• 제어로봇시스템학회논문지
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• 제18권4호
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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.

• 전기학회논문지
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• 제57권5호
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• pp.875-880
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• 2008

In this paper, a novel method to determine the optimal checkpoint interval for real-time control task is proposed considering its performance degradation according to tasks's execution time. The control task in this paper has a specific sampling period shorter than its deadline. Control performance is degraded as the control task execution time is prolonged across the sampling period and eventually zero when reached to the deadline. A new performance index is defined to represent the performance variation due to the extension of task execution time accompanying rollback fault recovery. The procedure to find the optimal checkpoint interval is addressed and several simulation examples are presented.

• International Journal of Control, Automation, and Systems
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• 제4권5호
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• pp.601-614
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• 2006

In this paper, a study on task assignment strategies for a complex real-time network system is presented. Firstly, two task assignment strategies are proposed to improve previous strategies. The proposed strategies assign tasks with meeting end-to-end real-time constraints, and also with optimizing system utilization through period modulation of the tasks. Consequently, the strategies aim at the optimizationto optimize of system performance with while still meeting real-time constraints. The proposed task assignment strategies are devised using the genetic algorithmswith heuristic real-time constraints in the generation of new populations. The strategies are differentiated by the optimization method of the two objectives-meeting end-to-end real-time constraints and optimizing system utilization: the first one has sequential genetic algorithm routines for the objectives, and the second one has one multiple objective genetic algorithm routine to find a Pareto solution. Secondly, the performances of the proposed strategies and a well-known existing task assignment strategy using the BnB(Branch and Bound) optimization are compared with one other through some simulation tests. Through the comparison of the simulation results, the most adequate task assignment strategies are proposed for some as system requirements-: the optimization of system utilization, the maximization of running tasktasks, and the minimization of the number of network node nodesnumber for a network system.

• 제어로봇시스템학회논문지
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• 제14권4호
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• pp.376-380
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• 2008

This paper deals with a performance analysis of real-time control systems, which engages DMR(dual modular redundancy) to detect transient errors and checkpointing technique to tolerate transient errors. Transient errors are caused by transient faults and the most significant type of errors in reliable computer systems. Transient faults are assumed to occur according to a Poisson process and to be detected by a dual modular redundant structure. In addition, an equidistant checkpointing strategy is considered. The probability of the successful task completion in a real-time control system where periodic checkpointing operations are performed during the execution of a real-time control task is derived. Numerical examples show how checkpoiniting scheme influences the probability of task completion. In addition, the result of the analysis is compared with the simulation result.

• 한국콘텐츠학회논문지
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• 제18권3호
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• pp.101-113
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• 2018

실시간으로 데이터를 획득하고 평가하는 것이 중요한 군용 점검 장비와 같은 시스템에서는 운영체제 레벨에서 실시간 처리가 가능해야 한다. 기술의 발전으로 기존 장비를 휴대용 단말로 대체하려는 요구가 있으나, 안드로이드가 적용된 휴대용 단말은 실시간성이 요구되는 시스템에 적합하지 않다. 안드로이드에서는 가비지 컬렉션을 통해 가용 메모리를 확보하는데, 이 작업이 수행되는 동안 다른 태스크가 중단되어 특정 태스크의 주기성을 보장할 수 없다. 본 논문에서는 이를 해결하기 위해 안드로이드의 가비지 컬렉션 실행을 제어하는 구조를 설계 및 구현하였다. 실시간 작업이 필요한 시간 동안 가비지 컬렉션을 제어하여 실시간 성능을 보장하며, 안드로이드에 실시간 성능 보장을 위한 RTiK을 적용하였다. 성능 평가를 위해 5ms 주기 태스크의 호출 주기를 측정하였으며, 제어 이전에는 태스크의 34.31%만 주기가 보장되었으나, 제어를 통해 98.18%의 태스크 주기가 만족되어 안드로이드에 실시간성을 제공하였다.

• 제어로봇시스템학회논문지
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• 제18권4호
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• pp.337-342
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• 2012

This paper presents performance evaluation of real-time mechanisms for real-time embedded linux. First, we presents process for implementing open-source real-time embedded linux namely RTAI and Xenomai. These are real-time extensions to linux kernel and we implemented real-time embedded linux over the latest linux kernel. Measurements of executions of real-time mechanisms for each distribution are performed to give a quantitative comparison. Performance evaluations are conducted in kernel space about repeatability of periodic task, response time of Semaphore, FIFO, Mailbox and Message queue in terms of inter-task communication for each distribution. These rules can be helpful for deciding which real-time linux extension should be used with respect to the requirements of the real-time applications.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.141-142
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• 2006

In this paper, DSPOCS(Digital Switchgear Panel Operation and Control Solution) is designed, which is the intelligent inference operation and control solution of substation based on IED. DSPOCS is designed as a scheduled monitoring and control task and a real-time alarm inference task, and is interlinked with BRES in the required case. The intelligent alarm inference task consists of the alarm knowledge generation part and the real-time pattern matching part The alarm knowledge generation part generates automatically alarm knowledge from DB and saves it in alarm KB. On the other hand, the pattern matching part inferences the real-time event by comparing the real-time event information furnished from IEDs of substation with the patterns of the saved alarm knowledge base.

• 정보과학회 컴퓨팅의 실제 논문지
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• 제23권7호
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• pp.452-457
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• 2017

리눅스는 범용 운영체제로써 다양한 스케줄러를 지원하며, 서로 다른 스케줄러가 런타임 시에 혼재하는 상황을 허용한다. 또한, 리눅스는 Control Group(cgroup)을 활용하여 데드라인 스케줄러(SCHED_DEADLINE)를 제외한 실시간(SCHED_FIFO, SCHED_RR) 및 비실시간(SCHED_NORMAL) 스케줄러 정책을 따르는 태스크들에 대해서 그룹 단위의 CPU 자원 예약을 지원한다. cgroup은 스케줄링 가능성 분석을 수행하여 예약된 CPU 자원을 최대한 보장하려고 한다. 하지만 현재 리눅스의 실시간 태스크 그룹에 대한 스케줄링 가능성 분석은 데드라인 태스크와 실시간 태스크를 구분하지 못하는 문제에 의해서 두 스케줄러를 사용하는 태스크가 혼재할 때 실시간 태스크 그룹의 자원예약을 거부하는 경우가 발생한다. 본 논문은 리눅스 cgroup의 실시간 태스크 그룹에 대한 스케줄링 가능성 분석에서 발생하는 문제를 분석하고, 이를 해결하는 커널 패치를 제안한다.

• 제어로봇시스템학회논문지
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• 제5권2호
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• pp.145-150
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• 1999

A real-time control system, composed of the controlled processor and the controller computer(s), may have a variety of task types, some of which have tight timing-constraints in generating the correct control input. The maximum period of those task failures tolerable by the system is called the hard deadline, which depends on not only fault characteristics but also task characteristics. In the paper, we extend a method deriving the hard deadline in LTI system executing single task. An algorithm to combine the deadlines of all the elementary tasks in the same operation-mode is proposed to derive the hard deadline of the entire system. For the end, we modify the state equation for the task to capture the effects of task failures (delays in producing correct values) and inter-correlation. We also classify the type of executing the tasks according to operation modes associated with relative importance of correlated levels among tasks, into series, parallel, and cascade modes. Some examples are presented to demonstrate the effectiveness of the proposed methods.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1986년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 17-18 Oct. 1986
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• pp.518-526
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• 1986

This paper gives the detail of the work carried out to develop real-time control software for Flexible Manufacturing Systems. A basic design philosophy to implement such software is proposed. The major features are the partitioning of complicated control actions into simplified ones, structured programming and multi-threaded transaction-based tasks. The software operates on the basis of passing task-to-task messages via mailboxes, causing appropriate actions to be taken by each task. Each task represents a separate subprocess so that the subprocesses can be run simultaneously. The task-to-task message could be easily replaced by computer-to-computer communication, using LAN, demonstrating that the software methods developed produce a flexible designs for control software of an FMS. A method of linking such software to simulation software is suggested as a potentially powerful additional design-tool.