实时性分布嵌入式系统设计

分布嵌入式系统的应用通常具有实时性要求,其实时性需要从任务调度、通信协议、调用接口和嵌入式操作系统四个方面得到支持。采用两阶段调度策略既可以保证调用的透明性,又可以简化任务调度算法;基于优先级的线路竞争算法可以改进以太网使其符合实时性要求;采用微型Java虚拟机作为分布式中间件可以为系统调用接口提供一个统一的支持平台。     

分布式嵌入式系统实时调度的建模

针对RBTPN模型在建模分布式嵌入式系统实时调度时的不足,提出了一种新的扩展时间Petri网模型。该模型通过在需要处理器资源的变迁上引入变迁速率因子,得到具有相同优先级变迁的运行速率函数,从而在分布式嵌入式系统的调度建模中,在单个处理器上结合了固定优先级可抢先调度和轮转调度。随后给出了该模型可达图的构造方法,以便可以得到调度序列的各种性质。     

Rolling-horizon scheduling for energy constrained distributed real-time embedded systems

Energy-efficient scheduling approaches are critical to battery driven real-time embedded systems. Traditional energy-aware scheduling schemes are mainly based on the individual task scheduling. Consequently, the scheduling space for each task is small, and the schedulability and energy saving are very limited, especially when the system is heavily loaded. To remedy this problem, we propose a novel rolling-horizon (RH) strategy that can be applied to any scheduling algorithm to improve schedulability. In addition, we develop a new energy-efficient adaptive scheduling algorithm (EASA) that can adaptively adjust supply voltages according to the system workload for energy efficiency. Both the RH strategy and EASA algorithm are combined to form our scheduling approach, RH-EASA. Experimental results show that in comparison with some typical traditional scheduling schemes, RH-EASA can achieve significant energy savings while meeting most task deadlines (namely, high schedulability) for distributed real-time embedded systems with dynamic workloads.     

Modeling and analysis of scheduling for distributed real-time embedded systems

Aimed at the deficiencies of resources based time Petri nets (RBTPN) in doing scheduling analysis for distributed real-time embedded systems, the assemblage condition of complex scheduling sequences is presented to easily compute scheduling length and simplify scheduling analysis. Based on this, a new hierarchical RBTPN model is proposed. The model introduces the definition of transition border set, and represents it as an abstract transition. The abstract transition possesses all resources of the set, and has the highest priority of each resource; the execution time of abstract transition is the longest time of all possible scheduling sequences. According to the characteristics and assemblage condition of RBTPN, the refinement conditions of transition border set are given, and the conditions ensure the correction of scheduling analysis. As a result, it is easy for us to understand the scheduling model and perform scheduling analysis.     

模型驱动工程在分布式实时嵌入式系统QoS评价中的应用

在分析传统的分布式实时嵌入式系统开发过程中,针对服务质量(QoS)评价方法存在弊端的问题,总结了运用模型驱动工程(MDE)对分布式实时嵌入式系统的服务质量进行管理,将服务质量评价引入系统开发周期的各种探索,指出该方法应解决的几个关键问题,并分析了几种具有代表性解决方案的优缺点,提出了解决方法和建议.     

Communications-oriented development of component-based vehicular distributed real-time embedded systems

We propose a novel model- and component-based technique to support communications-oriented development of software for vehicular distributed real-time embedded systems. The proposed technique supports modeling of legacy nodes and communication protocols by encapsulating and abstracting the internal implementation details and protocols. It also allows modeling and performing timing analysis of the applications that contain network traffic originating from outside of the system such as vehicle-to-vehicle, vehicle-to-infrastructure, and cloud-based applications. Furthermore, we present a method to extract end-to-end timing models to support end-to-end timing analysis. We also discuss and solve the issues involved during the extraction of these models. As a proof of concept, we implement our technique in the Rubus Component Model which is used for the development of software for vehicular embedded systems by several international companies. We also conduct an application-case study to validate our approach.     

Service based meta-model for the development of distributed embedded real-time systems

The development complexity of Distributed Embedded Real-Time Systems (DERTS) can be reduced by the use of Service-Oriented Computing (SOC). However, the existing modeling methods allow modeling of either DERTS or SOC concepts and there is a lack of meta-model for Service-Oriented development of DERTS. This paper proposes a service-based meta-model for DERTS, along with the constraints of the elements of the meta-model. A Smart Home case study was designed to validate the meta-model. This meta-model could not only be beneficial for Service-Oriented development of DERTS, but can also be used at the Platform Independent Model (PIM) level of MDD.     

Problems of instrumental support for the development of distributed embedded real-time systems

Distributed embedded real-time systems (DRTESs) are classified among objects that are complex in their development and crucial in their use. The problems of Instrumental Support and automation of development of DRTESs are still actual, even after more than 40 years of research. This paper refine the notion of DRTES. The shortcomings of traditional approaches to the design of DRTESs are considered and a model-oriented approach to the design is formulated. A concept of the instrumental environment supporting this approach has been proposed. Basic problems to be addressed when building such an environment are formulated. The current state of the art in solving these problems is described.     

Scheduling for embedded real-time systems

The authors review several approaches to control-oriented and dataflow-oriented software scheduling to determine whether a given technique can satisfy deadlines, throughput, and other constraints for embedded real-time systems     

Hierarchical control of multiple resources in distributed real-time and embedded systems

Real-time and embedded systems have traditionally been designed for closed environments where operating conditions, input workloads, and resource availability are known a priori, and are subject to little or no change at runtime. There is increasing demand, however, for adaptive capabilities in distributed real-time and embedded (DRE) systems that execute in open environments where system operational conditions, input workload, and resource availability cannot be characterized accurately a priori. A challenging problem faced by researchers and developers of such systems is devising effective adaptive resource management strategies that can meet end-to-end quality of service (QoS) requirements of applications. To address key resource management challenges of open DRE systems, this paper presents the Hierarchical Distributed Resource-management Architecture (HiDRA), which provides adaptive resource management using control techniques that adapt to workload fluctuations and resource availability for both bandwidth and processor utilization simultaneously. This paper presents three contributions to research in adaptive resource management for DRE systems. First, we describe the structure and functionality of HiDRA. Second, we present an analytical model of HiDRA that formalizes its control-theoretic behavior and presents analytical assurance of system performance. Third, we evaluate the performance of HiDRA via experiments on a representative DRE system that performs real-time distributed target tracking. Our analytical and empirical results indicate that HiDRA yields predictable, stable, and efficient system performance, even in the face of changing workload and resource availability.     

Executable specifications for embedded distributed systems

Combining hardware components with an executable specification language facilitates the specification prototyping of embedded distributed systems. The specification language should cover process management, timing, and communication commands that real-time executive and communication task services of every node prototype can interpret. We use a technique that employs attribute grammars and either a macro processor or Prolog to execute the language     

Model driven middleware: A new paradigm for developing distributed real-time and embedded systems

Distributed real-time and embedded (DRE) systems have become critical in domains such as avionics (e.g., flight mission computers), telecommunications (e.g., wireless phone services), tele-medicine (e.g., robotic surgery), and defense applications (e.g., total ship computing environments). These types of system are increasingly interconnected via wireless and wireline networks to form systems of systems. A challenging requirement for these DRE systems involves supporting a diverse set of quality of service (QoS) properties, such as predictable latency/jitter, throughput guarantees, scalability, 24x7 availability, dependability, and security that must be satisfied simultaneously in real-time. Although increasing portions of DRE systems are based on QoS-enabled commercial-off-the-shelf (COTS) hardware and software components, the complexity of managing long lifecycles (often ∼15-30 years) remains a key challenge for DRE developers and system integrators. For example, substantial time and effort is spent retrofitting DRE applications when the underlying COTS technology infrastructure changes.This paper provides two contributions that help improve the development, validation, and integration of DRE systems throughout their lifecycles. First, we illustrate the challenges in creating and deploying QoS-enabled component middleware-based DRE applications and describe our approach to resolving these challenges based on a new software paradigm called Model Driven Middleware (MDM), which combines model-based software development techniques with QoS-enabled component middleware to address key challenges faced by developers of DRE systems — particularly composition, integration, and assured QoS for end-to-end operations. Second, we describe the structure and functionality of CoSMIC (Component Synthesis using Model Integrated Computing), which is an MDM toolsuite that addresses key DRE application and middleware lifecycle challenges, including partitioning the components to use distributed resources effectively, validating software configurations, assuring multiple simultaneous QoS properties in real-time, and safeguarding against rapidly changing technology.     

Language constructs for real-time distributed systems

The paper observes syntactic and semantic requirements for a language for programming real-time distributed systems. A proposal for language features that meet these requirements is offered, and the features are applied to an example.     

Synchronized UTC for distributed real-time systems

We present a novel technique for establishing a highly accurate global time in fault-tolerant, large-scale distributed real-time systems. Unlike the usual clock synchronization approaches, our clock validation technique provides a precise system time that also relates to an external time standard like UTC with high accuracy. The underlying idea is to validate time information of external time sources like GPS-receivers against a global time maintained by the local clocks in the system. As an example, a promising interval-based clock validation algorithm ICV that exhibits excellent fault-tolerance properties is outlined and analyzed. It requires only a few high-accurate external time sources and provides each node with the actual accuracy of its clock.     

Virtual machines for distributed real-time systems

The steady increase in raw computing power of the processors commonly adopted for distributed real-time systems leads to the opportunity of hosting diverse classes of tasks on the same hardware, for example process control tasks, network protocol stacks and man–machine interfaces.This paper describes how virtualization techniques can be used to concurrently run multiple operating systems on the same physical machine, although they are kept fully separated from the security and execution timing points of view, and still have them exhibit acceptable real-time execution characteristics.With respect to competing approaches, the main advantages of this method are that it requires little or no modifications to the operating systems it hosts, along with a better modularity and clarity of design.     

Monitoring distributed real-time systems

This paper emphasizes the power ofmonitoring of distributed real-time systems as a promising tool for both scientific work and practical purposes. Starting out from a number of well-known problems with today's (industrial) real-time systems, a classification of remedial monitoring applications is given. The most important features of a monitoring system suitable for such purposes are discussed and related to the current research into monitoring of (general) distributed systems. Finally, some of the resulting conceptual issues underlying our prototype VTA monitoring system—currently being under development at our department—are presented.