Event-driven architecture in FreeRTOS - Mini Project: Build & Apply

Event-driven Architecture with FreeRTOS

📖 Scenario: You are building a simple embedded system using FreeRTOS. The system should respond to button presses by sending events to a task that processes them. This simulates how event-driven architecture works in real devices.

🎯 Goal: Create a FreeRTOS program that uses an event queue to handle button press events. You will set up the event queue, send events from an interrupt handler, and process them in a task.

📋 What You'll Learn

Create an event queue called eventQueue with space for 5 events

Define an event type ButtonEvent as an integer

Create a task called EventProcessorTask that waits for events from eventQueue

Simulate sending a button press event with value 1 to eventQueue

Print the received event value inside EventProcessorTask

💡 Why This Matters

🌍 Real World

Event-driven architecture is common in embedded systems where tasks react to hardware events like button presses or sensor signals.

💼 Career

Understanding event queues and task communication is essential for embedded software developers working with real-time operating systems like FreeRTOS.

1

Setup Event Queue and Event Type

Create a FreeRTOS queue called eventQueue that can hold 5 integers. Define a type ButtonEvent as int.

FreeRTOS

// Your code here
// Create eventQueue and define ButtonEvent type

Need a hint?

Use xQueueCreate to make the queue. The queue holds 5 items of type ButtonEvent.

2

Create Event Processor Task

Write a FreeRTOS task function called EventProcessorTask that waits indefinitely to receive a ButtonEvent from eventQueue. Inside the task, declare a variable event of type ButtonEvent to receive the event.

FreeRTOS

#include "FreeRTOS.h"
#include "queue.h"

typedef int ButtonEvent;
QueueHandle_t eventQueue;

void setup() {
    eventQueue = xQueueCreate(5, sizeof(ButtonEvent));
}

// Write EventProcessorTask function below
// Your code here

Need a hint?

Use xQueueReceive with portMAX_DELAY to wait forever for an event.

3

Send Button Press Event

Inside the setup function, send a button press event with value 1 to eventQueue using xQueueSend.

FreeRTOS

#include "FreeRTOS.h"
#include "queue.h"
#include "task.h"
#include 

typedef int ButtonEvent;
QueueHandle_t eventQueue;

void setup() {
    eventQueue = xQueueCreate(5, sizeof(ButtonEvent));
    // Send button press event with value 1
    // Your code here
}

void EventProcessorTask(void *pvParameters) {
    ButtonEvent event;
    for (;;) {
        if (xQueueReceive(eventQueue, &event, portMAX_DELAY) == pdPASS) {
            printf("Received event: %d\n", event);
        }
    }
}

Need a hint?

Create a variable pressEvent with value 1 and send it to eventQueue with zero wait time.

4

Print Event in Task

Add a main function that calls setup(), creates the EventProcessorTask with priority 1, and starts the FreeRTOS scheduler. The program should print Received event: 1 when the event is processed.

FreeRTOS

#include "FreeRTOS.h"
#include "queue.h"
#include "task.h"
#include 

typedef int ButtonEvent;
QueueHandle_t eventQueue;

void setup() {
    eventQueue = xQueueCreate(5, sizeof(ButtonEvent));
    ButtonEvent pressEvent = 1;
    xQueueSend(eventQueue, &pressEvent, 0);
}

void EventProcessorTask(void *pvParameters) {
    ButtonEvent event;
    for (;;) {
        if (xQueueReceive(eventQueue, &event, portMAX_DELAY) == pdPASS) {
            printf("Received event: %d\n", event);
        }
    }
}

// Add main function below
// Your code here

Need a hint?

Use xTaskCreate to create the task and vTaskStartScheduler() to start FreeRTOS. The program prints the event when received.