• The KIPS Transactions:PartA
• /
• v.9A no.1
• /
• pp.9-18
• /
• 2002

In this paper, we propose scalable scheduling techniques based on EDF to efficiently integrate hard real-time and multimedia soft real-time tasks in the distributed real-time multimedia database system. Hard tasks are guarangteed based on worst case execution times, whereas multimedia soft tasks are served based on mean execution times. This paper describes a served-based scheme for partitioning the CPU bandwidth among different task classes that coexist in the same system. To handle the problem of class overloads characterized by varying number of tasks and varying task arrival rates, thus scheme shows how to adjust the fraction of the CPU bandwidth assigned to each class. This scheme fixes the maximum time that each hard task can execute in the period of the server, whereas it can dynamically change the bandwidth reserved to each multimedia task. The proposed method is capable of minimizing the mean tardiness of multimedia tasks, without jeopardizing the schedulability of the hard tasks. The performance of this scheduling method is compared with that of similar mechanisms through simulation experiments.

• The Korean Journal of Archival Studies
• /
• no.32
• /
• pp.127-176
• /
• 2012

Metadata is well recognized as one of the foundational factors in archiving and long-term preservation of digital resources. There are several metadata standards for records management, archives and preservation, e.g. ISAD(G), EAD, AGRkMs, PREMIS, and OAIS. Consideration is important in selecting appropriate metadata standards in order to design metadata schema that meet the requirements of a particular archival system. Interoperability of metadata with other systems should be considered in schema design. In our previous research, we have presented a feature analysis of metadata standards by identifying the primary resource lifecycle stages where each standard is applied. We have clarified that any single metadata standard cannot cover the whole records lifecycle for archiving and preservation. Through this feature analysis, we analyzed the features of metadata in the whole records lifecycle, and we clarified the relationships between the metadata standards and the stages of the lifecycle. In the previous study, more detailed analysis was left for future study. This paper proposes to analyze the metadata schemas from the viewpoint of tasks performed in the lifecycle. Metadata schemas are primarily defined to describe properties of a resource in accordance with the purposes of description, e.g. finding aids, records management, preservation and so forth. In other words, the metadata standards are resource- and purpose-centric, and the resource lifecycle is not explicitly reflected in the standards. There are no systematic methods for mapping between different metadata standards in accordance with the lifecycle. This paper proposes a method for mapping between metadata standards based on the tasks contained in the resource lifecycle. We first propose a Task Model to clarify tasks applied to resources in each stage of the lifecycle. This model is created as a task-centric model to identify features of metadata standards and to create mappings among elements of those standards. It is important to categorize the elements in order to limit the semantic scope of mapping among elements and decrease the number of combinations of elements for mapping. This paper proposes to use 5W1H (Who, What, Why, When, Where, How) model to categorize the elements. 5W1H categories are generally used for describing events, e.g. news articles. As performing a task on a resource causes an event and metadata elements are used in the event, we consider that the 5W1H categories are adequate to categorize the elements. By using these categories, we determine the features of every element of metadata standards which are AGLS, AGRkMS, PREMIS, EAD, OAIS and an attribute set extracted from DPC decision flow. Then, we perform the element mapping between the standards, and find the relationships between the standards. In this study, we defined a set of terms for each of 5W1H categories, which typically appear in the definition of an element, and used those terms to categorize the elements. For example, if the definition of an element includes the terms such as person and organization that mean a subject which contribute to create, modify a resource the element is categorized into the Who category. A single element can be categorized into one or more 5W1H categories. Thus, we categorized every element of the metadata standards using the 5W1H model, and then, we carried out mapping among the elements in each category. We conclude that the Task Model provides a new viewpoint for metadata schemas and is useful to help us understand the features of metadata standards for records management and archives. The 5W1H model, which is defined based on the Task Model, provides us a core set of categories to semantically classify metadata elements from the viewpoint of an event caused by a task.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.10
• /
• pp.2760-2765
• /
• 2009

Pfair scheduling algorithm, which is an optimal scheduling algorithm in the hard real-time multiprocessor environments, is based on the fixed quantum size. Recently, several methods that determine the maximum quantum size dynamically were proposed in the mode change environments. But these methods considered the case in which the period of a task can only be decreased. In this paper, we consider the case in which the period of a task can be decreased or increased, and propose an improved method that determine the maximum quantum size dynamically in the mode change environments. A simulation shows that the proposed method is effective.

• Proceedings of the Korean Information Science Society Conference
• /
• 2000.04a
• /
• pp.95-97
• /
• 2000

자바는 플랫폼 독립성, 보안, 멀티 쓰레드 지원, 가베지 콜렉터 등 많은 장점을 갖고 있는 언어이다. 하지만 현재의 자바 가상 기계(JVM)는 시간 제약 조건을 갖는 주기적인 태스크 수행, 실시간 스케쥴링 등 실시간 응용을 위한 지원이 미흡한 실정이다. 본 논문에서는 실시간 운영체제인 VxWorks와 내장형 JVM인 퍼스널 자바 상에서 실시간 응용 프로그램의 지원을 위한 자바 쓰레드를 설계, 구현한다. 이를 위해 기존의 자바 쓰레드에 시작시간, 주기, 종료시한 등의 시간 속성을 삽입하고, 실시간 자바 쓰레드 API 클래스를 구현한다. 실시간 스케쥴러를 세가지 방식으로 구현한다. 첫째는, JVM을 수정하지 않고 시간 속성에 따라 쓰레드에 우선 순위를 할당하여 스케쥴링하는 방식이고, 둘째는 JVM을 수정하여 시간 속성에 따라 VxWorks 커널 스케쥴러를 통해 스케쥴링하는 방식이며, 셋째는 독립적인 스케쥴링 태스크를 구현하는 방식이다. 쓰레드 생성, 문맥 교환 등의 오버헤드와 스케쥴링 시 종료시한 초과 비율 등의 기준을 통해 각각의 성능을 비교한 결과, VxWorks 커널 스케쥴러를 이용한 방식이 가장 적합하다는 결론을 얻을 수 있었다.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2005.11a
• /
• pp.1445-1448
• /
• 2005

실시간 시스템은 높은 수준의 안정성을 요구하는 시스템이다. 실시간 시스템에서 오류는 잘못된 응답 뿐만 아니라 시간적으로 늦은 응답도 오류를 발생 시킬 수 있다. 따라서 실시간 시스템의 안정성을 보장해 주기 위해서 실시간 태스크의 시간 제약에 대한 모니터링 및 오류발생 시에 오류를 처리해 줄 수 있는 기법이 필요하다. 본 논문은 Timed Conformance Monitor를 통해서 실시간 태스크가 시간의 제약을 만족하는지를 분석하고 또한 분석 결과에 따라 오류를 처리할 수 있는 Fault Handler를 추가하여 실시간 시스템에 대한 Fault Tolerance를 보장해 줄 수 있는 기법을 제시한다.

• Journal of Korea Multimedia Society
• /
• v.14 no.11
• /
• pp.1478-1490
• /
• 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
• /
• v.24 no.1
• /
• pp.52-57
• /
• 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 KIISE:Computing Practices and Letters
• /
• v.8 no.2
• /
• pp.174-182
• /
• 2002

The object-oriented design methods and their CASE tools are widely used in practice by many real-time software developers. However, object-oriented CASE tools require an additional step of identifying tasks from a given design model. Unfortunately, it is difficult to automate this step for a couple of reasons: (1) there are inherent discrepancies between objects and tasks; and (2) it is hard to derive tasks while maximizing real-time schedulability since this problem makes a non-trivial optimization problem. As a result, in practical object-oriented CASE tools, task identification is usually performed in an ad-hoc manner using hints provided by human designers. In this paper, we present a systematic, schedulability-aware approach that can help mapping real-time object-oriented models to multi-threaded implementations. In our approach, a task contains a group of mutually exclusive transactions that may possess different periods and deadline. For this new task model, we provide a new schedulability analysis algorithm. We also show how the run-time system is implemented and how executable code is generated in our frame work. We have performed a case study. It shows the difficulty of task derivation problem and the utility of the automated synthesis of implementations as well as the Inappropriateness of the single-threaded implementations.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2010.11a
• /
• pp.1373-1376
• /
• 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
• /
• v.8 no.1
• /
• pp.88-95
• /
• 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.