Nested interrupts in Embedded C - Mini Project: Build & Apply

Nested Interrupts in Embedded C

📖 Scenario: You are working on a simple embedded system that handles two types of interrupts: a timer interrupt and an external button interrupt. The system should allow the button interrupt to interrupt the timer interrupt handler, demonstrating nested interrupts.

🎯 Goal: Build a program in Embedded C that sets up two interrupt service routines (ISRs) with nested interrupts enabled. The timer ISR will increment a counter, and the button ISR will increment a separate counter. The button ISR should be able to interrupt the timer ISR.

📋 What You'll Learn

Create two counters: timer_count and button_count initialized to 0

Create a configuration variable nested_interrupts_enabled set to 1 to enable nested interrupts

Write two ISR functions: Timer_ISR() and Button_ISR()

In Timer_ISR(), increment timer_count and simulate enabling nested interrupts

In Button_ISR(), increment button_count

Simulate calling Timer_ISR() and inside it call Button_ISR() to show nesting

Print the final values of timer_count and button_count

💡 Why This Matters

🌍 Real World

Embedded systems often need to handle multiple interrupts where higher priority interrupts can interrupt lower priority ones. This project shows how nested interrupts work in a simple way.

💼 Career

Understanding nested interrupts is important for embedded software engineers working on microcontrollers, real-time systems, and hardware interfacing.

1

Create counters for interrupts

Create two integer variables called timer_count and button_count and set both to 0.

Embedded C

// Create two integer counters timer_count and button_count and set them to 0
// Your code here

Need a hint?

Use int to declare the counters and set them to zero.

2

Enable nested interrupts configuration

Create an integer variable called nested_interrupts_enabled and set it to 1 to represent that nested interrupts are enabled.

Embedded C

int timer_count = 0;
int button_count = 0;

// Create nested_interrupts_enabled variable and set it to 1
// Your code here

Need a hint?

This variable will simulate enabling nested interrupts.

3

Write the interrupt service routines

Write two functions: void Timer_ISR() and void Button_ISR(). In Timer_ISR(), increment timer_count. If nested_interrupts_enabled is 1, call Button_ISR() inside Timer_ISR(). In Button_ISR(), increment button_count.

Embedded C

int timer_count = 0;
int button_count = 0;

int nested_interrupts_enabled = 1;

// Write Timer_ISR and Button_ISR functions
// Your code here

Need a hint?

Define the two functions and use the nested_interrupts_enabled variable to decide when to call Button_ISR() inside Timer_ISR().

4

Simulate interrupts and print results

Call Timer_ISR() once to simulate the timer interrupt. Then print the values of timer_count and button_count using printf in the format: "Timer count: %d\nButton count: %d\n".

Embedded C

int timer_count = 0;
int button_count = 0;

int nested_interrupts_enabled = 1;

void Button_ISR() {
    button_count++;
}

void Timer_ISR() {
    timer_count++;
    if (nested_interrupts_enabled == 1) {
        Button_ISR();
    }
}

// Call Timer_ISR and print the counts
// Your code here

Need a hint?

Call Timer_ISR() once and then use printf to show the counts.