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Real-Time Operating System (RTOS): Types, Examples & Features

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

An RTOS (real-time operating system) is an operating system that guarantees a correct result within the specified deadline period.
In other words, we can say that a Real-time operating system is a special-type operating system used in computers with a strict deadline for any specific job or process to be performed.
Results produced after the deadline has passed, even if correct may be of no real value. For e.g.: consider an autonomous robot that delivers mail in an office complex, the vision control system of the robot needs to identify a wall before the robot walks into it, or else the system will be considered as failed.

Uses of Real-Time Operating System:

  1. Real-time operating systems (RTOS) are used in situations to handle real-life scenarios. A few examples of real-time operating systems include
  2. Real-time operating systems are used in airline traffic systems.
  3. Real-time operating systems are used in command control systems.
  4. Real-time operating systems are used in Network multimedia systems.
  5. Also RTOS is used in heart pacemakers, robots, and many more.

Types of Real-Time Operating System:

There are three kinds of RTOS:

1. Hard real-time OS:

A hard real-time OS has the most strict requirements and the degree of tolerance for missed deadlines is negligible. It guarantees critical real-time tasks be completed within their timelines. A missed deadline can result in catastrophic failure of the system.

2. Soft real-time OS:

A soft real-time operating system is a system in which one or more failures meet the deadline, but the performance is considered to be degraded. A soft real-time OS is less restrictive.

3. Firm Real-Time operating systems:

Firm real-time operating systems need to be completed within the deadline and if the result is obtained after the deadline then the result will be considered incorrect. Firm RTOS is used in multimedia applications.
For a life-saving device, like an automatic parachute opening device for skydivers, a delay can be fatal. The parachute opening device deploys the parachute at a specific altitude based on various conditions. If it fails to respond in a specified time, the parachute may not get deployed at all leading to casualty. A similar situation exists during the inflation of airbags, used in cars, at the time of the accident. If airbags don’t get inflated at the appropriate times, it may be fatal for a driver. So such systems must be hard real-time systems, whereas, for TV live broadcasts, a delay can be acceptable. In such cases, soft real-time systems can be used.

Working of Real-time operating systems:

There are different types of properties and functionalities of an RTOS as below:

  • Priority based scheduler: In priority bases scheduling, RTOS assigns the tasks and processes according to the given priority. If the task is having the highest priority then the task will get a CPU faster.
  • Deterministic behavior: In RTOS it doesn’t matter how many tasks there are whether you have 10 or 100 tasks, it doesn’t make any difference, and the highest priority task will be the next.
  • Synchronization and messaging: Synchronization means coordination therefore RTOS provides the communication between tasks of one system to another also the messaging services.
  • System clock interrupts routine: When there are sensitive operations in RTOS, to perform such operations RTOS will provide some sort of system clock.
  • RTOS service: The previous part of the operating system is the kernel. To monitor the hardware tasks, then the kernel manages and allocates the resources.

Why Use an RTOS?

Below are 4 top reasons to consider using an RTOS.

  • Multitasking: For more complex real-time applications, especially those with a code base that is progressively enhanced in each release, the preemptive multitasking design paradigm is superior.
  • Application portability: By providing a standardized set of stack and driver APIs that abstracts the specifics of the underlying hardware, an RTOS makes applications much more portable.
  • System-level debugs and analysis tools: As an application becomes more complex, it becomes more likely that it can behave in unanticipated ways. Excessive memory usage or leaks delayed response to real-time events, or greater than expected CPU loads are all problems that can occur.
  • More efficient use of CPU resources: Simple loop-based run times typically do a lot of polling to check if interrupts have occurred. As a result, a great deal of processor time is occupied doing nothing. Because multitasking RTOS-based applications are interrupt-driven, it is possible to largely eliminate polling from the application.

Terms used in RTOS

Some essential terms used in RTOS 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.

How to Select an RTOS?

  • Performance: The performance of RTOS plays a crucial factor to consider when selecting an RTOS. When it comes to performance, developers have a variety of factors to consider in RTOS.
  • Features: Every RTOS has different features and developers need to evaluate which features are the most important feature to the success and select the RTOS 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 RTOS come with middleware components or have third parties who have developed components that integrate into the RTOS.
  • Engineering Team: The characteristic of RTOS selection that is probably the most common to overlook is the engineering team.

Characteristics of Real-time System:

  • Correctness: It is one of the precious parts of a real-time operating system. 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 systems:

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

Advantages of Real-time operating systems:

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

Disadvantages of Real-Time Operating System

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

Applications of Real-Time Operating Systems

  • Real-time Operating systems are used in:
  • RTOS 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

Real-Time Operating System FAQs

1. Differences between Soft RTOS and Hard RTOS.

Hard real-time OS: The size of the data file in a hard time is small or medium and in this RTOS the response time is in milliseconds. Safety is critical in hard RTOS.
Soft real-time OS: The size of the data file in a soft real-time operating system is large and the response time is higher. System safety is not critical in soft RTOS.

2. Is window a Real-time operating system?
Microsoft windows are not real-time They are often completely unresponsive for seconds at a time. They indicate this condition by displaying an hourglass or a clock symbol or by simply refusing to respond to mouse clicks or keyboard input.

3. Is android a real-time operating system?
No, Android is not a Real-Time Operating System. An OS should be time deterministic and thereby be predictable to become RTOS.

4. Is Linux real time operating system?
No, Linux is not an RTOS. 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.

5. Why RTOS is preferred?
An RTOS can guarantee the timing requirements for processes under its control, has low latency, is predictable in that it can determine a task’s completion time with certainty, and enables the coexistence of both time-critical and non-time-critical tasks.

This article tried to discuss the concept of RTOS. Hope this blog helps you understand it. To practice more problems you can check out MYCODE | Competitive Programming.

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