C Real-Time Programming Tutorial

1. Introduction to Real-Time Programming

Real-time programming involves creating systems that respond to inputs or events within a strict time constraint. These systems are crucial for applications such as embedded systems, robotics, and control systems.

In C, real-time programming requires careful management of hardware and software resources, especially for tasks like interrupt handling and precise timing.

2. Time-Driven Scheduling

Real-time tasks often need to be executed at regular intervals. A simple approach is to use timers and scheduling to ensure tasks are completed on time.

#include <stdio.h>
#include <unistd.h>  // for sleep()

void task() {
    printf("Task executed\n");
}

int main() {
    while(1) {
        task();
        sleep(1);  // Delay the task by 1 second
    }
    return 0;
}
                

In the above code, the task is executed every second using the `sleep()` function, which is suitable for low-precision real-time applications.

3. Interrupt Handling

Interrupt handling is a critical aspect of real-time systems. It allows a system to immediately respond to an event by suspending its current task and executing an interrupt service routine (ISR).

#include <stdio.h>
#include <signal.h>
#include <unistd.h>

void interrupt_handler(int sig) {
    printf("Interrupt handled!\n");
}

int main() {
    signal(SIGINT, interrupt_handler);
    while(1) {
        printf("Waiting for interrupt...\n");
        sleep(1);  // Simulate doing other work
    }
    return 0;
}
                

In this example, the program waits for an interrupt signal (SIGINT) and calls the `interrupt_handler()` function when the interrupt occurs.

4. Real-Time Operating Systems (RTOS)

In more complex real-time applications, you may need to use a Real-Time Operating System (RTOS) that provides built-in scheduling and resource management for time-critical tasks.

Popular RTOS options include FreeRTOS, RTX, and embOS, which offer features such as task prioritization and inter-task communication.

5. Conclusion

Real-time programming in C is essential for applications where timing is crucial. By leveraging techniques like scheduling, interrupts, and RTOS, you can ensure that your system meets its real-time requirements.