Weakly Hard Real-Time System And Its Scheduling Algorithms

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.