Resource manager task pattern in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this FreeRTOS resource manager task code?

Consider a FreeRTOS task that manages access to a shared resource using a queue. What will be printed when the task receives a request?

FreeRTOS

#include "FreeRTOS.h"
#include "task.h"
#include "queue.h"
#include <stdio.h>

QueueHandle_t resourceQueue;

void ResourceManagerTask(void *pvParameters) {
    char *request;
    while(1) {
        if(xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS) {
            printf("Processing request: %s\n", request);
            vTaskDelay(pdMS_TO_TICKS(100));
        }
    }
}

int main() {
    resourceQueue = xQueueCreate(5, sizeof(char*));
    xTaskCreate(ResourceManagerTask, "ResMgr", 1000, NULL, 1, NULL);
    char *req = "Task1 Request";
    xQueueSend(resourceQueue, &req, 0);
    vTaskStartScheduler();
    return 0;
}

A Processing request: Task1 Request

B Processing request: (null)

C Compilation error due to missing queue initialization

D Runtime error: Queue handle is NULL

💡 Hint

Check how the queue is created and how the request is sent and received.

The queue is created properly before the task starts. The request string pointer is sent to the queue and received correctly, so the task prints the request string.

🧠 Conceptual

intermediate

Which synchronization primitive is best for a FreeRTOS resource manager task to protect a shared resource?

In a FreeRTOS resource manager task pattern, which synchronization method ensures exclusive access to a shared resource?

A Binary semaphore

B Mutex

C Counting semaphore

D Event group

💡 Hint

Think about priority inheritance and exclusive access.

A mutex is designed to provide exclusive access and supports priority inheritance, preventing priority inversion in FreeRTOS.

🔧 Debug

advanced

What error does this FreeRTOS resource manager task code produce?

Analyze the code below. What error will occur when running this resource manager task?

FreeRTOS

QueueHandle_t resourceQueue;

void ResourceManagerTask(void *pvParameters) {
    char request[20];
    while(1) {
        if(xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS) {
            printf("Request: %s\n", request);
        }
    }
}

int main() {
    resourceQueue = xQueueCreate(5, sizeof(char*));
    xTaskCreate(ResourceManagerTask, "ResMgr", 1000, NULL, 1, NULL);
    char req[] = "Request1";
    xQueueSend(resourceQueue, &req, 0);
    vTaskStartScheduler();
    return 0;
}

A Incorrect output: prints garbage instead of request string

B No error, prints 'Request1' correctly

C Compilation error: incompatible pointer types

D Runtime error: Stack overflow in ResourceManagerTask

💡 Hint

Check the queue item size and what is sent/received.

The queue is created to hold pointers (char*), but the task receives into a char array. This mismatch causes the task to print garbage because the pointer is interpreted as data.

📝 Syntax

advanced

Which option fixes the syntax error in this FreeRTOS resource manager task snippet?

Identify the correct fix for the syntax error in the following snippet:

if xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS {
    processRequest(request);
}

A

if (xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS) then {
    processRequest(request);
}

B

if xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS then {
    processRequest(request);
}

C

if xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS:
    processRequest(request);

D

if (xQueueReceive(resourceQueue, &request, portMAX_DELAY) == pdPASS) {
    processRequest(request);
}

💡 Hint

Remember C syntax for if statements.

In C, the condition must be inside parentheses and the block inside braces without 'then'.

🚀 Application

expert

How many items can the FreeRTOS resource manager queue hold in this configuration?

Given the queue creation below, how many items can it hold?

resourceQueue = xQueueCreate(10, sizeof(int));

A Cannot hold any items because size is incorrect

B 1 item, size 10 * sizeof(int)

C 10 items, each of size int

D Depends on the FreeRTOS heap size only

💡 Hint

Check the parameters of xQueueCreate.

The first parameter is the number of items, the second is the size of each item. So the queue holds 10 items of int size.