Differences between the characteristics of a soft real time task

Ques 1:-Explain the key differences between the characteristics of a soft real time task such as web browsing and a non real time task such as e-mail delivery?

ANS= Key Concepts

Classification Of Real-Time Systems

Real-Time systems can be classified from different perspectives. The first two classifications, hard real-time versus soft real-time, and fail-safe versus fail-operational, depend on the characteristics of the application, i.e., on factors outside the computer system. The second three classifications, guaranteed-timeliness versus best-effort, resource-adequate versus resource-inadequate, and event-triggered versus time-triggered, depend on the design and implementation, i.e., on factors inside the computer system. However this paper focuses on the differences between hard and soft real-time classification.

Hard Real-Time versus Soft Real-Time

The response time requirements of hard real-time systems are in the order of milliseconds or less and can result in a catastrophe if not met. In contrast, the response time requirements of soft real-time systems are higher and not very stringent. In a hard real-time system, the peak-load performance must be predictable and should not violate the predefined deadlines. In a soft real-time system, a degraded operation in a rarely occurring peak load can be tolerated. A hard real-time system must remain synchronous with the state of the environment in all cases. On the otherhand soft real-time systems will slow down their response time if the load is very high. Hard real-time systems are often safety critical. Hard real-time systems have small data files and real-time databases. Temporal accuracy is often the concern here. Soft real-time systems for example, on-line reservation systems have larger databases and require long-term integrity of real-time systems. If an error occurs in a soft real-time system, the computation is rolled back to a previously established checkpoint to initiate a recovery action. In hard real-time systems, roll-back/recovery is of limited use.

Ques2:-Name any two important sensors devices and two actuator devices use in real time applications and explain the physical principals behind their working?

ANS= one actuator is robotic arms that is mainly used in the manufacture company of any car and bike..the robotic adjust the parts of car inside the cabenet…

Input=tempreture ,,,pressure,light,etc its all the input of for the actuator…

Output=electrical signal

Ques3:-:- In a hard real time system, is it necessary that every task in the system be of hard real time type? Explain your answer using a suitable example?

Ans:-Contain only tasks with no hard timing constraints.Also known as “best effort” systemsMost modern operating systems can serve as the base for a soft real time systems.Examples:multimedia transmission and reception, networking, telecom (cellular) networks,web sites and services, computer games.

Contains tasks with hard timing constraints.Requires formal verification/guarantees of being to always meet its hard deadlines (except for fatal errors).

Examples:air traffic control , vehicle subsystems control, medical systems

There are two different execution models:

In a preemptive model of execution a task may be interrupted (preempted) during its execution and another task run in its place.

In a non-preemptive model of execution after a task that starts executing no other task may execute until this task concludes or yields the CPU.

The task model for a real time system has two main types:

Ques4:-What are the different types of timing constraints that occur in a system? Give examples of each.

Time constraints of data:-The controlling system interacts with its environment based on the data available about the environment, say from various sensors e.g position , velocity, and altitude, sensors and cameras. It is known that the state of the environment, as perceived by the controlling system, be consistent with the actual state of the environment. The second data is processed further to derive new data, for example data such as aircraft position, heading velocity are used to derive the time at which it would touch ground if allowed to land.

Time constraints of actions:- having covered the timing aspects of events and data we are now in a position to summarize the reasons for actions being associated with time constraints. Time constraints dictate the behaviour of the environment they constrain the rates and time at which input arrive at the system for example in an air traffic control system, a flight commander must not ask for permission to land until the aircraft is 10 minutes from the airport.

Behavioral constraints ensure that the environment of a system is well behaved, whereas performance constraints ensure that the computer system performs satisfactorily.

Each of performance and behavioral constraints can further be classified into the following three types:

  • Delay Constraint
  • Deadline Constraint
  • Duration Constraint

These three classes of constraints are explained in the subsequent sections.

Ques5:-Explain why safety and reliability are not independent issues in safety-critical hard real time systems. Explain the basic techniques you would adopt to develop a software product that is required to be highly reliable

Ans:- it will crash, and it wastes lot of time and money to create a new system, and if the system is crash it will not work as a real time system ,it loses the reliability ,therefore it is necessary to hard real time systems that safety and reliability depends on each other, thus system works as a true hard real time system.

In traditional systems ,safety and reliability are normally considered to be independent issues .it is therefore possible to identify a traditiona system that is safe and unreliable and systems that are reliable but unsafe.for ex- word processing software may not be a reliable but is safe, Software Reliability is an important to attribute of software quality, together with functionality, usability, performance, serviceability, capability, installability, maintainability, and documentation. Software Reliability is hard to achieve, because the complexity of software tends to be high. While any system with a high degree of complexity, including software, will be hard to reach a certain level of reliability, system developers tend to push complexity into the software layer, with the rapid growth of system size and ease of doing so by upgrading the software. For example, large next-generation aircraft will have over one million source lines of software on-board; next-generation air traffic control systems will contain between one and two million lines; the upcoming international Space Station will have over two million lines on-board and over ten million lines of ground support software; several major life-critical defense systems will have over five million source lines of software. While the complexity of software is inversely related to software

Ques6:-Give an example of soft real time task and non real time task. Explain the difference in between these two types of tasks?

Ans:- A soft real-time system on the other hand will tolerate such lateness, and may respond with decreased service quality (e.g., omitting frames while displaying a video). Soft real-time systems are typically used where there is some issue of concurrent access and the need to keep a number of connected systems up to date with changing situations;a non real time tasks are batch processing jobs,e -mail,and background tasks such an event logers .you may ,however ,argue that even these tasks, in the strict sense of the term ,do have certain time bounds.an email is expected to reach its destination at least with in a coupleof hours of being sent.similar is the case with a batch processing job such a pay-slip printing what then reality is the difference between a non real task and a soft real time task for non real time tasks ,the associated time bounds are typically of the order of a few minutes hours or even days .in contrast the time bounds associated with soft real time tasks are at most of the order

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