嵌入式实时系统通信机制与优化技术研究

发布时间：2018-06-09 01:46

本文选题：实时系统 + 通信机制　；参考：《国防科学技术大学》2013年博士论文

【摘要】：近年来,嵌入式实时系统的应用已经广泛渗透到家电、工业控制、汽车、火车、航空航天等各个行业。一方面,许多原来由机械和液压完成的功能逐步被电子系统取代,各种控制系统电气化程度不断提高,另一方面,人们对系统的安全性、舒适性等功能和性能的要求越来越高。这些变化要求实时系统提供更加强大的计算能力,因此,实时系统的处理器向多核方向发展,且处理器的数量急剧增长。这就对实时系统的通信机制提出了越来越严苛的要求。本文对实时系统通信机制进行了探索和研究,并对多核任务间通信机制和实时通信网络进行了设计和优化,主要研究内容包括以下四个方面:(1)多核嵌入式实时系统任务间通信机制研究在实时系统中,任务在访问共享变量时,需要采用通信机制来保证访问的互斥性。多核体系结构本身具有高性能、低功耗等多种优势,其在实时系统领域的应用越来越广泛。由于多核结构的分布式特性,通信机制的设计变得更加复杂。目前,针对多核结构的通信机制主要包括锁机制和无等待机制两大类,然而,这两类机制在存储开销和系统可调度性方面各有优劣,无法兼顾两个指标。本文提出了一种新颖的弹性多处理器通信机制(FMCS),该机制通过一种我们提出的启发式优化算法为每个共享变量分配其最适用的通信策略和冲突处理策略,具有存储开销低和系统可调度性好的优势。FMCS机制给出了每个任务在最坏情况下的响应时间计算公式,从而能够对实时系统进行确定性的时间分析。通过实验验证,结果表明:FMCS能够在保证系统可调度性的前提下大幅度降低存储开销,且当系统利用率达到90%以上时,使用FMCS机制仍能保证系统可调度,因而FMCS具有较高的可扩展性。(2)实时通信网络的消息部署研究实时系统用于实现控制任务时,控制路径的延迟大小对控制精度影响重大,因此,要达到较高的控制精度就必须将实时系统控制路径的延迟控制在一定范围内。在基于模型的开发中,系统的延迟属性可通过对功能模型进行仿真和模型检验来提前验证。为了确保最终部署的系统仍保持系统需要的属性,在任务和通信消息实现时需要保证模型的延迟属性不变。但是,在某些情况下,完全保证模型的延迟属性不变是不可能做到的,此时,需要在模型中增加通信延迟,并重新修改模型,进行迭代设计。消息部署的延迟在模型延迟属性中占据相当大的比重,然而,目前对于基于模型开发过程中的消息部署问题的研究还十分缺乏。本文建立了一种新颖的低延迟消息部署模型(LLMD),该模型是一种基于时间触发通信机制Flex Ray调度问题的数学模型,能够在保证普通路径的延迟时限和系统的可调度性的前提下,在关键控制路径中引入尽可能少的单位延迟。最后,本文利用一个X-by-wire实例和一个主动安全实例对该模型进行了实验验证,结果表明:该模型能够在有限时间内找到消息部署优化方案,且该方案在满足系统可调度性的前提下会尽可能少的引入额外延迟。(3)实时通信网络安全机制研究随着航空电子、汽车电子等系统中联网设备的增加和电气化程度的提高,系统的可访问性急剧上升,这导致实时通信网络面临一系列严重的安全隐患。本文提出了SSS机制——一种用于实时通信网络的智能安全机制,该安全机制能够有效抵御伪造和篡改攻击,大大提高了通信系统的安全性,并允许在负载较轻的处理器上以软件方式代替原本由硬件实现的安全相关操作(签名、认证、密钥生成等),能够显著降低硬件开销。本文提出了SSS机制的优化设计模型,该模型在保证通信安全性和系统可调度性的前提下,合理安排消息、密钥和任务的调度,尽可能少的引入硬件单元,显著降低了实现成本;该模型提供多种安全级别,支持设计人员根据通信系统负载选择最佳安全级别。最后,我们使用两个工业实例对提出的SSS机制进行了实验验证,结果发现:SSS机制能够在有限的时间内找到优化方案,且与现有的Flex Ray安全机制相比,能够大大降低硬件开销。(4)实时通信网络的可扩展性研究随着嵌入式系统功能的不断增加和性能的迅速提高,实时系统中的任务越来越多,任务间的通信数据急剧增加,从而对通信网络的可扩展性提出了更高的要求。本文提出了一种高可扩展实时通信网络结构HSRN。HSRN通过在Flex Ray通信系统中引入交换机将通信系统分割成多个分支(branch),有效隔离了广播域,从而大大提高了通信系统的可扩展性。HSRN中的交换机采用了一种我们设计的消息可缓存交换结构,该交换结构允许跨分支通信消息在发送端和接收端的不同位置时间槽上传输,且即使出现两个分支的消息同时发向一个目标分支的冲突情况,也可通过输入端的缓冲队列来解决冲突,从而放松了调度约束,允许通信网络容纳更多的消息,提高了网络利用率。为了提高HSRN中各分支负载的均衡性,本文提出了一种负载均衡优化算法,该算法能够在有限时间内找到最为合理的网络分割方案,使得最大负载分支使用尽可能少的时间槽,从而保证了HSRN各分支的负载均衡,提高了实时通信网络的可扩展性。本文通过X-by-wire案例和一个合成案例对HSRN进行了实验验证,结果表明:HSRN能够在时间槽使用总数、负载均衡和交换结构最小缓存配置之间进行很好的优化,在满足网络容量的同时兼顾了负载均衡,从而具有非常高的可扩展性。综上,本文对实时系统通信机制的若干问题进行了研究,从不同角度对通信机制进行了设计和优化,提出了一系列的模型和优化设计方法,对推动实时系统通信机制的发展做出了积极的贡献,具有一定的理论意义和应用价值。
[Abstract]:In recent years, the application of embedded real-time system has been widely permeated into various industries, such as household appliances, industrial control, automobile, train, aerospace and other industries. On the one hand, many functions completed by machinery and hydraulics are gradually replaced by electronic systems, and the degree of electrification of various control systems is constantly improved. On the other hand, people are safe and comfortable for the system. The requirements of sexual function and performance are becoming higher and higher. These changes require the real-time system to provide more powerful computing power. Therefore, the processor of the real-time system develops to the multi core direction, and the number of processors is increasing rapidly. This makes the communication mechanism of real-time systems more and more stringent. This paper is a communication mechanism for real-time systems. The research and research are carried out, and the communication mechanism and real-time communication network between multi core tasks are designed and optimized. The main research contents include the following four aspects: (1) the inter task communication mechanism of multi core embedded real-time systems is studied in the real-time system. The communication mechanism is needed to ensure the mutual access when the task is access to the shared variables. The multi-core architecture itself has many advantages, such as high performance, low power consumption and so on. It has become more and more widely used in the field of real-time system. Because of the distributed characteristics of multi-core structure, the design of communication mechanism becomes more complex. At present, the communication mechanism for multi-core structure includes two main categories, lock mechanism and no wait mechanism, however, this The two types of mechanisms have advantages and disadvantages in storage overhead and system schedulability. This paper proposes a novel flexible multi processor communication mechanism (FMCS). This mechanism uses a heuristic optimization algorithm proposed by us to allocate the most applicable communication strategy and conflict processing strategy for each shared variable. The.FMCS mechanism with low storage cost and good system schedulability gives the response time calculation formula for each task in the worst case, and can make deterministic time analysis of the real-time system. The results show that FMCS can greatly reduce the storage cost under the premise of guaranteeing the system adjustable, and when the system is adjustable, the storage cost can be greatly reduced. When the system utilization ratio is above 90%, the system can still ensure the schedulability of the system using the FMCS mechanism, so FMCS has high scalability. (2) a real-time communication network message deployment research real-time system is used to realize the control task, the delay size of the control path plays a significant role in the control precision. Therefore, the higher control precision must be achieved. The delay property of the system is controlled in a certain range. In the model based development, the delay properties of the system can be verified ahead of time by simulation and model test of the function model. In order to ensure that the final deployed system still maintains the required properties of the system, the model is guaranteed to be extended when the task and communication message are implemented. However, in some cases, it is impossible to completely guarantee the delay attribute of the model. At this time, it is necessary to add communication delay in the model and revise the model for iterative design. The delay of message deployment is a large proportion of the model delay attributes. However, the current model is developed for the model based on the model. A new low delay message deployment model (LLMD) is established in this paper. This model is a mathematical model based on the scheduling problem of Flex Ray based on time triggered communication mechanism. It can control the key control path on the premise of guaranteeing the delay time limit and the schedulability of the common path. In the path, the minimum unit delay is introduced. Finally, a X-by-wire example and an active security example are used to verify the model. The results show that the model can find the optimal scheme of message deployment in a limited time, and the scheme will be introduced as little as possible to meet the schedulability of the system. (3) (3) the research on the security mechanism of real time communication network, with the increase of networking equipment and the increase of electrification in the avionics, automotive electronics and other systems, the accessibility of the system has risen sharply, which leads to a series of serious security risks in the real time communication network. This paper proposes a SSS mechanism, a kind of real-time communication network. The mechanism of intelligent security, which can effectively resist forgery and tampering attacks, greatly improves the security of the communication system, and allows software to replace the security related operations (signature, authentication, key generation, etc.) which are originally implemented by hardware in a lighter load processor, and can significantly reduce the hardware overhead. This paper proposes a SSS On the premise of guaranteeing communication security and system schedulability, the model can reasonably arrange the message, key and task scheduling under the premise of ensuring communication security and system schedulability, and reduce the cost of implementation as little as possible. This model provides a variety of security levels and supports designers to select the best security level according to the communication system load. Finally, we use two industrial examples to verify the proposed SSS mechanism. The results show that the SSS mechanism can find the optimization scheme in a limited time, and can greatly reduce the hardware overhead compared with the existing Flex Ray security mechanism. (4) the scalability of the real-time communication network is based on the function of the embedded system. Increasing and rapidly increasing performance, more and more tasks in real time systems, the rapid increase of communication data between tasks, and higher requirements for the scalability of communication networks. A high scalable real-time communication network structure, HSRN.HSRN, is introduced in this paper by introducing a switch in the Flex Ray communication system. The system is divided into multiple branches (Branch), effectively isolating the broadcast domain, thus greatly improving the scalability of the communication system's extensibility.HSRN using a message caching switch we design, which allows transmissions of cross branch communication messages to be transmitted at different locations in the sender and receiving end, even if it appears. The messages of the two branches are simultaneously sent to the conflict of a target branch and can be solved by the buffer queue of the input terminal. Thus, the scheduling constraints are relaxed, the communication network is allowed to accommodate more messages and the network utilization is improved. In order to improve the equilibrium of the branch loads in HSRN, a load balancing optimization is proposed in this paper. The algorithm can find the most reasonable network segmentation scheme in the limited time, which makes the maximum load branch use as little time slot as possible, thus ensuring the load balance of each branch of HSRN and improving the scalability of the real-time communication network. In this paper, a X-by-wire case and a synthetic case are used to verify the HSRN. The results show that HSRN can be well optimized between the total amount of time slot, load balance and the minimum buffer configuration of the switching structure. It can satisfy the network capacity while balancing the load, thus having very high scalability. In this paper, several problems of the real-time system communication mechanism are studied in this paper, from different angles. The communication mechanism is designed and optimized, and a series of models and optimal design methods are put forward. It has made a positive contribution to the development of the real-time system communication mechanism, and has certain theoretical significance and application value.
【学位授予单位】：国防科学技术大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TP332

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