• Journal of Computing Science and Engineering
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• v.11 no.2
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• pp.58-68
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• 2017

While graphics processing units (GPUs) can be used to improve the performance of real-time embedded applications that require high throughput, it is challenging to estimate the worst-case execution time (WCET) of GPU programs, because modern GPUs are designed for improving the average-case performance rather than time predictability. In this paper, a reordering framework is proposed to regulate the access to the GPU data cache, which helps to improve the accuracy of the estimation of GPU L1 data cache miss rate with low performance overhead. Also, with the improved cache miss rate estimation, tighter WCET estimations can be achieved for GPU programs.

• Journal of KIISE:Computing Practices and Letters
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• v.13 no.5
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• pp.271-281
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• 2007

Real-time support of embedded OS is not optional, but essential in contemporary embedded systems. In order to achieve these system#s real-time property, it is crucial that schedulability analysis for tasks having its property have been accomplished before system execution. Acquiring Worst-Case Execution Time(WCET) of task is a core part of schedulability analysis. Because traditional WCET tools analyze only its estimation of application task(i.e. program), it is not considered that application tasks are affected by scheduling primitives(e.g. scheduler, interrupt service routine, etc.) of OS when it schedules them. In this paper, we design and implement WCET analysis tool which deliberates on scheduling primitives of system using embedded Linux widely used in embedded OSes. This tool can estimate either WCET of normal application programs or corresponding primitives which have an influence on schduling property in embedded Linux kernel. Therefore, precision of estimation about schedulability analysis is improved. We develop this tool as Eclipse#s plug-in to work properly in any platform and support convenient interface or functionality for user.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10b
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• pp.340-342
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• 2004

인공위성과 원자력발전소와 같은 안전필수시스템의 경우, 각 작업이 주기 안에 완료되어야 하는 실시간적 특성을 가진다. 시스템이 이와 같은 요구사항을 만족하는가를 판단하기 위해서는 프로그램의 최장수행시간을 분석하는 것이 필수적이다 본 논문에서는 프로그램을 직접 실행하지 않고 최장수행시간을 분석하기 위해 구현한 Time bounder 도구를 소개하며, 다목적실용위성 2호에 탑재되는 프로그램을 대상으로 수행한 실험 결과를 분석한다.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.114-120
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• 2002

In a distributed real-time control system, it is essential to confirm the timing behavior of all tasks because these tasks of each real-time controller have to finish their processes within the specified time intervals called a deadline. In order to satisfy this objective, the timing analysis of a distributed real-time system such as shcedulability test must be performed during the system design phase. In this study, a simple application of CAN fur a vehicle body network system is formulated to apply to a holistic scheduling analysis, and the worst-case execution time (WCET) and the worst-case end-to-end response time (WCRT) are evaluated in the point of holistic system view.

• Journal of Computing Science and Engineering
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• v.3 no.1
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• pp.59-71
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• 2009

While the average-case performance is important for general-purpose applications, worst-case performance is crucial for real-time systems to ensure schedulability and reliability. Recent work has shown that simple prefetching techniques such as the Next-N-Line prefetching can benefit both average-case and worst-case performance; however, the improvement on the worstcase execution time (WCET) is rather limited and inefficient. This paper presents two instruction prefetching approaches that are specially designed to enhance the worst-case performance, including the loop-based prefetching and WCET-oriented prefetching. Our experiments indicate that both instruction prefetching techniques can achieve better worst-case execution cycles than the Next-N-Line prefetching while having various impacts on the average-case performance.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.05a
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• pp.1265-1266
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• 2005

• The Transactions of the Korea Information Processing Society
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• v.7 no.7
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• pp.2204-2218
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• 2000

This paper proposes a dynamic storage allocation algorithm, QHF(quick-half-fit) for real-time systems. The proposed algorithm manages a free block list per each worked size for memory requests of small size, and a free block list per each power of 2 size for memory requests of large size. This algorithms uses the exact-fit policy for small sie requests and provides high memory utilization. The proposed algorithm also has the time complexity O(I) and enables us to easily estimate the worst case execution time (WCET). In order to confirm efficiency of the proposed algorithm, we compare he memory utilization of proposed algorithm with that of half-fit and binary buddy system that have also time complexity O(I). The simulation result shows that the proposed algorithm guarantees the constant WCET regardless of the system memory size and provides lower fragmentation ratio and allocation failure ratio thant other two algorithms.

• Journal of Computing Science and Engineering
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• v.3 no.4
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• pp.195-215
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• 2009

Worst-case execution time (WCET) analysis is critical for hard real-time systems to ensure that different tasks can meet their respective deadlines. While significant progress has been made for WCET analysis of instruction caches, the data cache timing analysis, especially for set-associative data caches, is rather limited. This paper proposes an approach to safely and tightly bounding data cache performance by computing the worst-case stack distance of data cache accesses. Our approach can not only be applied to direct-mapped caches, but also be used for set-associative or even fully-associative caches without increasing the complexity of analysis. Moreover, the proposed approach can statically categorize worst-case data cache misses into cold, conflict, and capacity misses, which can provide useful insights for designers to enhance the worst-case data cache performance. Our evaluation shows that the proposed data cache timing analysis technique can safely and accurately estimate the worst-case data cache performance, and the overestimation as compared to the observed worst-case data cache misses is within 1% on average.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10B
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• pp.1648-1664
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• 2000

This paper proposes a real-time dynamic storage allocation algorithm QSHF(quick-segregated-half-fit) that provides various memory allocation policies. that manages a free block list per each word size for memory requests of small size good(segregated)-fit policy that manages a free list per proper range size for medium size requests and half-fit policy that manages a free list per proper range size for medium size requests and half-fit policy that manages a free list per each power of 2 size for large size requests. The proposed algorithm has the time complexit O(1) and makes us able to easily estimate the worst case execution time(WCET). This paper also suggests two algorithm that finds the proper free list for the requested memory size in predictable time and if the found list is empty then finds next available non-empty free list in fixed time. In order to confirm efficiency of the proposed algorithm we simulated the memory utilization of each memory allocation policy. The simulation result showed that each policy guarantees the constant WCET regardless of memory size but they have trade-off between memory utilization and list management overhead.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.4
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• pp.304-308
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• 2009

This paper presents the deadline driven CPU-Power management scheme for the Real-Time Embedded OS: named TMO-eCos. It used the scheduling scenarios generated by a task serialization technique for hard real- time TMO system. The serializer does a off-line analysis at design time with period, deadline and WCET of periodic tasks. Finally, TMO-eCos kernel controls the CPU speed to save the power consumption under the condition that periodic tasks do not violate deadlines. As a result, the system shows a reasonable amount of power saving. This paper presents all of these processes and test results.