Critical sections and interrupt disabling in FreeRTOS - Mini Project: Build & Apply

Critical Sections and Interrupt Disabling in FreeRTOS

📖 Scenario: You are working on a small embedded system using FreeRTOS. You need to protect a shared variable from being changed by an interrupt while your task is updating it. This is important to avoid errors caused by simultaneous access.

🎯 Goal: Build a simple FreeRTOS program that safely updates a shared variable by disabling interrupts during the update, demonstrating the use of critical sections.

📋 What You'll Learn

Create a shared variable called sharedCounter initialized to 0

Create a variable called interruptMask to hold the interrupt state

Use taskENTER_CRITICAL() and taskEXIT_CRITICAL() to protect the update of sharedCounter

Print the value of sharedCounter after the update

💡 Why This Matters

🌍 Real World

Embedded systems often have tasks and interrupts accessing the same data. Protecting shared data with critical sections prevents errors and crashes.

💼 Career

Understanding how to disable interrupts and use critical sections is essential for embedded software engineers working with real-time operating systems like FreeRTOS.

1

Create the shared variable

Create a global variable called sharedCounter and set it to 0.

FreeRTOS

# Create a global variable called sharedCounter and set it to 0
# Your code here

Need a hint?

Use volatile to tell the compiler this variable can change unexpectedly.

2

Create the interrupt mask variable

Create a variable called interruptMask of type UBaseType_t to hold the interrupt state before disabling interrupts.

FreeRTOS

volatile int sharedCounter = 0;
// Create a variable called interruptMask of type UBaseType_t
// Your code here

Need a hint?

This variable will store the interrupt state returned by taskENTER_CRITICAL_FROM_ISR().

3

Protect the update with critical section

Use taskENTER_CRITICAL() and taskEXIT_CRITICAL() to disable interrupts while increasing sharedCounter by 1. Use taskENTER_CRITICAL() and taskEXIT_CRITICAL() to protect the update.

FreeRTOS

volatile int sharedCounter = 0;
UBaseType_t interruptMask;

// Disable interrupts and increase sharedCounter by 1 safely
// Your code here

Need a hint?

Wrap the update inside the critical section calls to prevent interrupts during the change.

4

Print the updated value

Print the value of sharedCounter using printf to show the result after the critical section update.

FreeRTOS

volatile int sharedCounter = 0;
UBaseType_t interruptMask;

taskENTER_CRITICAL();
sharedCounter += 1;
taskEXIT_CRITICAL();

// Print the value of sharedCounter
// Your code here

Need a hint?

Use printf with the format specifier %d to print the integer value.