Fundamentals of Real-Time Operating System Programming in C

In the field of embedded systems and industrial control, the concept of a Real-Time Operating System (RTOS) is very important. They ensure that tasks are completed within a specific time frame, thus meeting strict timing requirements. This article will introduce the fundamentals of RTOS programming in C and provide code examples to help readers understand.

What is a Real-Time Operating System?

A Real-Time Operating System is one that can handle events and respond to them within a specified time. Unlike traditional general-purpose operating systems, RTOS emphasizes task scheduling and response time. In an RTOS, tasks are often referred to as “threads” or “processes,” which can execute concurrently.

Classification of Real-Time Systems

1. Hard Real-Time: Tasks must be completed within the specified time; otherwise, severe consequences may occur.
2. Soft Real-Time: Tasks should be completed within the specified time, but occasional delays are acceptable.

Basic Concepts of RTOS

Task

A task is the basic execution unit in an RTOS, with each task having its own priority, state, and stack space.

Scheduler

The scheduler is responsible for managing multiple tasks and deciding which task gets CPU resources based on priority. Common scheduling algorithms include:

• Priority Scheduling
• Round Robin
• Shortest Job First, etc.

Semaphore

A semaphore is used to control access to shared resources to avoid race conditions. It can be divided into two types: binary semaphores and counting semaphores.

RTOS Programming Example in C

We will use FreeRTOS, a popular and open-source RTOS for embedded development. The following code demonstrates how to create two simple tasks and use a binary semaphore for synchronization.

Environment Setup

Ensure that you have installed FreeRTOS and configured your development environment. If you are using the Arduino IDE, you can directly download the FreeRTOS library for testing.

Example Code

#include <stdio.h>
#include "FreeRTOS.h"
#include "task.h"
#include "semphr.h"
// Define semaphore
SemaphoreHandle_t xBinarySemaphore;
// Producer task
void vProducerTask(void *pvParameters) {
    for (;;) {
        printf("Producing data...\n");
        // Simulate data production process
        vTaskDelay(pdMS_TO_TICKS(1000));
        // Release semaphore to notify consumer
        xSemaphoreGive(xBinarySemaphore);
    }
}
// Consumer task
void vConsumerTask(void *pvParameters) {
    for (;;) {
        // Wait to take semaphore, block if none available
        if (xSemaphoreTake(xBinarySemaphore, portMAX_DELAY) == pdTRUE) {
            printf("Consuming data...\n");
            // Simulate data consumption process
            vTaskDelay(pdMS_TO_TICKS(500));
        }
    }
}
int main(void) {
    // Create binary semaphore
    xBinarySemaphore = xSemaphoreCreateBinary();
    // Create producer and consumer tasks
    xTaskCreate(vProducerTask, "Producer", configMINIMAL_STACK_SIZE, NULL, 1, NULL);
    xTaskCreate(vConsumerTask, "Consumer", configMINIMAL_STACK_SIZE, NULL, 1, NULL);
    // Start scheduler to run all created tasks
    vTaskStartScheduler();
    for (;;); // Program will not reach here
}

Code Explanation

1. Include Header Files: Include necessary FreeRTOS header files.
2. Define Semaphore: <span>xBinarySemaphore</span> is used to implement data synchronization between producer and consumer.
3. Producer Function <span>vProducerTask</span>:

• Simulates data generation in an infinite loop, printing information every second.
• Uses <span>xSemaphoreGive()</span> function to release the semaphore, notifying the consumer that new data is available.

Consumer Function <span>vConsumerTask</span>:

• In an infinite loop, calls <span>xSemaphoreTake()</span> to wait for the semaphore; if successful, it consumes data and prints information.

Main Function <span>main</span>:

• Creates a binary semaphore and two independently running threads (producer and consumer).
• Starts the scheduler to let all created threads begin working.

Conclusion

This article introduced the fundamentals of RTOS programming in C, including what a real-time operating system is, its basic concepts, and how to use FreeRTOS for simple application development. Through this example, you should have a preliminary understanding of how to create multithreaded programs and how to use synchronization mechanisms to coordinate data exchange between different threads. This is just a starting point, and I hope it inspires you to delve deeper into embedded development and real-world application issues!