Real-Time Software Architecture: Application to FIP Fieldbus

2002

Abstract This paper presents a method to analyze the timing behavior of an event-based real-time protocol composition framework. The framework, called RT-Appia, allows the development and implementation of configurable real-time protocol stacks. The method performs the schedulability analysis for events flowing in a real-time channel and is based on the holistic theory for distributed real-time systems.

… , IEEE Transactions on, 2002

The WorldFIP protocol is one of the profiles that constitute the European fieldbus standard EN-50170. It is particularly well suited to be used in distributed computer-controlled systems where a set of process variables must be shared among network devices. To cope with the real-time requirements of such systems, the protocol provides communication services based on the exchange of periodic and aperiodic identified variables. The periodic exchanges have the highest priority and are executed at run time according to a cyclic schedule. Therefore, the respective schedulability can be determined at pre-run-time when building the schedule table. Concerning the aperiodic exchanges, the situation is different since their priority is lower and they are handled according to a first-come-first-served policy. In this paper, a response-time-based schedulability analysis for the real-time traffic is presented. Such analysis considers both types of traffic in an integrated way, according to their priorities. Furthermore, a fixed-priorities-based policy is also used to schedule the periodic traffic. The proposed analysis represents an improvement relative to previous work and it can be evaluated online as part of a traffic online admission control. This feature is of particular importance when a planning scheduler is used, instead of the typical offline static scheduler, to allow online changes to the set of periodic process variables. since 2000.

Real-time constraints play an important role in the speci cation of communication protocols. We present three practical real-time speci cation methods, SDL, real-time extended LOTOS and Message Sequence Charts in combination with real-time temporal logic, and exemplify their application to the speci cation of real-time aspects in communication protocols. We discuss their suitability for di erent types of real-time constraints and observe that di erent speci cation styles are suitable for di erent application areas.

Wiley Encyclopedia of Computer Science and Engineering, 2009

2006

Scheduling theory generally assumes that real-time systems are mostly composed of activities with hard real-time requirements. Many systems are built today by composing different applications or components in the same system, leading to a mixture of many different kinds of requirements with small parts of the system having hard real-time requirements and other larger parts with requirements for more flexible scheduling and for quality of service. Hard real-time scheduling techniques are extremely pessimistic for the latter part of the application, and consequently it is necessary to use techniques that let the system resources be fully utilized to achieve the highest possible quality. This paper presents a framework for a scheduling architecture that provides the ability to compose several applications or components into the system, and to flexibly schedule the available resources while guaranteeing hard real-time requirements. The framework (called FSF) is independent of the underlying implementation, and can run on different underlying scheduling strategies. It is based on establishing service contracts that represent the complex and flexible requirements of the applications, and which are managed by the underlying system to provide the required level of service.

2000

Over the last few years, there has been considerable research in the area of Software Architecture. However, relatively little attention has been paid to the specification of real-time properties of such architectures. This paper presents the Xelha architectural description language which is intended to overcome this deficiency. The language offers both a task model and a resource model. The former models component interactions as tasks with associated pools of resources. The latter provides hierarchies of abstract resources. In addition, the use of object-oriented typing allow us to introduce some dynamism to architecture specifications. Finally, Xelha provides support for the specification of both static QoS management (i.e. desired level of QoS) and dynamic QoS mangement (i.e. mechanisms to attain the contracted level of QoS).

Proceedings of 5th International Workshop on Parallel and Distributed Real-Time Systems and 3rd Workshop on Object-Oriented Real-Time Systems, 1997

The demand for more and more complex real-time applications which require high computational needs with timing constraints, and geographical distribution of computational entities (tasks) of these applications, have led to the choice of distributed systems as a natural candidate for supporting such real-time applications, due to their potential for high performance and reliability. The distributed real-time system considered here consists of uniprocessor or multiprocessor nodes connected through a multihop network. Scheduling of tasks in such a system involves schedulingof dynamically arriving tasks within a node (local scheduling), migration of tasks across the network (global scheduling) if it is not possible to schedule them locally, and (iii) scheduling of messages on communication links (message scheduling) to support inter-task communication and task migration. Most of the existing schemes on scheduling in distributed real-time systems have addressed each of these issues in isolation. Moreover, these schemes consider the load on the processors at a node as the basis to migrate tasks from a heavily loaded node (sender) to a lightly loaded node (receiver). We believe that the identi cationof a receiver node should be based not only on the load on its processors, but also on the availability of a path, which satis es the bandwidth required for the task migration, from the sender to that receiver. In this paper, we present an integrated framework for scheduling dynamically arriving real-time tasks in distributed real-time systems. Our proposal consists of (i) algorithms for global scheduling and (ii) interactions among the three schedulers in a way to improve the schedulability of the system. The e ectiveness of the proposed framework has been evaluated through simulation by comparing it with existing schemes.

2003

Real-time distributed systems are becoming pervasive, supporting a broad range of applications such as avionics, automotive, adaptive control, robotics, computer vision and multimedia. In such systems, several activities are executed on different nodes and cooperate via message passing. One increasingly important concept is that of Quality-of-Service (QoS), i.e. a system performance metric from the application point-of-view. Concerning the communication system, the QoS delivered to the application is a function of communication parameters such as the rates of message streams. In previous work, the authors have developed two network protocols, FTT-CAN and FTT-Ethernet, which allow on-line changes to the set of message streams under guaranteed timeliness. In this paper, the specific network protocols are abstracted away leading to a generic communication paradigm named Flexible Time-Triggered (FTT), which supports on-line QoS management, with arbitrary policies, in distributed realtime systems. Two possible QoS management policies are referred, priority-based and another one based on the elastic task model, and their use is illustrated with a case study.

Control Engineering Practice, 1998

Extensively discussed for decades, it is only relatively recently that a demand for true real-time industrial communication systems has become evident. However, when the requirements of such systems are understood, few of the offered solutions are appropriate. This paper suggests that. in order to produce such systems, rigorous specification, design and verification processes are necessary, and that these must all be capable of handling logical and temporal analysis and design. To achieve this, it is suggested that a mixture of tools is (currently) necessary, and that these tools should include object-oriented design techniques with temporal extensions. The points are illustrated by reference to the recent development of a real-time fieldbus system, built around the CAN protocol, which supports true real-time communication over an existing, commercial system.