xTaskNotify() with value in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to notify a task with a value using xTaskNotify.

FreeRTOS

xTaskNotify([1], 0x01, eSetValueWithOverwrite);

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

ANULL

BvTaskDelay

CxTaskHandle

DxTaskNotify

Attempts:

3 left

💡 Hint

Common Mistakes

Passing NULL instead of the task handle.

Using a function name instead of a task handle.

The first argument to xTaskNotify is the handle of the task to notify.

2fill in blank

medium

Complete the code to notify a task with the value 0x10 using xTaskNotify.

FreeRTOS

xTaskNotify(xTaskHandle, [1], eSetValueWithOverwrite);

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

A0x10

B0x00

C1

D0xFF

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0x10.

Using 0xFF which is a different value.

The second argument is the notification value to send, here 0x10.

3fill in blank

hard

Fix the error in the code to notify a task with a value using xTaskNotify.

FreeRTOS

xTaskNotify(xTaskHandle, 0x05, [1]);

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

AeSetBits

BeSetValueWithOverwrite

CeNoAction

DeIncrement

Attempts:

3 left

💡 Hint

Common Mistakes

Using eNoAction which does not set a value.

Using eSetBits which sets bits instead of value.

The third argument must be a valid notification action. eSetValueWithOverwrite sets the notification value directly.

4fill in blank

hard

Fill both blanks to notify a task with value 0x0F using xTaskNotify and the correct notification action.

FreeRTOS

xTaskNotify([1], [2], eSetValueWithOverwrite);

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

AxTaskHandle

B0x0F

C0xF0

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL instead of the task handle.

Using 0xF0 instead of 0x0F.

The first blank is the task handle, the second is the notification value 0x0F.

5fill in blank

hard

Fill all three blanks to notify a task with value 0xAA using xTaskNotify.

FreeRTOS

xTaskNotify([1], [2], [3]);

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

AxTaskHandle

B0xAA

CeSetValueWithOverwrite

DeNoAction

Attempts:

3 left

💡 Hint

Common Mistakes

Using eNoAction which does nothing.

Wrong value or action.

Incorrect argument order.

The first argument is the task handle, second is the value 0xAA, third is the notification action eSetValueWithOverwrite.

Practice

1.

What does the xTaskNotify() function primarily do in FreeRTOS?

easy

A. Creates a new task in the system

B. Deletes a task from the scheduler

C. Sends a notification value from one task to another

D. Suspends the current task indefinitely

Solution

1. Step 1: Understand the purpose of xTaskNotify()

   The function is designed to send a notification value or signal from one task to another in FreeRTOS.

2. Step 2: Compare with other task functions

   Creating, deleting, or suspending tasks are done by other FreeRTOS functions, not xTaskNotify().

3. Final Answer:

   Sends a notification value from one task to another -> Option C

4. Quick Check:

   xTaskNotify() sends notification value [OK]

Hint: Remember: xTaskNotify() sends signals between tasks [OK]

Common Mistakes:

• Confusing xTaskNotify() with task creation functions
• Thinking it suspends or deletes tasks
• Assuming it handles task priorities

2.

Which of the following is the correct syntax to send a notification with a value using xTaskNotify()?

BaseType_t xTaskNotify( TaskHandle_t xTaskToNotify, uint32_t ulValue, eNotifyAction eAction );

easy

A. xTaskNotify(taskHandle, 10, eSetBits);

B. xTaskNotify(10, taskHandle, eSetValueWithOverwrite);

C. xTaskNotify(taskHandle, eSetValueWithoutOverwrite, 10);

D. xTaskNotify(eSetValueWithOverwrite, taskHandle, 10);

Solution

1. Step 1: Identify parameter order in xTaskNotify()

   The correct order is: TaskHandle_t, uint32_t value, eNotifyAction.

2. Step 2: Match options to correct order

   xTaskNotify(taskHandle, 10, eSetBits); matches the correct order: taskHandle, 10, eSetBits. Others mix parameter order incorrectly.

3. Final Answer:

   xTaskNotify(taskHandle, 10, eSetBits); -> Option A

4. Quick Check:

   Correct parameter order: task, value, action [OK]

Hint: Remember parameter order: task, value, action [OK]

Common Mistakes:

• Swapping value and task handle parameters
• Using wrong enum for eNotifyAction
• Passing parameters in wrong order

3.

Consider the following code snippet:

uint32_t notifiedValue = 0;

// Task A sends notification
xTaskNotify(taskBHandle, 0x04, eSetBits);

// Task B waits for notification
xTaskNotifyWait(0x00, 0xFFFFFFFF, ¬ifiedValue, portMAX_DELAY);

// What is the value of notifiedValue after notification?

medium

A. 0x04

B. 0x00

C. 0xFFFFFFFF

D. Undefined

Solution

1. Step 1: Understand eSetBits action

   eSetBits sets bits in the notification value. Since initial is 0, setting bit 0x04 results in notifiedValue = 0x04.

2. Step 2: Check xTaskNotifyWait parameters

   It clears bits 0x00 (none) and waits indefinitely, storing the notified bits in notifiedValue.

3. Final Answer:

   0x04 -> Option A

4. Quick Check:

   eSetBits sets bits = 0x04 [OK]

Hint: eSetBits adds bits to notified value [OK]

Common Mistakes:

• Assuming notifiedValue remains zero
• Confusing eSetBits with eSetValueWithoutOverwrite
• Ignoring the effect of xTaskNotifyWait

4.

Identify the error in the following code snippet using xTaskNotify():

BaseType_t status;
status = xTaskNotify(NULL, 5, eSetValueWithOverwrite);
if(status == pdPASS) {
    // Notification sent
}

medium

A. Missing return statement in function

B. Using eSetValueWithOverwrite is invalid

C. Notification value must be zero

D. Passing NULL as task handle causes error

Solution

1. Step 1: Check task handle parameter

   xTaskNotify requires a valid task handle; NULL is invalid and causes failure.

2. Step 2: Validate other parameters

   eSetValueWithOverwrite and value 5 are valid; no return statement needed here.

3. Final Answer:

   Passing NULL as task handle causes error -> Option D

4. Quick Check:

   Task handle NULL invalid [OK]

Hint: Task handle must never be NULL [OK]

Common Mistakes:

• Passing NULL as task handle
• Thinking notification value must be zero
• Confusing eNotifyAction enums

5.

You want to send a notification value from Task A to Task B, but only if Task B's current notification value is zero. Which eNotifyAction should you use with xTaskNotify() to achieve this?

hard

A. eSetValueWithOverwrite

B. eSetValueWithoutOverwrite

C. eIncrement

D. eNoAction

Solution

1. Step 1: Understand eNotifyAction options

   eSetValueWithoutOverwrite sets the notification value only if it is currently zero.

2. Step 2: Compare with other actions

   eSetValueWithOverwrite always overwrites; eIncrement adds 1; eNoAction sends no value.

3. Final Answer:

   eSetValueWithoutOverwrite -> Option B

4. Quick Check:

   Set only if zero = eSetValueWithoutOverwrite [OK]

Hint: Use eSetValueWithoutOverwrite to avoid overwriting [OK]

Common Mistakes:

• Using eSetValueWithOverwrite and overwriting value
• Choosing eIncrement which changes value incorrectly
• Selecting eNoAction which sends no value