• ETRI Journal
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• v.32 no.1
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• pp.84-92
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• 2010

This paper proposes the semaphore authority management (SAM) controller to optimize the dual-port SDRAM (DPSDRAM) in the mobile multimedia systems. Recently, the DPSDRAM with a shared bank enabling the exchange of data between two processors at high speed has been developed for mobile multimedia systems based on dual-processors. However, the latency of DPSDRAM caused by the semaphore for preventing the access contention at the shared bank slows down the data transfer rate and reduces the memory bandwidth. The methodology of SAM increases the data transfer rate by minimizing the semaphore latency. The SAM prevents the latency of reading the semaphore register of DPSDRAM, and reduces the latency of waiting for the authority of the shared bank to be changed. It also reduces the number of authority requests and the number of times authority changes. The experimental results using a 1 Gb DPSDRAM (OneDRAM) with the SAM controllers at 66 MHz show 1.6 times improvement of the data transfer rate between two processors compared with the traditional controller. In addition, the SAM shows bandwidth enhancement of up to 38% for port A and 31% for port B compared with the traditional controller.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.922-924
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• 2005

실시간 시스템의 개발 및 운영에 사용되는 실시간 운영체제는 여러 개의 태스크가 동시에 작업할 수 있는 멀티태스킹 환경과 각 태스크에 우선순위를 부여하여 가장 높은 우선순위의 태스크가 CPU 를 선점하는 스케줄링 방법, 그리고 태스크간 동기화 및 통신을 위한 메커니즘을 제공하고 있다. 또한 여러 태스크들에 의해 사용되는 공유자원을 관리하기 위해 세마포어(Semaphore)를 사용하여 태스크간 동기화를 제공한다. 그러나 하나의 태스크가 세마포어를 이용하여 공유자원에 대해 여러 번 접근 할 경우, 데드락(Deadlock)을 일으킬 소지가 많다. 본 논문에서는 실시간 운영체제인 $iRTOS^{TM}$ 에서 데드락을 방지하기 위한 재귀적 세마포어(Recursive Semaphore)를 설계 및 구현하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.4
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• pp.382-395
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• 1991

A general purpose distributed processes communication control mechanism is a typical approach used for synchronizing concurrent processes involved in communication. The mechanism can provide a framework on which the layered communication architectures and protocols are efficiently implemented. The mechanism is realized under restricted environment where monitor facility is not available by means of simulation using semaphore.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.443-445
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• 2002

In this paper, we present a novel efficient semaphore implementation scheme which diminishes completion time of high priority tasks and improves reliability of a system. The real-time system is constrained to complete their tasks in time. Especially, the task of a hard real-time system must meet its deadline under unfavorable conditions. In this paper, the number and sort of the locked semaphores, when an event occurred, decide whether the context switch should occur or not, so higher priority tasks diminish in their completion time. The experimental results show that the proposed method gives performance improvements in finish time of high priority tasks of about 11% over the Zuberi.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04a
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• pp.687-690
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• 2002

In this paper, we present a novel semaphore implementation scheme which shortens finish time of high priority tasks and improves reliability of a system. The real-time systems have time constraints. Especially, the task with hard real-time constraints must meet its deadline. Consequently, managing shared resources is considered guaranteeing mutual exclusion as well as meeting task's deadline under unfavorable condition. According to the number and sort of the locked semaphores under the event occurred, this paper presents the reduction of the finish time of high priority task by decision whether the context switched or not. The experimental results show that the proposed method gives performance improvements in finish time of high priority tasks of about 11% over zuberi[4] method.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11a
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• pp.555-558
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• 2002

실시간 시스템의 개발 및 운영에 사용되는 실시간 운영체제는 여러 개의 태스크가 동시에 작업할 수 있는 멀티태스킹 환경과 각 태스크에 우선순위를 부여하여 가장 높은 우선순위의 태스크가 CPU 를 선점하는 스케줄링 방법, 태스크간 동기화 및 통신을 위한 메커니즘을 제공하고 있다. 그리고 여러 태스크들에 의해 사용되는 공유자원을 관리하기 위해 세마포어를 사용하여 태스크간에 동기화를 제공한다. 하지만 세마포어만으로 공유자원을 관리하게 되면 더 높은 우선순위의 태스크가 실행 준비 되어 있음에도 불구하고 상대적으로 낮은 우선순위의 태스크가 CPU 를 선점하는 우선순위 역전이 발생하여 실시간 운영체제의 핵심인 시간 결정성을 만족하지 못해 시스템에 심각한 문제를 발생 시킬 수 있다. 본 논문에서는 실시간 운영체제인 $iRTOS^{TM}$에서 우선순위 역전을 예방하기 위한 방법중 하나인 Priority Ceiling Protocol을 이용한 Mutual Exclusion Semaphore를 설계하고 구현한 내용을 기술한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.1-9
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• 2016

Train control systems have changed from wayside electricity-centric to onboard communications-centric. The latest train control system, the CBTC system, has high efficiency for interval control based on two-way radio communications between the onboard and wayside systems. However, since the wayside system is the center of control, the number of input trains to allow a wayside system is limited, and due to the cyclic-path control flows between onboard and wayside systems, headway improvement is limited. In this paper, we propose a train interval-control and train-centric distributed interlocking algorithm for an autonomous train-driving control system. Because an autonomous train-driving control system performs interval and branch control onboard, both tracks and switches are shared resources as well as semaphore elements. The proposed autonomous train-driving control performs train interval control via direct communication between trains or between trains and track-side apparatus, instead of relying on control commands from ground control systems. The proposed interlocking algorithm newly defines the semaphore scheme using a unique key for the shared resource, and a switch that is not accessed at the same time by the interlocking system within each train. The simulated results show the proposed autonomous train-driving control system improves interval control performance, and safe train control is possible with a simplified interlocking algorithm by comparing the proposed train-centric distributed interlocking algorithm and various types of interlock logic performed in existing interlocking systems.

• 제어로봇시스템학회:학술대회논문집
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• 1989.10a
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• pp.520-523
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• 1989

MAP(Manufacturing Automation Protocol), Network Protocol for FA has 7 Layer Structure of OSI. Being an Application Layer Protocol for Communication Interfaced with the Actual Programmable Devices, MMS(Manufacturing Message Specification) Consists of Three Factors of Services, Interfaces, and Protocol. For Details, It Classifies with the Followings ; Connection/Context Management, Remote Variable Access, Semaphore Management, File transfer and Management, Program UP/DOWN Load, Remote Program Fxecution. In this Paper Designing MAP Network Station of Programmable Device, we Analyze the Protocol of MMS, and Realize the State Diagram of each Services and Propose the Model of MMS Function Call Instructions.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04a
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• pp.199-201
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• 2003

실시간 운영체제(Real-Time OS)는 우선순위 기반의 선점형 스케줄링을 제공하는 운영체제로서 시간 결정성 (Determinism)을 보장하는 특징이 있다. 그러나, 우선순위가 높은 태스크가 우선순위가 낮은 태스크에 의해 CPU를 점유 당하는 우선순위 역전(Priority Inversion)이 발생하여 시간 결정성이 보장되지 못하면 시스템의 심각한 결함을 야기할 수 있다. 본 논문에서는 우선순위 역전을 해결하기 위하여 Priority Inheritance Protocol 을 적용한 세마포 (Semaphore)의 구현에 대해 기술한다.

• The Journal of Korea Robotics Society
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• v.7 no.4
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• pp.292-298
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• 2012

It is a real-time system that the system correctness depends not only on the correctness of the logical result of the computation but also on the result delivery time. Real-time Operating System (RTOS) is a software that manages the time of a microprocessor to ensure that the most important code runs first so that it is a good building block to design the real-time system. The real-time performance is achieved by using real-time mechanisms through data communication and synchronization of inter-task communication (ITC) between tasks. Therefore, test on the response time of real-time mechanisms is a good measure to predict the performance of real-time systems. This paper aims to analysis the response characteristics of real-time mechanisms in kernel space for real-time embedded Linux: RTAI and Xenomai. The performance evaluations of real-time mechanism depending on the changes of task periods are conducted. Test metrics are jitter of periodic tasks and response time of real-time mechanisms including semaphore, real-time FIFO, Mailbox and Message queue. The periodicity of tasks is relatively consistent for Xenomai but RTAI reveals smaller jitter as an average result. As for real-time mechanisms, semaphore and message transfer mechanism of Xenomai has a superior response to estimate deterministic real-time task execution. But real-time FIFO in RTAI shows faster response. The results are promising to estimate deterministic real-time task execution in implementing real-time systems using real-time embedded Linux.