• Journal of KIISE:Computer Systems and Theory
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• v.26 no.4
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• pp.443-454
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• 1999

최소 여유시간 우선(Least-Laxity-First)스케쥴링 알고리즘은 여유시간이 작은 태스트가 높은 우선순위를 갖는 동적 우선순위 스케줄링 방법으로서 단일프로세서 시스템에서 최적임이 증명되었다. 그러나, 이 알고리즘은 최소 여유시간을 가진 태스크가 여러 개 존재하여 여유시간 충돌이 발생한 경우 이 태스크들 간에 빈번한 문맥교환이 발생하게 되는 문제점이 있어 실용적이지 못하다. 본 논문에서 제한하는 최소 여유시간 우선 기반의 최소선점을 갖는 스케줄링 알고리즘(Least-Laxity-First with Minimum Preemption 또는 LLF/MP)은 여유시간이 충돌했을 때에 문맥교환을 최소화함으로써 최소 여유시간 우선 스케줄링 알고리즘의 단점을 해결하였다. LLF/MP 스케줄링 알고리듬은 불필요한 문맥교환을 줄임으로써 시스템 오버헤드로 인한 시스템의 성능 저하를 방지할 수 있고 보다 많은 시스템 자원을 예측 불가능한 비주기적 태스크에게 할당할수 있다.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.4
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• pp.302-307
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• 2012

Real-time systems perform periodic tasks and real-time aperiodic tasks such as alarm processing. Especially the periodic tasks included in control systems such as robots have precedence relationships among them. This paper proposes a new scheduling algorithm based on topological sort and residual time. The precedence relationships among periodic tasks are translated to the priorities of the tasks using topological sort algorithm. During the execution of the system the proposed scheduling algorithm decides on whether or not a newly arrived real-time aperiodic task is accepted based on residual time whenever the aperiodic task such as alarm is arrived. The proposed algorithm is validated using examples.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.1373-1376
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• 2010

최근 국민소득향상, 의학기술의 발달 등 이러한 변화는 건강관리에 관한 연구로 이어져 라이프 케어 모니터링 시스템에 관한 연구가 활발히 진행되고 있다. 라이프 케어 모니터링 시스템은 개인의 특성을 고려하여 맞춤형 건강관리 서비스가 이루어져야 하며 실시간으로 유지 및 관리 되어야 한다. 본 논문에서는 라이프 케어 모니터링 시스템에서 실시간 처리해야하는 태스크가 증가함에 따라 마감시간 준수율이 하락하는 문제점을 해결하는 방안에 관한 연구이다. 즉, 개인의 상태가 고려된 모니터링 요소에 가중치를 부여하고, 상대적으로 중요도가 떨어지는 모니터링 요소는 주기를 증가시키는 방식과 중요도에 비하여 모니터링 자원 낭비가 최대인 모니터링의 주기를 증가시키는 방식을 비교분석하여 실시간 처리율을 향상시키는 것이다. 제안한 방법의 유용성을 검증하기 위해 성능을 평가한 결과 기존 방식에 비해 최대 29%까지 마감시간 준수율이 향상됨을 확인했다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.88-95
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• 2004

The previous disk scheduling schemes for best-effort applications do not guarantee the real-time requirement of multimedia objects and the real-time disk scheduling schemes do not satisfy throughput of multimedia server. So, this paper propose a two-step disk scheduling scheme to satisfy the requirement of best-effort as well as soft real-time applications. This scheme is based on the round robin algorithm that imposes different weights on the best-effort task and the real-time one. The experiment results on the Linux kernel have shown that both best-effort tasks and real-time tasks could get fair service.

• The KIPS Transactions:PartA
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• v.16A no.6
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• pp.437-442
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• 2009

For multiprocessor systems, Earliest Deadline First (EDF) based on deadline and Least Laxity First (LLF) based on laxity are not suitable for practical environment since EDF has low schedulability and LLF has high context switching overhead. As a combining of EDF and LLF to improve the performance, Earliest Deadline Zero Laxity (EDZL) was proposed. EDZL is basically the same as EDF. But if the laxity of a task becomes zero, its priority is promoted to the highest level. In this paper, we propose Least Laxity Zero Laxity (LLZL) which is based on LLF. But context switching is allowed only if the laxity of a task on rady queue becomes zero. Simulation results show that LLZL has high schedulability approaching to LLF and low context switching overhead similar to EDF. In comparison with EDZL, LLZL has better performance in both of schedulability and context switching overhead.

• Journal of Korea Multimedia Society
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• v.14 no.11
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• pp.1478-1490
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• 2011

Recently, multi-core processors have been drawing significant interest from the embedded systems research and industry communities due mainly to their potential for achieving high performance and fault-tolerance at low cost in such products as automobiles and cell phones. To process multimedia data, a scheduling algorithm is required to meet timing constraints of periodic tasks in the system. Though Pfair scheduling algorithm can meet all the timing constraints while achieving 100% utilization on multi-core based system theoretically, however, the algorithm incurs high scheduling overheads including frequent core migrations and system-wide synchronizations. To mitigate the problems, we propose a real-time scheduling algorithm for multi-core based system so that system-wide scheduling is performed only when it is absolutely necessary. Otherwise the proposed algorithm performs scheduling within each core independently. The experimental results by extensive simulations show that the proposed algorithm dramatically reduces the scheduling overheads up to as negligible one when the utilization is under 80%.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.1
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• pp.52-57
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• 2014

This paper presents an implementation of a smooth path planning method considering physical limits on a real time operating system for a two-wheel mobile robot. A Bezier curve is utilized to make a smooth path considering a robot's position and direction angle through the defined path. A convolution operator is used to generate the center velocity trajectory to travel the distance of the planned path while satisfying the physical limits. The joint space velocity is computed to drive the two-wheel mobile robot from the center velocity. Trajectory planning, velocity command according to the planned trajectory, and monitoring of encoder data are implemented with a multi-tasking system. And the synchronization of tasks is performed with a real-time mechanism of Event Flag. A real time system with multi-tasks is implemented and the result is compared with a non-real-time system in terms of path tracking to the designed path. The result shows the usefulness of a real-time multi-tasking system to the control system which requires real-time features.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.2
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• pp.175-185
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• 2005

The scheduling methods of the distributed real-time systems have been proposed. However, they have some weak points. They did not schedule both sporadic and periodic tasks and messages at the same time or did not consider the end-to-end constraints such as precedence relations between sporadic tasks. This means that system scheduling must guarantee the constraints of practical systems and be applicable to them. This paper proposes a new scheduling method that can be applied to more practical model of distributed real-time systems. System model consists of sporadic and periodic tasks with precedence relations and sporadic and periodic messages and has end-to-end constraints. The proposed method is based on a binary search-based period assignment algorithm, an end-to-end laxity-based priority assignment algorithm, and three kinds of schedulability analysis, node, network, and end-to-end schedulability analysis. In addition, this paper describes the application model of sporadic tasks with precedence constraints in a distributed real-time system, shows that existing scheduling methods such as Rate Monotonic scheduling are not proper to be applied to the system having sporadic tasks with precedence constraints, and proposes an end-to-end laxity-based priority assignment algorithm.

• IEMEK Journal of Embedded Systems and Applications
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• v.6 no.2
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• pp.55-61
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• 2011

We propose power-saving real-time scheduling method for mixed task sets which consist of both time-based periodic and event-based aperiodic tasks in the automotive operating system. In this system, we have to pursue maximization of power-saving using the slack time estimation and minimization of response time of aperiodic tasks simultaneously. However, since these two goals conflict each other, one has to make a compromise between them according to the given application domain. In this paper, we find the adjustment factor which gives better response time of aperiodic tasks with slight power consumption increase. The adjustment factor denotes the gravity of response time for aperiodic tasks. We apply the ccEDF scheduling for time-based periodic tasks and then calculate new utilization to be applied to the adjustment factor. In this paper, we suggest the lccEDF algorithm to make a tradeoff between the two goals by systematically adjusting the factor. Simulation results show that our approach is excellent for variety of task sets.

• Proceedings of the Korea Contents Association Conference
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• 2010.05a
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• pp.353-355
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• 2010

라이프 케어 모니터링 시스템은 무자각, 진료, 일상 모니터링의 세 가지 영역으로 구성되며, 개인의 특성을 고려하여 맞춤형 건강 관리 서비스가 이루어져야 하며 실시간으로 유지 및 관리 되어야 한다. 본 논문에서는 라이프 케어 모니터링 시스템에서 실시간 처리해야하는 태스크가 증가함에 따라 마감시간 준수율이 하락하는 문제점을 해결하는 방안에 관한 연구이다. 즉, 개인의 질병과 몸 상태가 고려된 모니터링 요소에 가중치를 부여하고, 상대적으로 중요도가 떨어지는 모니터링 요소는 주기를 증가시킴으로써 실시간 처리율을 향상시키는 것이다. 제안한 방법의 유용성을 검증하기 위해 성능을 평가한 결과 기존 방식에 비해 최대 23%까지 마감시간 준수율이 향상됨을 확인했다.