Tick timer and scheduler in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Tick Count Increment Behavior

What will be the output of the following FreeRTOS tick count code snippet after 3 ticks?

FreeRTOS

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

TickType_t tickCount = 0;

void vApplicationTickHook(void) {
    tickCount = xTaskGetTickCount();
}

int main() {
    // Simulate 3 ticks
    for (int i = 0; i < 3; i++) {
        vApplicationTickHook();
    }
    printf("Tick count: %u\n", (unsigned int)tickCount);
    return 0;
}

A Tick count: 1

B Tick count: 3

C Tick count: 0

D Tick count: 2

💡 Hint

Observe that the scheduler is not started in the code, so xTaskGetTickCount() returns 0.

The code attempts to simulate 3 ticks by calling vApplicationTickHook() in a loop. However, since vTaskStartScheduler() is never called, the FreeRTOS scheduler and tick interrupt are not running. Therefore, xTaskGetTickCount() always returns 0, and the output is 'Tick count: 0'.

🧠 Conceptual

intermediate

Role of the Tick Timer in FreeRTOS

What is the primary role of the tick timer in FreeRTOS?

A To provide a periodic interrupt that drives the scheduler and time-related functions

B To handle all hardware interrupts in the system

C To manage memory allocation for tasks

D To initialize the CPU clock frequency

💡 Hint

Think about what triggers task switching and delays.

The tick timer generates periodic interrupts that allow the scheduler to switch tasks and manage delays/timeouts.

🔧 Debug

advanced

Why Does the Scheduler Not Switch Tasks?

Given the following FreeRTOS configuration snippet, why does the scheduler never switch tasks?

#define configUSE_PREEMPTION 0
#define configTICK_RATE_HZ 1000

void vTask1(void *pvParameters) {
    while(1) {
        // Task code
    }
}

void vTask2(void *pvParameters) {
    while(1) {
        // Task code
    }
}

int main() {
    xTaskCreate(vTask1, "Task1", 1000, NULL, 1, NULL);
    xTaskCreate(vTask2, "Task2", 1000, NULL, 1, NULL);
    vTaskStartScheduler();
    return 0;
}

A Because preemption is disabled, so tasks only switch on yield or blocking calls

B Because the tick rate is too high causing scheduler overload

C Because tasks have the same priority and scheduler cannot decide

D Because tasks are missing calls to vTaskDelay()

💡 Hint

Check the configUSE_PREEMPTION setting.

With preemption disabled, the scheduler switches tasks only when tasks yield or block. Without explicit yield, the first task runs forever.

📝 Syntax

advanced

Identify the Syntax Error in Tick Hook Implementation

Which option contains the correct syntax for implementing the FreeRTOS tick hook function?

A void vApplicationTickHook() { /* user code */ }

B void vApplicationTickHook(void) { /* user code */ }

C void vApplicationTickHook(void) -> void { /* user code */ }

D void vApplicationTickHook(void); { /* user code */ }

💡 Hint

Check the correct C function declaration syntax.

Option B correctly declares the tick hook function with void parameter and no return value.

🚀 Application

expert

Calculating Tick Overflow Time

Given a FreeRTOS tick rate of 1000 Hz and a 32-bit tick counter, how long in days will it take for the tick count to overflow?

A Approximately 24 hours

B Approximately 365 days

C Approximately 100 days

D Approximately 49.7 days

💡 Hint

Calculate total ticks before overflow and convert to time.

The 32-bit counter max value is 2^32 - 1 ticks. At 1000 ticks per second, overflow time = (2^32 / 1000) seconds ≈ 4294967 seconds ≈ 49.7 days.