摘要
随着计算机,网络和通信技术地发展,实时系统越来越多得被应用于工业控制、网络通信、实时监控,多媒体等领域。这些新的实时网络应用得出现给实时系统地发展提出了新的要求和挑战。
弱硬实时概念的提出,丰富和扩充了实时系统理论,也满足了实时网络应用的理论需求。弱硬实时相关问题也因此成为当前实时研究的重点问题之一。本论文的研究内容集中在弱硬实时约束规范,基于弱硬实时约束规范的调度算法及相关实验。
弱硬实时理论能够统一描述原有各类实时系统,硬实时、软实时系统都是一类典型的弱硬实时系统。本文提出了一种新的弱硬实时规范约束。从典型弱硬实时的角度分析了总线协议的实时特性,并具体针对弱硬实时调度算法DBP,讨论其在优先级设置及调度中的问题,并给出修正策略。论文还讨论了弱硬实时系统的可扩展问题,提出了任务流归类的方法。完成的相关主要工作具体的包括了以下几个方面:
1.简单回顾了实时系统的发展及其相关调度算法。
2.提出了((?),p)约束,研究了其与现有弱硬实时约束之间的关系;同时修正了文献[61]中的一个约束强弱比较的定理;全面总结了弱硬实时系统的静态调度算法和静态调度中的两个主要问题,以及动态弱硬实时调度算法及其性能评价方法等。
3.从典型弱硬实时—硬实时的角度,分析工业网络FF的MAC层任务的WCET,提出协议改进策略,并通过仿真验证了改进协议的有效性。比较了集中控制式总线协议FF和WorldFIP非周期任务调度的带宽利用率。
4.研究了DBP算法忽略状态所包含0/1信息分布的缺点,提出了与进入失效距离对称的概念—退出失效距离,并说明了改进优先级算法设置的合理性,扩展了DBP算法的优先级类别。
5.研究DBP算法在优先级设置时仅考虑该任务流本身的历史状态,而忽略任务流任务时间参数特性的缺点;提出了在任务优先级设置过程中考虑不同任务流之间任务时间参数特性的矩阵DBP算法,并给出了矩阵元素的计算公式。
With technical development of computer, network and communication, real-time systems are applied to the fields of automatic control, network communication, real-time monitor, multimedia. New requirements and challenges arise from these applications.The concept of weakly hard real-time is presented, which not only enriches and extends the classical theory of real-time system, but also meets new requirements and challenges. So related issues on weakly hard real-time are becoming hot research point nowadays. The content of thesis will focus on constraint specification of weakly hard real-time, scheduling algorithms based on weakly hard real-time and related experiments.The theory of weakly hard real-time can describe different real-time system, both hard real-time and soft real-time system are the typical weakly hard real-time systems. In this thesis, a new specification of weakly hard real-time is proposed; Real-time characteristic of fieldbus is analyzed from the viewpoint of weakly hard real-time, and improved algorithms are put forward to correct drawbacks of DBP in the process of its priority assignment. Furthermore, the problem of scalability in weakly hard real-time system is discussed, and schemes for classifying streams are proposed. The main detail research works in the thesis can be described as follows:1. Review in brief the development of real-time system and its scheduling algorithms;2. Propose ((m|—),p) constraint, and study the relationship with existing weakly hard real-time constraint; correct the theory of stringency compare in reference [61]; summarize fully the static scheduling algorithms and their main two primary problems for weakly hard real-time, and dynamic scheduling algorithms including their metric of performance evaluation;3. Analyze the WCET of MAC in FF from viewpoint of weakly hard real-time, and propose an improved scheme and validate the effectiveness by simulation; compare the bandwidth utilization of aperiodic task scheduling in centralized control like FF and WorldFIP;
4. Point out the drawback of DBP, which neglects the distribution of 0/1 information in state, and propose a distance to exit to failure state, which is symmetrical notion with distance to fall into failure state; The rationality of priority assignment is explained, and the priority number is extended;5. Improve DBP by a matrix, which takes into account timing characteristics of stream like period, deadline, service time et.al and its relationship with other streams sharing the same server; The idea remedies original DBP that only considers recent history state of stream itself; The equation is given to compute element of Matrix;6. Study the problems of scalability under the limited resource in weakly hard realtime system。 Static loss-rate balance and dynamic stream number balance class selecting algorithms are designed based on multiplex queue.7. Design two different experiment project based on diverse hardwares to validate the weakly hard real-time QoS that is provided by different real-time scheduling algorithms.Finally, some concluding remarks are given, and the future research works are pointed out.
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