How can operating systems better support real-time applications?

Some ways to get started with RTOS: - Choose an RTOS - Understand the RTOS concepts - Select the hardware - Set up the development environment - Write the code - Test the application - Debug the application - Deploy the application

Um sistema operacional em tempo real (RTOS) é projetado para atender a requisitos específicos de tempo em que a resposta rápida é essencial. Diferente dos sistemas operacionais convencionais, o RTOS garante determinismo, prioridades de tarefas, escalonamento preditivo e eficiente gerenciamento de interrupções. Ele é utilizado em aplicações onde prazos rigorosos precisam ser cumpridos, como em sistemas de controle industrial, navegação em aeronaves, equipamentos médicos e automação, garantindo eficiência e confiabilidade em ambientes que exigem operações em tempo real.

A Real-Time Operating System (RTOS) is a lightweight OS used to ease multitasking and task integration in resource and time constrained designs, which is normally the case in embedded systems. Besides, the term “real-time” indicates predictability/determinism in execution time rather than raw speed, hence an RTOS can usually be proven to satisfy hard real-time requirements due to its determinism.

A real time OS is a special kind of OS that can do things very fast and on time. It is used for things that need to react quickly to events, like robots, machines or games. A real time OS can: Decide which tasks are more important and do them first. Switch between tasks when something happens, like a button press or a sensor reading. Give enough memory and resources to each task. Share things, like files or devices, among tasks without problems.

A Real-Time Operating System (RTOS) is an operating system specifically designed to meet the stringent requirements of real-time systems. Real-time systems must respond to inputs or events within a specified time frame to ensure correct and predictable behavior. RTOS is crucial in applications where timing constraints are critical, such as industrial control systems, embedded systems, robotics, medical devices, and aerospace.

A explicação anterior abordou de maneira abrangente os principais desafios dos aplicativos em tempo real, como contenção de recursos, não-determinismo e complexidade. No entanto, é relevante mencionar que a garantia de segurança e confiabilidade também é crítica nesse contexto, pois falhas podem ter consequências graves. Além disso, aspectos relacionados à escalabilidade e à gestão eficiente de eventos em tempo real são pontos adicionais que não foram especificamente detalhados na explicação anterior..

Real-time applications are challenging because they require high precision and accuracy. They must respond within the critical time frame failing which the system may face severe consequences. This could be as simple as audio/video running out of sync or as catastrophic as an industrial process going out of control.

the challenges in developing real-time applications underscore the intricate interplay between timing constraints and deterministic behavior. Predictability, resource management, concurrency, fault tolerance, hardware limitations, testing, adaptability, software complexity, and cost constraints collectively shape the landscape of challenges faced by developers in this specialized domain. Navigating these challenges requires a holistic approach, where each facet is meticulously addressed to ensure the successful development and deployment of real-time applications.

Real-time applications pose various challenges for the OS, such as: - Resource contention: Real-time applications compete for the same resources, such as CPU, memory, disk, or network, which can lead to delays, bottlenecks, or starvation for some tasks. - Non-determinism: The OS cannot predict or control the behavior of certain components that may affect the timing and performance of real-time applications. - Complexity: Real-time applications have complex dependencies, interactions, or requirements that are hard to model, test, or verify. For instance, a real-time application may need to coordinate with multiple sensors, actuators, or other applications in a distributed system.

Real-time applications are programs that need to work fast and correctly, like controlling a car or a machine. They are challenging because: 1- They need special skills and tools to build them12. 2- They need to handle many events and tasks at the same time. 3- They need to avoid errors and delays that can cause problems. These are the some reason "Why real-time applications are challenging".

Real-time apps are classified by timing needs: 1. Hard Real-Time: Strict deadlines, failure intolerant (e.g. aerospace). 2. Soft Real-Time: Timeliness important, occasional misses tolerated (e.g. streaming). 3. Firm Real-Time: Allows some deadline misses (e.g. financial trading). 4. Event-Driven: Triggered by events, rapid response (e.g. sensor networks). 5. Time-Sharing: Multiple tasks share resources, responsiveness crucial (e.g. general-purpose computing). 6. Control Systems: Focus on real-time control (e.g. industrial control). 7. Embedded Real-Time: Real-time functions in larger systems (e.g. IoT). 8. Distributed Real-Time: Tasks distributed across nodes (e.g. telecom networks).

Real-time applications are programs that need to work fast and on time, like controlling a car or a machine. They can be classified into two types: Hard real-time applications: These are the programs that must finish their tasks before a strict deadline, otherwise they can cause serious problems or failures. For example, a flight control system or a pacemaker. Soft real-time applications: These are the programs that should finish their tasks before a deadline, but they can tolerate some delays or errors. For example, a video streaming service or a online game.

Real-time applications can be classified into two types: Hard and Soft. Hard real-time systems are those that absolutely must meet their deadline. In contrast, soft real-time systems can miss their deadline without catastrophic consequences, although the value of the result might be diminished.

Strictly speaking a “hard” RT system must guarantee that computations are finished by the certain required time. In the other words the system reaction time on event should be small and guaranteed. If one controls a mechanical system PID code should always be executed within the loop time period. This is the case for Industrial and Medical applications. For some systems this is accomplished by using HW accelerators. For the “soft” RT cases like video/audio some data loss might be acceptable (causing artifacts on the screen and clicks on the phone). So, heavy buffering with the penalty of some data latency is OK.

Real time applications are classified under either soft real-time or hard real-time. The difference is hard RTOS considers inability to meet its deadline a failure, and may cause severe consequences eg autopilot systems, which soft RTOS can tolerate few missed deadlines

Some techniques include: Task scheduling (monotonic scheduling, earliest deadline first or EDF) Interrupt handling - ensures timely response to external events without compromising the system Resource management - develop strategies to manage shared resources and prevent resource conflicts ....

RTOS design often involves the use of various scheduling techniques and extensions to ensure that tasks are executed within a specified deadline. Here are some of the commonly used scheduling techniques: - Preemptive scheduling: This technique allocates CPU time to tasks based on their priority and deadline, allowing higher-priority tasks to take precedence when needed. - Fixed-priority scheduling: This technique assigns a fixed priority to each task based on its importance and criticality. - Rate-monotonic scheduling: This technique assigns priority to tasks based on their frequency or period. - Time-slicing: This technique divides the CPU time into small slices or quanta and assigns each slice to a task based on its priority and deadline.

Common techniques for real-time OS design include preemptive multitasking, priority scheduling, and resource reservation. Preemptive multitasking allows the system to interrupt one task in favour of a higher priority task. Priority scheduling ensures that tasks with higher urgency are executed before those with lower urgency. Resource reservation helps in avoiding resource-related bottlenecks.

There are very few things one can do. The key is the scheduler to support multiple threads. The scheduling algorithm can use preemption, priorities, cooperative run-to-completion, and so on. However, nothing can prevent a developer from over-running the task queue, using all available memory resources, or blocking a motor-control loop task on a semaphore that has never been given by another tread in case of error or priority inversion. So, in this domain the careful and simple system design and exhaustive testing are essential to avoid potential catastrophic consequences. Following coding standards like MISRA is a good start.

Several techniques are employed to meet the timing requirements of real-time applications: 1. Prioritization: - Assigning priority levels to tasks helps ensure critical processes are executed first, meeting their deadlines. 2. Scheduling Algorithms: - Using specialized scheduling algorithms, such as Rate Monotonic Scheduling (RMS) or Earliest Deadline First (EDF), helps optimize task execution based on deadlines. 3. Resource Allocation: - Efficiently managing resources like CPU time, memory, and I/O is crucial to prevent bottlenecks and delays. 4. Hardware Support: - Utilizing hardware features like timers, interrupts, and dedicated co-processors can enhance real-time performance.

1. **FreeRTOS:** Um sistema operacional de código aberto para sistemas embarcados em tempo real, conhecido por sua portabilidade e eficiência. 2. **RTOS (Real-Time Operating System) embutido em microcontroladores:** Muitos fabricantes de microcontroladores incorporam sistemas operacionais em tempo real diretamente em seus dispositivos, como o VxWorks para processadores Wind River. 3. **QNX:** Utilizado em sistemas críticos, como na indústria automotiva e equipamentos médicos. Esses sistemas são adaptados para atender a requisitos específicos de determinismo, previsibilidade e resposta em tempo real, fundamentais em aplicações críticas.

Examples of real-time operating systems include FreeRTOS, VxWorks, and RTLinux. These systems are designed to provide robust and deterministic performance, making them suitable for a wide range of time-critical applications.

FreeRTOS: Popular open-source option, easy to use and learn, ideal for simple projects. Zephyr: Lightweight and modular RTOS from the Linux Foundation, suitable for resource-constrained devices. Chibios: Open-source and feature-rich RTOS for ARM Cortex-M microcontrollers.

I had a few interesting personal experiences in the past that changed my perspective regarding the seriousness of safety in the RT design. One of those SW problems led to a 200 lb bar of a large industrial moving stage flew over my head. The second time a robot threw a silicon wafer. The edge of the wafer got deep into the wall. It is a good thing nobody was standing in the way. I was lucky in those situations. However, luck is not something engineers should rely upon when designing critical RT applications.