What is a Real-Time Operating System (RTOS)?

Last Updated on April 20, 2023 by Prepbytes

A real time operating system is a software system that is designed to manage real time applications. Real time applications require immediate responses to inputs and events, and the real time OS is responsible for ensuring that these responses occur in a timely and deterministic manner. In this article, we will discuss what is real time operating system, its uses, types of real time operating system, working of real time OS, real time operating system examples, advantages, and disadvantages of real time operating system.

What is Real Time Operating System?

A real time operating system is a type of operating system used in computing systems that require strict completion deadlines for all tasks that need to be performed. An real time OS is critical in applications that need immediate and deterministic behavior, such as in industrial control systems, aerospace and defense, medical devices, and automotive industries.Overall, an real time operating system ensures that a system is reliable, safe, and efficient.

Why Use an Real Time OS?

Without an real time operating system, it can be challenging to ensure that tasks are executed within their deadlines, and the system may not respond quickly to events and inputs. In safety-critical applications such as aerospace and defense, medical devices, and automotive industries, missed deadlines can result in catastrophic failures. An real time OS provides deterministic behavior, which guarantees that tasks will be completed within their deadlines, ensuring the safety of the system. Additionally, an real time operating system provides predictable behavior, which ensures that tasks are executed in a specific order based on their priority. Overall, an real time operating system ensures that a system is reliable, safe, and efficient.

Types of Real Time Operating Systems

There are three types of real time OS:

1. Hard real time OS:
   A hard real time operating system is a type of real-time system that guarantees that all tasks will be completed within a certain deadline, without exception. These systems are designed to provide deterministic behavior, ensuring that critical tasks are completed on time, every time.

   Hard real-time systems are commonly used in applications where missed deadlines can have serious consequences, such as in aerospace and defense, medical devices, and certain types of industrial automation.

2. Soft real time OS:
   A soft real time operating system is a type of real-time system that does not guarantee that all tasks will be completed within a certain deadline. Instead, it provides the best-effort service, attempting to complete tasks as quickly as possible, but without making any guarantees about response time or deadline completion.

   Soft real-time systems are commonly used in applications where occasionally missed deadlines are tolerable, but overall system performance is important. Some examples of soft real-time applications include multimedia streaming, interactive gaming, and certain types of data processing.

3. Firm real time OS:
   A firm real time operating system (RTOS) is a type of real time system that guarantees that tasks will be completed within a certain deadline but with a degree of flexibility. Unlike hard real time systems that have to meet hard deadlines without exception, firm real time systems can tolerate occasional deadline misses, but they should be infrequent and not affect the overall system operation.

   Firm real time systems are commonly used in applications that require real-time performance but can tolerate occasional deadline misses, such as multimedia systems, gaming systems, and certain types of automation systems.

Working of Real Time Operating Systems

The working of a real time operating system is based on the principle of deterministic behavior, which guarantees that tasks are executed within their deadlines. An real time OS typically employs a preemptive priority-based scheduling algorithm, which means that tasks with higher priorities are executed before tasks with lower priorities.

When a system connected to an external event receives a signal or an interrupt, the real time OS immediately switches the processor’s control to the appropriate task, ensuring a quick response time. The real time operating system then allocates system resources, such as memory and CPU time, to that task to ensure its completion within its deadline. Once the task is completed, the real time OS releases the resources allocated to that task and resumes the execution of the task with the next highest priority.

The real time operating system also provides inter-task communication mechanisms, such as message queues and semaphores, to allow tasks to communicate with each other and synchronize their operations. These communication mechanisms are used to exchange data and signals between tasks and ensure that tasks do not interfere with each other.

Terms used in Real Time Operating System

Some essential terms used in real time operating system are discussed below:

• Task: A set of related tasks that are jointly able to provide some system functionality.
• Job: A job is a small piece of work that can be assigned to a processor, and that may or may not require resources.
• Release time of a job: It’s a time of a job at which the job becomes ready for execution.
• Execution time of a job: It is the time taken by a job to finish its execution.
• Deadline of a job: It’s the time by which a job should finish its execution.
• Processors: They are also known as active resources. They are important for the execution of a job.
• Maximum: It is the allowable response time of a job that is called its relative deadline.
• Response time of a job: It is the length of time from the release time of a job when the instant finishes.
• Absolute deadline: This is the relative deadline, which also includes its release time.

Factors for Selecting an Real Time Operating System

Below mentioned are some factors which explains why we should select an real time operating system.

• Performance: The performance of real time operating system plays a crucial factor to consider when selecting an real time OS. When it comes to performance, developers have a variety of factors to consider in real time OS.
• Features: Every real time OS has different features and developers need to evaluate which features are the most important feature to the success and select the real time OS with those features.
• Ecosystem: A software products ecosystem is a critical piece of the selection process in order to ensure ease of integration, support, and product lifetime.
• Middleware: Many real time OS come with middleware components or have third parties who have developed components that integrate into the real time OS.
• Engineering Team: The characteristic of real time OS selection that is probably the most common to overlook is the engineering team.

RTOS Examples

Here are some RTOS examples:

1. FreeRTOS: FreeRTOS is a popular open-source Real time OS. It is designed for microcontrollers and small embedded systems.
2. VxWorks: VxWorks is a real time operating system developed by Wind River Systems. It is widely used in the aerospace, defense, and industrial automation industries.
3. QNX: QNX is a commercial real time operating system developed by BlackBerry. It is used in mission-critical applications such as automotive, medical devices, and nuclear power plants.
4. ThreadX: ThreadX is a real time operating system developed by Express Logic. It is widely used in consumer electronics, medical devices, and automotive applications.
5. Nucleus RTOS: Nucleus RTOS is a real time operating system developed by Mentor Graphics. It is used in a wide range of applications, including consumer electronics, medical devices, and automotive systems.

These are just a few RTOS examples, there are many other commercial and open-source RTOS available in the market.

Characteristics of Real-time System

• Correctness: It is one of the precious parts of a real time OS. A real time operating system produces a correct result within the given time.
• Safety: Safety is necessary for any system but real time operating system can perform for a long time without failures.
• Time Constraints: In real time operating system, the tasks should be completed within the given time period.
• Embedded: real time operating systems are embedded. Embedded means the system that is designed for a specific purpose by the combination of hardware and software.

Features of Real Time Operating System

• Real time OS occupies very less space.
• The response time of real time OS is predictable.
• It consumes some of the resources.
• In real time OS, the kernel restores the state of the task and passes control of the CPU for that task.

Advantages of Real Time Operating System

• Real time OS is easy to develop and execute in real-time applications.
• The real time operating system working structures are extra compact.
• The real time operating system structures require less memory space.
• Memory allocation in these types of systems is managed easily.
• The types of real time operating system are error-free.

Disadvantages of Real Time Operating System

• Real time OSs have complicated layout principles.
• Real time OSs are very costly to develop.
• Real time OSs are very complex.
• Real time OSs can consume critical CPU cycles.

Applications of Real Time OS

Real Time OS are used in:

• Real time operating system is used in airline reservation systems.
• Air traffic control system.
• Systems that provide immediate updating.
• Used in any system that provides up-to-date and minute information on stock prices.
• Defense application systems like RADAR.
• Networked Multimedia Systems
• Command Control Systems
• Internet Telephony

Conclusion
In conclusion, a real time operating system is a crucial component in various applications that require strict completion deadlines, deterministic behavior, and efficient use of system resources. An real time OS ensures that tasks are completed within their deadlines, high-priority tasks are executed first, and inter-task communication is efficient, resulting in reliable, safe, and efficient systems. The applications of real time OS are diverse, ranging from industrial control systems to medical devices and aerospace and defense. Therefore, real time operating system continues to be a critical technology in modern computing systems.

Real Time Operating System FAQs

Here are some frequently asked questions on real time operating system.

Q1: How does an real time OS differ from a general-purpose operating system?
Ans: An real time operating system is designed for time-critical applications and executes tasks within strict deadlines. In contrast, a general-purpose operating system is designed for a wide range of applications and does not guarantee strict deadlines.

Q2: How does an real time OS handle interrupt requests?
Ans: An real time operating system handles interrupt requests by immediately switching the processor’s control to the appropriate task, ensuring a quick response time to external events.

Q3: What is the role of inter-task communication in an Real time OS?
Ans: Inter-task communication allows tasks to communicate with each other and synchronize their operations. This ensures that tasks do not interfere with each other and operate efficiently.

Q4: Can an real time OS be used in non-real-time applications?
Ans: Yes, an real time operating system can be used in non-real-time applications, but it may not provide significant advantages over a general-purpose operating system.

Q5: Is Linux real time operating system?
Ans: No, Linux is not an real time operating system. Linux is a general-purpose operating system that can be found in many computers, with distributions that have been adapted for use in noncritical embedded systems.