Polling vs interrupt-driven execution in Embedded C - Hands-On Comparison

Polling vs Interrupt-Driven Execution in Embedded C

📖 Scenario: You are working on a simple embedded system that reads a button press to toggle an LED. You want to understand the difference between polling and interrupt-driven execution.

🎯 Goal: Build two small programs: one using polling to check the button state repeatedly, and another using an interrupt to react to the button press immediately.

📋 What You'll Learn

Create a variable to represent the button state

Create a variable to represent the LED state

Write a polling loop to check the button state and toggle the LED

Write an interrupt service routine (ISR) to toggle the LED on button press

Print the LED state changes to simulate output

💡 Why This Matters

🌍 Real World

Embedded systems often need to read buttons or sensors. Polling checks repeatedly, which can waste time. Interrupts react immediately, saving power and improving responsiveness.

💼 Career

Understanding polling vs interrupts is key for embedded software engineers working on microcontrollers, IoT devices, and real-time systems.

1

Setup button and LED state variables

Create two integer variables called button_state and led_state. Initialize button_state to 0 (not pressed) and led_state to 0 (LED off).

Embedded C

# Create variables button_state and led_state with initial values
# Your code here

Need a hint?

Use int type and set both variables to 0.

2

Add a polling loop to check button state

Add a while(1) infinite loop. Inside it, use an if statement to check if button_state equals 1 (pressed). If pressed, toggle led_state between 0 and 1 using led_state = 1 - led_state;. Then reset button_state to 0.

Embedded C

int button_state = 0;
int led_state = 0;

// Add polling loop to check button_state
# Your code here

Need a hint?

Use while(1) for an infinite loop and toggle led_state inside the if.

3

Write an interrupt service routine (ISR) to toggle LED

Write a function called button_ISR with no parameters and void return type. Inside it, toggle led_state between 0 and 1 using led_state = 1 - led_state;. This simulates an interrupt toggling the LED immediately.

Embedded C

int button_state = 0;
int led_state = 0;

while(1) {
    if(button_state == 1) {
        led_state = 1 - led_state;
        button_state = 0;
    }
}

// Write ISR function button_ISR to toggle led_state
# Your code here

Need a hint?

Define button_ISR as a void function with no parameters and toggle led_state inside.

4

Print LED state changes to simulate output

Add printf statements inside the polling loop and inside button_ISR to print "LED is ON\n" when led_state is 1 and "LED is OFF\n" when led_state is 0. This shows the LED state changes.

Embedded C

int button_state = 0;
int led_state = 0;

while(1) {
    if(button_state == 1) {
        led_state = 1 - led_state;
        button_state = 0;
        // Print LED state here
    }
}

void button_ISR() {
    led_state = 1 - led_state;
    // Print LED state here
}

Need a hint?

Use a helper function to print LED state and call it after toggling led_state.