configMAX_SYSCALL_INTERRUPT_PRIORITY in FreeRTOS - Mini Project: Build & Apply

Understanding configMAX_SYSCALL_INTERRUPT_PRIORITY in FreeRTOS

📖 Scenario: You are working on a FreeRTOS-based embedded system. You need to configure interrupt priorities correctly to ensure that FreeRTOS API functions are called safely from interrupts.

🎯 Goal: Learn how to set configMAX_SYSCALL_INTERRUPT_PRIORITY and use it to protect critical sections in interrupt handlers.

📋 What You'll Learn

Create a macro configMAX_SYSCALL_INTERRUPT_PRIORITY with the value 5

Create a variable current_priority to simulate the current interrupt priority

Write a function can_call_freertos_api() that returns 1 if current_priority is equal or higher (numerically greater or equal) than configMAX_SYSCALL_INTERRUPT_PRIORITY, else 0

Print the result of can_call_freertos_api() for current_priority values 3 and 6

💡 Why This Matters

🌍 Real World

In embedded systems, setting <code>configMAX_SYSCALL_INTERRUPT_PRIORITY</code> correctly ensures that interrupts with higher priority do not call FreeRTOS API functions, preventing system crashes.

💼 Career

Embedded software engineers must configure interrupt priorities properly to write safe and reliable real-time applications using FreeRTOS.

1

Define configMAX_SYSCALL_INTERRUPT_PRIORITY

Define a macro called configMAX_SYSCALL_INTERRUPT_PRIORITY and set it to 5.

FreeRTOS

# Define configMAX_SYSCALL_INTERRUPT_PRIORITY as 5
# Your code here

Need a hint?

This macro sets the highest interrupt priority from which FreeRTOS API calls can be made.

2

Create current_priority variable

Create an integer variable called current_priority and set it to 0.

FreeRTOS

#define configMAX_SYSCALL_INTERRUPT_PRIORITY 5

// Create current_priority variable and set to 0
# Your code here

Need a hint?

This variable will simulate the priority of the current interrupt.

3

Write can_call_freertos_api() function

Write a function called can_call_freertos_api() that returns 1 if current_priority is greater than or equal to configMAX_SYSCALL_INTERRUPT_PRIORITY, otherwise returns 0.

FreeRTOS

#define configMAX_SYSCALL_INTERRUPT_PRIORITY 5

int current_priority = 0;

// Write can_call_freertos_api() function below
# Your code here

Need a hint?

Use a simple if-else to compare current_priority with configMAX_SYSCALL_INTERRUPT_PRIORITY.

4

Test can_call_freertos_api() with different priorities

Set current_priority to 3 and print the result of can_call_freertos_api(). Then set current_priority to 6 and print the result again.

FreeRTOS

#define configMAX_SYSCALL_INTERRUPT_PRIORITY 5

int current_priority = 0;

int can_call_freertos_api() {
    if (current_priority >= configMAX_SYSCALL_INTERRUPT_PRIORITY) {
        return 1;
    } else {
        return 0;
    }
}

// Set current_priority to 3 and print can_call_freertos_api()
// Set current_priority to 6 and print can_call_freertos_api()
# Your code here

Need a hint?

Remember to include stdio.h and use printf to show the results.