fall-through. The execution table shows step-by-step how 'current' changes from STATE_A to STATE_B, then STATE_C, then back to STATE_A, cycling indefinitely. Key points include the importance of break statements to avoid running multiple cases at once. The visual quiz tests understanding of state changes and switch-case behavior.