Resource manager task pattern in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a FreeRTOS task that manages a resource.

FreeRTOS

xTaskCreate([1], "ResourceManager", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY + 1, NULL);

Drag options to blanks, or click blank then click option'

AvTaskDelete

BvTaskStartScheduler

CxQueueCreate

DResourceManagerTask

Attempts:

3 left

💡 Hint

Common Mistakes

Using scheduler or queue functions instead of the task function name.

Passing NULL instead of the task function.

The function xTaskCreate needs the task function name as the first argument. Here, ResourceManagerTask is the task function that manages the resource.

2fill in blank

medium

Complete the code to wait for a resource request in the resource manager task.

FreeRTOS

if (xQueueReceive(resourceQueue, &request, [1]) == pdPASS) {
    // Process request
}

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A0

BpdFALSE

CportMAX_DELAY

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 which causes no wait and immediate return.

Using a small number which causes timeout.

Using portMAX_DELAY makes the task wait indefinitely until a request arrives in the queue.

3fill in blank

hard

Fix the error in the resource manager task to properly notify the requester after processing.

FreeRTOS

xTaskNotifyGive([1]);

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ArequestingTaskHandle

BNULL

CresourceQueue

DResourceManagerTaskHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing NULL or the queue handle instead of the task handle.

Not notifying the requester task.

The function xTaskNotifyGive must be called with the handle of the task that requested the resource, so it can be notified.

4fill in blank

hard

Fill both blanks to correctly send a resource request and wait for notification.

FreeRTOS

xQueueSend(resourceQueue, &request, [1]);
ulTaskNotifyTake([2], portMAX_DELAY);

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AportMAX_DELAY

BpdTRUE

CpdFALSE

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using portMAX_DELAY for queue send block time which can block indefinitely.

Using pdFALSE for ulTaskNotifyTake which does not clear the notification.

When sending to a queue, a zero block time means do not wait if the queue is full. For ulTaskNotifyTake, pdTRUE clears one bit from the notification value before checking or waiting.

5fill in blank

hard

Fill the blanks to implement a resource manager task loop that receives requests, processes them, and notifies the requester.

FreeRTOS

void ResourceManagerTask(void *pvParameters) {
    ResourceRequest request;
    for (;;) {
        if (xQueueReceive(resourceQueue, &request, [1]) == pdPASS) {
            // Process the request
            processResource(request.data);
            xTaskNotifyGive([2]);
        }
    }
}

Drag options to blanks, or click blank then click option'

AportMAX_DELAY

Brequest.taskHandle

CNULL

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong block time values.

Not notifying the correct task handle.

The task waits indefinitely for requests using portMAX_DELAY. After processing, it notifies the requesting task using request.taskHandle.

Practice

1. What is the main purpose of the Resource Manager Task Pattern in FreeRTOS?

easy

A. To centralize control of shared resources and prevent conflicts

B. To create multiple tasks accessing resources directly

C. To increase CPU usage by running more tasks simultaneously

D. To eliminate the need for task synchronization mechanisms

Solution

1. Step 1: Understand resource sharing challenges

   When multiple tasks access shared resources directly, conflicts and data corruption can occur.

2. Step 2: Role of Resource Manager Task

   The Resource Manager Task centralizes access, so tasks send requests to it instead of accessing resources directly, preventing conflicts.

3. Final Answer:

   To centralize control of shared resources and prevent conflicts -> Option A

4. Quick Check:

   Centralized control = Prevent conflicts [OK]

Hint: Resource manager centralizes resource access to avoid conflicts [OK]

Common Mistakes:

• Thinking tasks access resources directly
• Assuming it increases CPU usage
• Believing it removes synchronization needs

2. Which of the following is the correct way to send a request to a Resource Manager Task in FreeRTOS?

easy

A. Using a queue to send a request message to the manager task

B. Calling the resource manager function without synchronization

C. Directly accessing the shared resource variable

D. Using global variables without any task communication

Solution

1. Step 1: Identify communication method

   Resource Manager Tasks typically receive requests via queues to serialize access.

2. Step 2: Evaluate options

   Only Using a queue to send a request message to the manager task uses a queue to send requests, which is the correct and safe method.

3. Final Answer:

   Using a queue to send a request message to the manager task -> Option A

4. Quick Check:

   Queue communication = Correct request method [OK]

Hint: Use queues to send requests to resource manager task [OK]

Common Mistakes:

• Accessing shared variables directly
• Ignoring synchronization
• Using global variables without communication

3. Given the following FreeRTOS code snippet, what will be the output?

typedef struct {
  int command;
  int data;
} RequestMessage;

QueueHandle_t resourceQueue;

void ResourceManagerTask(void *params) {
  RequestMessage req;
  while (1) {
    if (xQueueReceive(resourceQueue, &req, portMAX_DELAY) == pdPASS) {
      if (req.command == 1) {
        printf("Processed data: %d\n", req.data * 2);
      }
    }
  }
}

void ClientTask(void *params) {
  RequestMessage msg = {1, 5};
  xQueueSend(resourceQueue, &msg, 0);
  vTaskDelete(NULL);
}

medium

A. Processed data: 5

B. Processed data: 10

C. No output, queue is empty

D. Runtime error due to invalid queue

Solution

1. Step 1: Analyze ClientTask sending message

   ClientTask sends a message with command=1 and data=5 to the resourceQueue.

2. Step 2: Analyze ResourceManagerTask processing

   ResourceManagerTask receives the message, checks command==1, then prints data*2 = 5*2 = 10.

3. Final Answer:

   Processed data: 10 -> Option B

4. Quick Check:

   Data 5 doubled = 10 output [OK]

Hint: Multiply data by 2 when command is 1 [OK]

Common Mistakes:

• Confusing data value with output
• Assuming no message received
• Ignoring the multiplication by 2

4. Identify the bug in this Resource Manager Task code snippet:

void ResourceManagerTask(void *params) {
  RequestMessage req;
  while (1) {
    if (xQueueReceive(resourceQueue, &req, 0) == pdPASS) {
      if (req.command == 1) {
        // Process command
      }
    }
  }
}

What is the problem?

medium

A. xQueueReceive should not be used in Resource Manager Task

B. RequestMessage struct is not defined

C. ResourceManagerTask should not use a while loop

D. Using zero block time causes missed messages if queue is empty

Solution

1. Step 1: Understand xQueueReceive block time

   Using 0 as block time means the call returns immediately if queue is empty, possibly missing messages.

2. Step 2: Effect on Resource Manager Task

   The task may spin without waiting, causing high CPU usage and missed processing.

3. Final Answer:

   Using zero block time causes missed messages if queue is empty -> Option D

4. Quick Check:

   Zero block time = possible missed messages [OK]

Hint: Use portMAX_DELAY to wait for messages in resource manager [OK]

Common Mistakes:

• Ignoring block time effect
• Thinking struct is undefined
• Believing while loop is wrong

5. You want to design a Resource Manager Task that handles multiple resource types (e.g., UART, SPI) with different commands. Which approach best applies the Resource Manager Task Pattern to handle this efficiently?

hard

A. Create separate manager tasks for each resource type and let clients send requests directly to each

B. Let clients access resources directly with mutexes protecting each resource

C. Use a single queue with a message struct containing resource type and command fields, then switch-case inside the manager task

D. Use global variables to store resource states and update them without task communication

Solution

1. Step 1: Consider centralized control for multiple resources

   A single Resource Manager Task can handle multiple resource types by differentiating requests.

2. Step 2: Use message struct with resource type and command

   This allows the manager task to use a switch-case to process requests efficiently and safely.

3. Final Answer:

   Use a single queue with a message struct containing resource type and command fields, then switch-case inside the manager task -> Option C

4. Quick Check:

   Single queue + message struct = efficient multi-resource management [OK]

Hint: Use message struct with resource type and switch-case in manager [OK]

Common Mistakes:

• Creating multiple manager tasks unnecessarily
• Allowing direct resource access with mutexes
• Using global variables without communication