实时多任务过程控制机软件设计

本文从实用角度论述了一种可用于分布式系统和用户控制任务相对独立环境的实时多任务过程控制软件的整体设计思想、软件结构和实现的一般方法。文中还分别给出了两级系统监控级和过程控制级软件的实例。     

Implementation of Hard Real-Time Embedded Control Systems

Although the domain of hard real-time systems has been thoroughly elaborated in the academic sphere, embedded computer control systems –- being an important component in mechatronic designs –- are seldom dealt with consistently. Often, off-the-shelf computer systems are used, with no guarantee that they will be able to meet the requirements specified. In this paper, a design for embedded control systems is presented. Particularly, the paper deals with the hardware architecture and design details, the operating system, and high-level real-time language support. It is shown how estimates of process run-times necessary for schedulability analysis can be acquired on the basis of deterministic behavior of the hardware platform.     

Replication Management in Reliable Real-Time Systems

Building reliable real-time applications on top of commercial off-the-shelf (COTS) components is not a straightforward task. Thus, it is essential to provide a simple and transparent programming model, in order to abstract programmers from the low-level implementation details of distribution and replication. However, the recent trend for incorporating pre-emptive multitasking applications in reliable real-time systems inherently increases its complexity. It is therefore important to provide a transparent programming model, enabling pre-emptive multitasking applications to be implemented without resorting to simultaneously dealing with both system requirements and distribution and replication issues. The distributed embedded architecture using COTS components (DEAR-COTS) architecture has been previously proposed as an architecture to support real-time and reliable distributed computer-controlled systems (DCCS) using COTS components. Within the DEAR-COTS architecture, the hard real-time subsystem provides a framework for the development of reliable real-time applications, which are the core of DCCS applications. This paper presents the proposed framework, and demonstrates how it can be used to support the transparent replication of software components.     

Explicit sub-optimal linear quadratic regulation with state and input constraints

Optimal feedback solutions to the infinite horizon LQR problem with state and input constraints based on receding horizon real-time quadratic programming are well known. In this paper we develop an explicit solution to the same problem, eliminating the need for real-time optimization. It is shown that the resulting feedback controller is piecewise linear. This explicit functional structure is exploited for efficient real-time implementation. A suboptimal strategy, based on a suboptimal choice of a finite horizon and imposing additional limitations on the allowed switching between active constraint sets on the horizon, is suggested in order to address the computer memory and processing capacity requirements of the explicit solution.     

A Gauss–Seidel type solver for the fast computation of input-constrained control systems

An important class of nonlinear control systems can be represented as the feedback interconnection of two parts: a linear time-invariant system and a block of decentralized nonlinearities. When the linear time-invariant part has a nontrivial feedthrough term or the nonlinearity has a feedback gain, control computation involves the online implementation of a multivariable algebraic loop which must be resolved at each sampling instant. The requirements for such online computation may result in several implementation issues, especially in real-time and embedded control applications. This paper considers the implementation of such algebraic loops arising from several input-constrained systems. The proposed solution algorithm is globally convergent for a very large class of feedthrough or feedback gains and shows promise for real-time and embedded control applications where a fast but approximate solution is of the essence.     

ARMADA Middleware and Communication Services

Real-time embedded systems have evolved during the past several decades from small custom-designed digital hardware to large distributed processing systems. As these systems become more complex, their interoperability, evolvability and cost-effectiveness requirements motivate the use of commercial-off-the-shelf components. This raises the challenge of constructing dependable and predictable real-time services for application developers on top of the inexpensive hardware and software components which has minimal support for timeliness and dependability guarantees. We are addressing this challenge in the ARMADA project.ARMADA is set of communication and middleware services that provide support for fault-tolerance and end-to-end guarantees for embedded real-time distributed applications. Since real-time performance of such applications depends heavily on the communication subsystem, the first thrust of the project is to develop a predictable communication service and architecture to ensure QoS-sensitive message delivery. Fault-tolerance is of paramount importance to embedded safety-critical systems. In its second thrust, ARMADA aims to offload the complexity of developing fault-tolerant applications from the application programmer by focusing on a collection of modular, composable middleware for fault-tolerant group communication and replication under timing constraints. Finally, we develop tools for testing and validating the behavior of our services. We give an overview of the ARMADA project, describing the architecture and presenting its implementation status.     

Enabling fuzzy technologies in high performance networking via an open FPGA-based development platform

Soft computing techniques and particularly fuzzy inference systems are gaining momentum as tools for network traffic modeling, analysis and control. Efficient hardware implementations of these techniques that can achieve real-time operation in high-speed networking equipment as well as other highly time-constrained application fields is however an open problem. We introduce a development platform for fuzzy inference systems with applications to network traffic analysis and control. The platform addresses the current requirements and constraints of high performance networking equipment. For the development process, we set up a methodology and a CAD tool chain that span the entire design process from initial specification in a high-level language to implementation on FPGA devices. An FPGA development board with PCI/PCIe interface is employed to support an open platform that comprises CAD tools as well as IP cores. PCI compatible fuzzy inference modules are implemented as System-on-Programmable-Chip (SoPC). We present satisfactory experimental results from the implementation of fuzzy systems for a number of applications in analysis and control of Internet traffic. These systems are shown to satisfy operational and architectural requirements of current and future high performance routing equipment. The platform proposed allows for the development of prototypes while avoiding large investments and complicated management procedures which constrain the testing and adoption of soft computing techniques in high performance networking.     

一种基于乐观方法的安全实时并发控制协议

实时数据库通常应用在一些安全关键类应用中，如电子商务、股票交易、军事指挥系统等。在这样一些应用中，实时数据库系统需同时满足两方面的需求：确保数据安全和尽可能减低实时事务错过截止期的比率。然而，通常这两方面需求是相互冲突的，满足一方面是以牺牲另一方面为代价。本文提出了一种基于乐观方法的安全实时并发控制协议，该协议将安全约束整合到实时乐观并发控制协议中，并能根据应用的需求在安全性和实时性方面进行了适当的折中。性能测试结果显示，该协议在确保数据安全的同时并未明显地降低实时性能。     

Concept of a crossbar switch for large-scale multiple processor systems in the field of process control

Large-scale multiple processor systems are already widely used in the field of process control. They are real-time systems and differ considerably from traditional computer systems. Such systems are used to perform a large variety of relatively complex tasks, many of them extremely time-critical. In the near future, the tasks will increase in number and size and will become even more time-critical, caused, for instance, by the expected integration of expert systems in process control. The question naturally arises as to whether or not such an increase of the requirements could be met by a straightforward enhancement of present designs [10], the interconnection network being in any case the key issue.

The paper describes the concept of a new crossbar switch design, based on the use of so-called configurational processors that would be extraordinarily well suited to the specific requirements in the field of process control. The new design principle is VLSI-compatible; the whole crossbar switch can be implemented with building blocks of one type. It is possible to arrange these components for the crossbar switch in close proximity to the processing elements, which are physically distributed throughout the whole area of a plant. This characteristic, in combination with the use of bitserial buses, allows a crossbar switch to be implemented in an advantageous manner, particularly without excessive cabling costs.     

Problems with expert systems in real-time control

There is increasing use of knowledge-based or expert systems in the process and manufacturing industries, with currently in excess of 2000 installations. The advantage offered by such systems is their ability to deal with complex and possibly incorrect or incomplete data. A new generation of expert-system tools, designed specifically for real-time control applications, has been developed. This paper examines the requirements of an expert system for real-time control, and shows how current approaches attempt to meet them. It is argued that none of the currently available tools fully satisfy the needs of a real-time expert control system, particularly in terms of reliability and guaranteed real-time response.