• Journal of Korea Multimedia Society
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• v.13 no.9
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• pp.1285-1298
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• 2010

Since the TinyOS incorporating a non-preemptive task scheduling policy uses a FIFO (First-In First-Out) queue, a task with the highest priority cannot preempt a task with lower priority before the task with lower priority must run to completion. Therefore, the non-preemptive TinyOS cannot guarantee the completion of real-time user tasks within their deadlines. Additionally, the non-preemptive TinyOS needs to meet the deadlines of user tasks as well as those of TinyOS platform tasks called by user tasks in order to guarantee the deadlines of the real-time services requested by user tasks. In this paper, we present a group-based real-time scheduling technique that makes it possible to guarantee the deadlines of real-time user tasks in the TinyOS incorporating a non-preemptive task scheduling policy. The proposed technique groups together a given user task and TinyOS platform tasks called and activated by the user task, and then schedule them as a virtual big task. A case study shows that the proposed technique yields efficient performance in terms of guaranteeing the completion of user tasks within their deadlines and aiming to provide them with good average response time, while maintaining the compatibility of the existing non-preemptive TinyOS platform.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.10
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• pp.3423-3438
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• 2014

In recent years, wearable sensor devices are reshaping the way people live, work, and play. A wearable sensor device is a computer that is subsumed into the personal space of the user, and is always on, and always accessible. Therefore, among the most salient aspects of a wearable sensor device should be a small form factor, long battery lifetime, and real-time characteristics. Thereby, sophisticated applications of a wearable sensor device use real-time operating systems to guarantee real-time deadlines. The deterministic multi-dimensional task scheduling algorithms are implemented on ARC (Actual Remote Control) with relatively limited hardware resources. ARC is a wearable wristwatch-type remote controller; it can also serve as a universal remote control, for various wearable sensor devices. In the proposed algorithms, there is no limit on the maximum number of task priorities, and the memory requirement can be dramatically reduced. Furthermore, regardless of the number of tasks, the complexity of the time and space of the proposed algorithms is O(1). A valuable contribution of this work is to guarantee real-time deadlines for wearable sensor devices.

• Journal of the Korea Society of Computer and Information
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• v.12 no.3
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• pp.147-153
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• 2007

Task scheduling is an essential part of any computer system for allocating tasks to a processor of the system among various competitors. As we know, in real-time system, the failure of scheduling a hard real-time task my lead to disastrous consequence. Besides efficiency, resource and speed, real-time system has to take time constraint in serious consideration. This paper proposes a priority-driven scheduling algorithm for real-time multiprocessor system. which is called L-RE coordinates algorithm. L-RE coordinates is a new way of describing the task scheduling problem. In the algorithm, we take both deadline and laxity into consideration for allocating the priority. The simulation result shows that the new algorithm is viable and performance better than EDF and LLF algorithm on schedulability and context switch respectively.

• International Journal of Internet, Broadcasting and Communication
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• v.9 no.2
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• pp.78-86
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• 2017

In this paper, we propose an energy-efficient scheduling scheme for real-time periodic tasks on a heterogeneous Grid computing system. The Grid system consists of heterogeneous processors providing the DVFS mechanism with a finite set of discrete clock frequencies. In order to save energy consumption, the proposed scheduling scheme assigns each real-time task to a processor with the least energy increment. Also the scheme activates a part of all available processors with unused processors powered off. Evaluation shows that the proposed scheme saves up to 70% energy consumption of the previous method.

• The KIPS Transactions:PartA
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• v.8A no.1
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• pp.16-26
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• 2001

This paper proposes an extended scheduler model that is an extension of the existing model proposed already in [4, 5], which consists of upper layer task scheduler and lower layer scheduling framework. However, in order to support aperiodic task scheduling, the task scheduler has been divided into two parts, such as periodic task control component and aperiodic task control component. Thus, the proposed model can support various bandwidth-preserving servers that can service aperiodic tasks. The model distinctly separates a classic monolithic kernel scheduler into several kernel components according to their functionality. This enables system developers to implement a new scheduling algorithm or aperiodic task server independent of complex low kernel mechanism, and reconfigure the system at need. In Real-Time Linux [6], we implemented the proposed scheduling framework representative scheduling algorithms, and server bandwidth-preserving servers on purpose to test. Throughout these implementations, we confirmed that a new algorithm or server could be developed independently without updates of complex low kernel modules. In order to verify efficiency of the proposed model, we measured the performance of several aperiodic task servers. The results showed this the performance of model, which even consisted of two hierarchical components and several modules, didnt have such high run-time overhead, and could efficiently support reconfiguration and scheduler development.

• IEMEK Journal of Embedded Systems and Applications
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• v.6 no.1
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• pp.41-47
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• 2011

The Pfair scheduling algorithm, which is an optimal scheduling algorithm in the hard real-time multiprocessor environments, propose the necessary and sufficient condition for the schedulability and is based on the fixed quantum size. Recently, several methods that determine the optimal quantum size dynamically were proposed in the mode change environments. But these methods considered only the case in which the period of a task is increased or decreased. In this paper, we also consider the case in which the execution time of a task is increased or decreased, and propose new methods that determine the optimal quantum size dynamically.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.11
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• pp.1333-1343
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• 1999

경성 실시간 시스템의 태스크들은 논리적으로 올바른 결과를 산출해야 하지만 또한 각자의 시간 제한 조건을 만족하여야 한다. 간격제한 스케줄링은 시간 제한 조건이 시간 간격 제한으로 주어지는 실시간 태스크들을 스케줄하기 위하여 도입되었다. 간격제한 스케줄링에서의 각 태스크들은 시간 간격 제한 조건을 갖는데, 이것은 태스크의 두 연속적인 수행의 종료시간에 대해 제한을 가한다. 다시 말해, 간격제한 스케줄링에서의 각 태스크 수행은 그 태스크의 직전 수행 완료 시간으로부터 발생하는 데드라인을 갖는다. 간격제한 태스크 스케줄링에 관한 많은 연구는 단순화 방법에 기초하고 있다. 그러나, 우리는 이 논문에서 단순화 방법을 사용하지 않고, 정적 우선순위 및 정적 분리 제한 정책을 채용한 새로운 간격제한 태스크 스케줄링 방법을 제안한다. 제안된 정적 할당 방법은 스케줄링 분석 및 구현을 매우 간단히 할 수 있으며, 또한 스케줄러의 실행시간 오버헤드를 줄일 수 있다.Abstract Tasks in hard real-time systems must not only be logically correct but also meet their timing constraints. The distance-constrained scheduling has been introduced to schedule real-time tasks whose timing constraints are characterized by temporal distance constraints. Each task in the distance-constrained scheduling has a temporal distance constraint which imposes restriction on the finishing times of two consecutive executions of the task. Thus, each execution of a task in the distance-constrained scheduling has a deadline relative to the finishing time of the previous execution of the task.Much work on the distance-constrained task scheduling has been based on the reduction technique. In this paper, we propose a new scheme for the distance-constrained task scheduling which does not use the reduction technique but adopts static priority and static separation constraint assignment policy. We show that our static assignment approach can simplify the scheduling analysis and its implementation, and can also reduce the run-time overhead of the scheduler.

• Journal of Electrical Engineering and information Science
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• v.3 no.3
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• pp.396-401
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• 1998

An optimal algorithm is presented for feasibility test and scheduling of real-time tasks where tasks are preemptable and created dynamically. Each task has an arbitrary creation time, ready time, maximum execution time, and deadline. Feasibility test and scheduling are conducted via the same algorithm. Time complexity of the algorithm is O(n) for each newly created task where n is the number of tasks. This result improves the previous result of O(n log n). It is shown that the algorithm can be used for scheduling tasks with different levels of importance. Time complexity of the algorithm for the problem is O(n\ulcorner) which improves the previous results of O(n\ulcorner log n).

• Journal of Korea Multimedia Society
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• v.14 no.1
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• pp.76-84
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• 2011

Embedded Systems need to ensure real-time of the task response time depending on the applied fields of it. And task could be faulty due to various reasons in real time systems. Therefore in this paper, we design a task scheduler that guarantees deadlines of periodic tasks and considers a fault tolerance of defective task in embedded system with a single processor. In order to provide real-time, we classify tasks with periodic/aperiodic tasks and applies RMS(Rate Monotonic Scheduling) method to schedule periodic tasks and can guarantees execution of aperiodic tasks by managing surplus times obtained after analyzing the execution time of periodic tasks. In order to provide fault tolerance, we manage backup times and reexecute a fault task to restore it's conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.351-356
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• 2015

Synthetic utilization on multiprocessor system is not considered periodic tasks, except scheduling methods for aperiodic tasks where one of the real-time aperiodic tasks is a scheduling method. But really aperiodic tasks scheduling method is composed of mixed task types. Aperiodic task scheduling method guarantee an analysis of the schedualibility of aperiodic task. The set of mixed tasks periodic and aperiodic tasks scheduling method uses improved synthetic utilization that is presented in this paper. The new method shows that schedulability increases aperiodic server method.