Real-time Operating System

Real-time operating systems are important topics from the interview point of view. This article includes real-time operating system types and their examples. It also includes applications of real-time systems.

A real-time operating system (RTOS) is designed to accommodate real-time applications that process data as it arrives, often without buffering delays. The RTOS calculates the required processing time in tenths of a second. This time-bound system can be defined as a fixed time constraint. In this type of system, processing must occur within specified constraints. Otherwise, the system will fail.

A real-time operating system (RTOS) is an operating system that executes tasks with strict time deadlines. By contrast, a batch operating system (BOS) can delay or stall tasks to achieve greater performance. While most tasks in our computer systems are real-time, they don’t have to be. Many systems can become sluggish without drastic changes. However, some tasks must run at precise intervals to work effectively. For this reason, the term real-time has become synonymous with instantaneous execution.

Table of Content

• What is a Real-time Operating System?
• Why use Real-time Operating System?
• Types of Real-time Operating System
• Advantages of Real-time Operating System
• Disadvantages of Real-time Operating System
• Applications of Real-time Operating System

What is a Real-time Operating System?

A real-time operating system (RTOS) is an operating system that executes tasks with strict time deadlines. By contrast, a batch operating system (BOS) can delay or stall tasks to achieve greater performance. While most tasks in our computer systems are real-time, they don’t have to be. Many systems can become sluggish without drastic changes. However, some tasks must run at precise intervals to work effectively. For this reason, the term real-time has become synonymous with instantaneous execution. Examples are VxWorks, QNX, eCos, RT Linux

Why use Real-time Operating System?

• It will be deterministic in nature as to when and how that task will run given whatever conditions are defined for it to do so. A non-real time OS makes no such guarantees, and critical tasks can fail under them as they won’t be guaranteed execution time or access to resources.
• The RTOS uses certain sophisticated algorithms to schedule normally running, ready, and blocked states that are more focused on application development than scheduling.
• You might see them used in various embedded systems, typically those with sensors that need to execute tasks whenever a certain variable changes.
• The RTOS offers modular task-based development that enables modular task-based testing. A task-based API promotes modular development as tasks.
• The RTOS has many drivers that can be used directly for various applications.
• The RTOS is event-driven and doesn’t waste time processing events that never happen and also no resources are used for processing the event which does not occur.

Important terms used in Real-time Operating System

• Tasks- A set of related tasks that together can provide some system functionality.
• Jobs-Jobs are small pieces of work that can be assigned to editors and may or may not require resources.
• Job Release Time-The time when the job is ready to run.
• Job Execution Time– How long it takes for the job execution to complete
• Job Deadline-The time to finish running the job.
• Job Response Time– The time from the job release time to the end of the instant. Absolute deadline: This is a relative deadline and includes the release date.

Types of Real-time Operating System

1. Hard Real Time

In a hard RTOS, deadlines are so tight that the execution of specific tasks must start at a specific scheduled time and be completed within the allotted time. Suppose the task is to be completed at the 5th second, then it should not be completed before or after the 5th second and instead on the exact 5th second.

Examples: 

Let’s take an example of an airbag that a car manufacturer offers along with the driver’s steering wheel. If the driver applies the brakes at a given moment, the airbag deploys and prevents the driver’s head from hitting the steering wheel. A delay of even one millisecond would have led to an accident. 

Similarly, think about stock trading software. If someone wants to sell a particular stock, the system must ensure that the command is executed within a certain critical time. Otherwise, traders could suffer huge losses if the market suddenly drops.

2. Fixed Real Time

RTOS of this type must also meet deadlines. However, while passing the deadline does not have much impact, it can have undesirable effects, such as a significant reduction in product quality—for example, various kinds of multimedia applications,video conferencing, latency may degrade the quality of a call, but the computer system is still usable.

3. Soft Real Time

A soft real-time RTOS tolerates operating system delays. This type of RTOS gives deadlines to certain jobs but can tolerate small-time delays. Therefore, this type of RTOS handles deadlines gracefully. But yes, if the deadline is missed multiple times, that can lead to system failure.

Example-A video game is an example of a soft real-time system. Video games rely on user input and have limited time to process; degradation is sometimes expected for this reason.

Advantages of Real-time Operating System

1. Reduced downtime

An RTOS ensures that the system uses more resources while maintaining all devices in active condition. As a result, minimal downtime occurs when using RTOS. Additionally, hosting firms that use RTOS also show the best outcomes.

2. Task Administration

It usually takes less time for a real-time operating system to switch from one task to another. Task switching often occurs in 3 microseconds or less. Critical processes can be completed on time thanks to task management that moves more quickly.

3. Availability

An RTOS system is accessible 24/7 because it produces the best outcomes. As a result, it is ideal for applications that must run continuously. In addition, various MCU (Microcontroller) platforms can be supported by an RTOS system.

4. Dependability

Real-time operating systems, particularly those of hard RTOS, are error-free. It guarantees a better method of handling mistakes. Additionally, operating systems encounter a jitter problem, where the number of mistakes between each loop is counted. An RTOS can be improved so that it experiences fewer jitters if properly programmed. Effectiveness

Disadvantages of Real-time Operating System

1. Multitasking 

An RTOS can focus on the target application but not when it comes to multitasking. They are designed to perform only a few tasks. Therefore, it is not recommended for systems that require multitasking. 

2. Driver request 

Real-time operating systems always have signal interruptions. Therefore, the necessary drivers must be installed on your computer to achieve a certain speed. When an interrupt occurs, the RTOS can use drivers to respond quickly.

3. Program crashes 

Frequent program crashes can occur when using a real-time operating system. Unlike regular operating systems, RTOS cannot effectively separate storage domains. As a result, processes have trouble dealing with them.

4. Task focus 

RTOS focuses on one application at a time. This is primarily done to maintain accuracy and reduce errors. All other low-priority applications must wait. There is no waiting time limit. 2. Complex, complicated algorithms are behind the RTOS interface. It is difficult for ordinary users to create these algorithms. Only experienced developers can write and understand them.

Applications of Real-time Operating System

1. Medical Science application

• Robot
• MRI Scan
• Radiation therapy etc.

2. Peripheral Equipment applications

• Laser printer
• Fax machine
• Digital camera etc.

3. Telecommunication applications

• Cellular system
• Video Conferencing etc.

4. Defense applications

• Missile guidance system
• Anti-missile system
• Satellite missile system etc.

5. Aerospace applications

• Satellite tracking system
• Flight simulation etc

Difference between Hard Real-time and Soft Real-time Operating System

Conclusion

Real-time processing ensures that all relevant data is available at the right moment and in the correct format for decision-making. As technology advances make microprocessors faster and more powerful, optimizing your computer systems for real-time performance without sacrificing power or flexibility is essential.