• Journal of KIISE:Computing Practices and Letters
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• v.8 no.2
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• pp.174-182
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• 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.

• 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.

• KIPS Transactions on Computer and Communication Systems
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• v.6 no.12
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• pp.479-486
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• 2017

Volunteer computing is a new computing paradigm that performs operations on idle resources of many nodes. The operation method of the client application for the execution of the volunteer computing is determined by the setting information of the user. Ideal operation requires optimized settings for system features and operating methods of other applications. In this paper, we analyze the usage ratio of CPU and GPU periodically, and develop a manager that dynamically applies optimized options. Through our proposed mechanism, the performance of the task computing is higher than that of the existing Volunteer Computing, and the performance interference is minimized. It is expected that volunteers will be able to provide higher computing resources for Volunteer Computing Project.

• 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.

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

• Proceedings of the Korea Inteligent Information System Society Conference
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• 2007.11a
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• pp.329-334
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• 2007

감시정찰 센서네트워크의 모든 센서노드 및 싱크노드들은 한정된 자원과 저사양의 하드웨어로 동작하며, 각 침입탐지 센서들이 수집한 상황 데이터를 신뢰성 있게 전송할 수 있어야 한다. 본 초소형 내장소프트웨어는 이러한 감시정찰 센서네트워크의 특성에 맞게 설계되어 센서 및 싱크노드에 탑재될 수 있는 소프트웨어로서, 센서 OS 커널, 센서미들웨어, 보안커널로 구성된다. 센서 OS는 Multithread 기반으로 실시간, 비실시간 태스크를 위한 각기 다른 스케줄링 방식을 제공하며 지연된 인터럽트 처리 기능, 주기적 태스킹 기능과 효율적 에너지 관리 기능을 제공하여 센서 네트워크에 특화된 어플리케이션 개발을 용이하게끔 한다. 또한 센서미들웨어는 OS 커널과 어플리케이션 사이에 존재하여 위치인식, 시간동기, 네트워크 관리, 원격 업데이트 기능 등 어플리케이션에서 공통적으로 요구하는 필수 기능들을 제공한다.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.8
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• pp.594-601
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• 2004

We analyze checkpoint strategy for multiple real-time periodic tasks with hard deadlines. Real-time tasks usually have deadlines associated with them. For multiple real-time tasks, checkpoint strategy considering deadlines of all tasks is very difficult to derive. We analyze the problem of checkpoint placement for such multiple periodic tasks. In our strategy, the interval between checkpoints is determined for each task considering its deadline. An approximated failure probability over a specified interval is derived. Then the number of checkpoints for each task is selected to minimize the approximated failure probability. To show the usefulness of our strategy, error bound between the exact and the approximated failure probability is estimated, which is revealed to be quite small.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.677-680
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• 2011

Error detection and correcting codes are typically used to protect against soft errors. In addition, scrubbing is applied which is a fundamental technique to avoid the accumulation of soft errors. This paper introduces an optimal scrubbing scheme, which is suitable for a system with auto error detection and correction logic. An auto error detection and correction logic can correct soft errors without CPU's writing operation. The proposed scrubbing scheme leads to maximum reliability by considering both allowable scrubbing load and the periodic accesses to memory by the tasks running in the system.

• KIISE Transactions on Computing Practices
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• v.22 no.1
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• pp.1-7
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• 2016

When multiple applications are running concurrently on a multi-processor system, interferences between applications make it difficult to guarantee real-time constraints. We propose a novel interference analysis technique that allows sharing of share processors among dataflow applications, while satisfying real-time constraints. Based on the interference analysis, we develop a co-scheduling technique that aims to minimize the resource usage. Compared to an existent technique that involves converting application graphs to real-time tasks, the proposed technique shows better results in terms of resource usage, especially when it is applied to applications with tight time constraints.

• The Journal of the Korea Contents Association
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• v.17 no.10
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• pp.587-597
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• 2017

Recently, the demand for real-time performance in mobile environment is increasing due to the improvement of hardware performance, however a GPOS(General-Purpose Operating System) such as Android and Linux do not provide real-time performance. We developed RTiK(Real-Time implant Kernel) for this problem, but it has the disadvantage of supporting only x86 Architecture. In this paper, we designed and implemented a RTiKA(Real-Time implanted Kernel for ARM) to support real-time in ARM Linux. We used MCT(Multi-Core Timer) timer which replaces Local APIC Timer for real-time support, and we measured the period of generated real-time task for performance verification and evaluation. As the recent the RTiKA can guarantee the operating of several real-time tasks based on the cycle of 1ms.