uxTaskPriorityGet() for reading priority in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of uxTaskPriorityGet() for a created task?

Consider the following FreeRTOS code snippet. What will be the output printed by printf?

FreeRTOS

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

void vTaskFunction(void *pvParameters) {
    // Task code here
    vTaskDelete(NULL);
}

int main() {
    TaskHandle_t xTaskHandle = NULL;
    BaseType_t xReturned;
    UBaseType_t uxPriority;

    xReturned = xTaskCreate(vTaskFunction, "Task1", configMINIMAL_STACK_SIZE, NULL, 3, &xTaskHandle);
    if(xReturned == pdPASS) {
        uxPriority = uxTaskPriorityGet(xTaskHandle);
        printf("Task priority: %u\n", (unsigned int)uxPriority);
    }
    return 0;
}

A Task priority: 3

B Task priority: 0

C Compilation error due to missing task handle

D Task priority: configMAX_PRIORITIES

💡 Hint

Remember that uxTaskPriorityGet() returns the priority assigned when the task was created.

The task was created with priority 3, so uxTaskPriorityGet() returns 3. Option A is wrong because 0 is the idle priority. Option A is wrong because configMAX_PRIORITIES is the max allowed, not assigned. Option A is wrong because the task handle is correctly passed.

🧠 Conceptual

intermediate

What does uxTaskPriorityGet() return if passed NULL?

In FreeRTOS, what is the return value of uxTaskPriorityGet(NULL) when called from within a task?

A The priority of the calling task

B Zero (lowest priority)

C configMAX_PRIORITIES

D Causes a runtime error

💡 Hint

Passing NULL means the function uses the current task handle internally.

When uxTaskPriorityGet() is called with NULL, it returns the priority of the task that called the function. It does not cause an error or return zero.

🔧 Debug

advanced

Why does uxTaskPriorityGet() return 0 unexpectedly?

A developer creates a task with priority 4 but uxTaskPriorityGet() returns 0 for that task's handle. What is the most likely cause?

A The FreeRTOS kernel is not started yet

B The task priority was set to 0 after creation

C The task handle passed to <code>uxTaskPriorityGet()</code> is invalid or uninitialized

D The task was deleted before calling <code>uxTaskPriorityGet()</code>

💡 Hint

Check if the task handle is properly assigned after task creation.

If the task handle is invalid or NULL, uxTaskPriorityGet() may return 0 because it cannot find the task's priority. Other options are less likely because priority 0 means idle, and kernel not started or deleted task would cause different behaviors.

📝 Syntax

advanced

Which code snippet correctly reads a task's priority?

Which of the following code snippets correctly uses uxTaskPriorityGet() to read the priority of a task?

A UBaseType_t prio = uxTaskPriorityGet(&xTaskHandle);

B UBaseType_t prio = uxTaskPriorityGet(xTaskHandle);

C int prio = uxTaskPriorityGet(xTaskHandle);

D UBaseType_t prio = uxTaskPriorityGet(NULL, xTaskHandle);

💡 Hint

Check the function signature and parameter types.

uxTaskPriorityGet() takes a TaskHandle_t (not a pointer to it) and returns UBaseType_t. Option B matches this. Option B uses wrong return type. Option B passes pointer incorrectly. Option B passes two parameters which is invalid.

🚀 Application

expert

How to check and print the priority of the current task safely?

Write the correct sequence of code lines to get and print the priority of the currently running task in FreeRTOS.

A 3,4,1,2,5

B 3,1,4,2,5

C 1,3,2,4,5

D 1,2,3,4,5

💡 Hint

Declare variables first, then get current task handle, then get priority, then print.

The correct order is to declare variables (1,2), get current task handle (3), get priority (4), then print (5). Options that get handle before declaring variables or mix order are invalid.

Practice

1.

What does the FreeRTOS function uxTaskPriorityGet() do?

easy

A. It returns the priority of a specified task.

B. It sets the priority of a specified task.

C. It deletes a specified task.

D. It creates a new task.

Solution

1. Step 1: Understand the function purpose

   uxTaskPriorityGet() is designed to read the priority of a task, not to modify or manage tasks.

2. Step 2: Match function behavior to options

   Only "It returns the priority of a specified task." correctly states it returns the priority of a specified task.

3. Final Answer:

   It returns the priority of a specified task. -> Option A

4. Quick Check:

   uxTaskPriorityGet() reads priority = It returns the priority of a specified task. [OK]

Hint: Remember: 'Get' means read, not change [OK]

Common Mistakes:

• Confusing 'get' with 'set' functions
• Thinking it creates or deletes tasks
• Assuming it returns task handle

2.

Which of the following is the correct way to get the priority of the current task using uxTaskPriorityGet()?

TaskHandle_t xTaskHandle;
UBaseType_t uxPriority = ?;

easy

A. uxPriority = uxTaskPriorityGet(xTaskHandle);

B. uxPriority = uxTaskPriorityGet(NULL);

C. uxPriority = uxTaskPriorityGet(&xTaskHandle);

D. uxPriority = uxTaskPriorityGet(*xTaskHandle);

Solution

1. Step 1: Recall how to get current task priority

   Passing NULL to uxTaskPriorityGet() returns the priority of the current task.

2. Step 2: Check each option

   uxPriority = uxTaskPriorityGet(xTaskHandle); uses uninitialized xTaskHandle (undefined behavior). uxPriority = uxTaskPriorityGet(&xTaskHandle); passes address (wrong type). uxPriority = uxTaskPriorityGet(*xTaskHandle); dereferences uninitialized handle (crash). Only uxPriority = uxTaskPriorityGet(NULL); is correct.

3. Final Answer:

   uxPriority = uxTaskPriorityGet(NULL); -> Option B

4. Quick Check:

   Use NULL for current task priority [OK]

Hint: Pass NULL to get current task priority [OK]

Common Mistakes:

• Passing address of handle instead of handle
• Dereferencing handle incorrectly
• Using uninitialized task handle

3.

Given the following code snippet, what will be printed?

TaskHandle_t xHandle = xTaskGetHandle("Task1");
UBaseType_t uxPriority = uxTaskPriorityGet(xHandle);
printf("Priority: %u\n", uxPriority);

Assume "Task1" exists and has priority 3.

medium

A. Priority: 0

B. Compilation error

C. Priority: 3

D. Priority: 1

Solution

1. Step 1: Understand task handle retrieval

   xTaskGetHandle("Task1") returns the handle of the task named "Task1" which exists with priority 3.

2. Step 2: Use uxTaskPriorityGet() to read priority

   Calling uxTaskPriorityGet(xHandle) returns the priority of that task, which is 3.

3. Final Answer:

   Priority: 3 -> Option C

4. Quick Check:

   uxTaskPriorityGet returns task priority = 3 [OK]

Hint: Get handle then get priority returns actual task priority [OK]

Common Mistakes:

• Assuming default priority 0
• Confusing handle with task name
• Expecting syntax error

4.

Identify the error in this code snippet:

TaskHandle_t xHandle;
UBaseType_t uxPriority = uxTaskPriorityGet(xHandle);
printf("Priority: %u\n", uxPriority);

medium

A. xHandle is uninitialized before use.

B. uxTaskPriorityGet() cannot be called with a TaskHandle_t.

C. printf format specifier is incorrect.

D. uxPriority should be a pointer.

Solution

1. Step 1: Check variable initialization

   xHandle is declared but not assigned any value before use.

2. Step 2: Understand consequences of uninitialized handle

   Passing an uninitialized handle to uxTaskPriorityGet() leads to undefined behavior or incorrect priority reading.

3. Final Answer:

   xHandle is uninitialized before use. -> Option A

4. Quick Check:

   Always initialize task handles before use [OK]

Hint: Initialize task handle before getting priority [OK]

Common Mistakes:

• Ignoring uninitialized variables
• Misunderstanding function parameter types
• Assuming pointer needed for uxPriority

5.

You want to check if the current task has higher priority than another task named "WorkerTask". Which code snippet correctly compares their priorities?

TaskHandle_t xWorkerHandle = xTaskGetHandle("WorkerTask");
UBaseType_t uxCurrentPriority = uxTaskPriorityGet(NULL);
UBaseType_t uxWorkerPriority = uxTaskPriorityGet(xWorkerHandle);
// What next?

hard

A. if (uxCurrentPriority != uxWorkerPriority) { /* current task higher */ }

B. if (uxCurrentPriority < uxWorkerPriority) { /* current task higher */ }

C. if (uxCurrentPriority == uxWorkerPriority) { /* current task higher */ }

D. if (uxCurrentPriority > uxWorkerPriority) { /* current task higher */ }

Solution

1. Step 1: Understand priority comparison logic

   Higher numeric value means higher priority in FreeRTOS.

2. Step 2: Compare current and worker task priorities

   Use > operator to check if current task priority is higher than worker's.

3. Final Answer:

   if (uxCurrentPriority > uxWorkerPriority) { /* current task higher */ } -> Option D

4. Quick Check:

   Higher number = higher priority [OK]

Hint: Use '>' to check if current task priority is higher [OK]

Common Mistakes:

• Using '<' instead of '>' for priority comparison
• Confusing equality with higher priority
• Not retrieving correct task handles