vTaskDelayUntil() for precise timing in FreeRTOS - Mini Project: Build & Apply

Using vTaskDelayUntil() for Precise Timing in FreeRTOS

📖 Scenario: You are programming a FreeRTOS task that needs to toggle an LED at a precise 500 ms interval. Using vTaskDelayUntil() helps keep the timing exact, even if the task takes some time to run.

🎯 Goal: Create a FreeRTOS task that toggles an LED every 500 milliseconds using vTaskDelayUntil() for precise timing.

📋 What You'll Learn

Create a variable to hold the last wake time using TickType_t

Set a delay interval of 500 milliseconds using pdMS_TO_TICKS(500)

Use vTaskDelayUntil() inside the task loop to wait precisely

Toggle the LED inside the loop

Print a message each time the LED toggles

💡 Why This Matters

🌍 Real World

Precise timing is important in embedded systems for tasks like blinking LEDs, reading sensors, or controlling motors at exact intervals.

💼 Career

Understanding <code>vTaskDelayUntil()</code> is essential for embedded developers working with FreeRTOS to create reliable and predictable real-time applications.

1

Create the task function and last wake time variable

Write a FreeRTOS task function called vLEDTask that declares a variable TickType_t xLastWakeTime and initializes it with xTaskGetTickCount().

FreeRTOS

void vLEDTask(void *pvParameters) {
    TickType_t xLastWakeTime = xTaskGetTickCount();
    // Your code here
}

Need a hint?

Use xTaskGetTickCount() to get the current tick count for timing.

2

Define the delay interval variable

Inside the vLEDTask function, create a variable const TickType_t xDelay500ms and set it to pdMS_TO_TICKS(500) to represent 500 milliseconds delay.

FreeRTOS

void vLEDTask(void *pvParameters) {
    TickType_t xLastWakeTime = xTaskGetTickCount();
    const TickType_t xDelay500ms = pdMS_TO_TICKS(500);
    // Your code here
}

Need a hint?

Use pdMS_TO_TICKS(500) to convert 500 milliseconds to ticks.

3

Add the infinite loop with vTaskDelayUntil() and toggle LED

Inside the vLEDTask function, add a for (;;) infinite loop. Inside the loop, call vTaskDelayUntil(&xLastWakeTime, xDelay500ms) to wait precisely. Then toggle the LED by calling ToggleLED().

FreeRTOS

void vLEDTask(void *pvParameters) {
    TickType_t xLastWakeTime = xTaskGetTickCount();
    const TickType_t xDelay500ms = pdMS_TO_TICKS(500);
    for (;;) {
        // Your code here
    }
}

Need a hint?

Use vTaskDelayUntil() with the address of xLastWakeTime and the delay variable.

4

Print a message each time the LED toggles

Inside the infinite loop in vLEDTask, after toggling the LED, add a printf("LED toggled\n") statement to print a message each time the LED changes state.

FreeRTOS

void vLEDTask(void *pvParameters) {
    TickType_t xLastWakeTime = xTaskGetTickCount();
    const TickType_t xDelay500ms = pdMS_TO_TICKS(500);
    for (;;) {
        vTaskDelayUntil(&xLastWakeTime, xDelay500ms);
        ToggleLED();
        // Your code here
    }
}

Need a hint?

Use printf("LED toggled\n") to show the LED toggle event.