Giotto provides an abstract programmer's model for the implementation of embedded control systems with hard real-time constraints. A typical control application consists of periodic software tasks together with a mode switching logic for enabling and disabling tasks. Giotto speci es timetriggered sensor readings, task invocations, and mode switches independent of any implementation platform. Giotto can be annotated with platform constraints such as task-to-host mappings, and task and communication schedules. The annotations are directives for the Giotto compiler, but they do not alter the functionality andtiming of a Giotto program. By separating the platform-independent from the platform-dependent concerns, Giotto enables a great deal of exibility inchoosing control platforms as well as a great deal of automation in the validation and synthesis of control software. The timetriggered nature of Giotto achieves timing predictability, which makes Giotto particularly suitable for safety-critical applications.

: Controller Area Network (CAN) is a well designed communications bus for sending and receiving short real-time control messages at speeds of up to 1Mbit/sec. One of the perceived drawbacks to CAN has been the inability to bound accurately the worst-case response time of a given message (i.e. the longest time between queueing the message and the message arriving at the destination processors). This paper presents analysis to bound such response times, including the costs of error handling and re-transmission. Key Words: real-time systems; real-time communications; scheduling theory; scheduling analysis; distributed systems 1. INTRODUCTION The Controller Area Network (CAN) [3] is a well designed communications bus for sending and receiving short real-time control messages. The bus is designed to connect control systems over a small area (such as automobiles), operating in a noisy environment at speeds of up to 1Mbit/sec. One of the perceived problems of CAN is the inability to bo...

The increasing use of communication networks in time critical applications presents engineers with fundamental problems with the determination of response times of communicating distributed processes. Although there has been some work on the analysis of communication protocols, most of this is for idealised networks. Experience with single processor scheduling analysis has shown that models which abstract away from implementation details are at best very pessimistic and at worst lead to unschedulable system being deemed schedulable. In this paper, we derive idealised scheduling analysis for the CAN network, and then study two actual interface chips to see how the analysis can be applied. 1. Introduction One of the fundamental difficulties in engineering hard real-time systems is the development of analysis to bound the timing behaviour of the system. Much work in recent years has been developing this analysis for a run-time dispatching algorithm known as fixed priority preemptive sch...

Analysis is presented that enables the worst case latencies for Controller Area Network (CAN) messages to be predicted. The analysis is illustrated in terms of the Intel 82527 controller and applied to a SAE benchmark. This benchmark contains some 53 message types; all of which are analysed for various transmission rates. Techniques are presented that enables the temporal behaviour of a CAN system to be improved. In particular the impact of message "piggybacking" is assessed. The paper concludes by considering error recovery, and presents a framework into which different failure models can be incorporated and analysed (in terms of the impact failures have on message latencies).

This paper discusses the addition of so-called time offsets to task sets dispatched according to fixed priorities. The motivation for this work is two-fold: firstly, direct expression of time offsets is a useful structuring approach for designing complex hard real-time systems. Secondly, analysis directly addressing time offsets can be very much less pessimistic than extant analysis. In this report we extend our current fixed priority schedulability analysis, and then present two major worked examples, illustrating the approach. 1. INTRODUCTION Previous work has addressed the problem of determining the worst-case timing behaviour of tasks dispatched according to fixed priority scheduling [11, 10]. Much of this work has been aimed at determining the worst-case case response time of a given task; of course, the worst-case response time is, by definition, the response time of the task in the worst-case scheduling scenario. So far, in all these previous pieces of work, tasks have been ass...

Automatic control applications are real-time systems which pose stringent requirements on precisely time-triggered synchronized actions and constant end-to-end delays in feedback loops which involve multirate interactions. Motivated by the apparent gap between computer science and automatic control theory, a set of requirements for real-time implementation of control applications is given. A real-time behavioral model for control applications is then presented and exemplified. Important sources and characteristics of time-variations in distributed computer systems are investigated. This illuminates key execution strategies to ensure the required timing behaviour. Implications on design and implementation and directions for further work are discussed.

This paper describes the structure of the STRESS language and its environment, and gives examples of its use

In a distributed hard real-time system, communications between tasks on different processors must occur in bounded time. The inevitable communication delay is composed of both the delay in transmitting a message on the communications media, and also the delay in delivering the data to the destination task. This paper derives schedulability analysis bounding the media access delay and the delivery delay. Two access protocols are considered: a simple timed token passing approach, and a real-time priority broadcast bus. A simple delivery approach is considered where the arrival of a message generates an interrupt --- the so-called `on demand' approach. 1. INTRODUCTION A hard real-time system is often composed from a number of periodic and sporadic tasks which communicate their results by passing messages; in a distributed system these messages are sent between processors across a communications device. In order to guarantee that the timing requirements of all tasks are met, the communica...

In many distributed real-time systems, the workload can be modeled as a set of periodic tasks, each of which consists of a chain of subtasks executing on different processors. Synchronization protocols are used to govern the release of subtasks so that the precedence constraints among subtasks are satisfied and the schedulability of the resultant system is analyzable. When different protocols are used , tasks can have different worst-case and average end-to-end response times. This paper focuses on distributed real-time systems that contain independent, periodic tasks scheduled by fixed-priority scheduling algorithms. It describes three synchronization protocols together with algorithms to analyze the schedulability of the system when these protocols are used. Simulation was conducted to compare the performance of these protocols with respect to the worst-case and average case end-to-end response times. The simulation experiment and the performance of the protocols are described. 1 Int...

: A uniform, flexible approach is proposed for analysing the feasibility of deadline scheduled real-time systems. In its most general formulation, the analysis assumes sporadically periodic tasks with arbitrary deadlines, release jitter, and shared resources. System overheads of a tick driven scheduler implementation, and scheduling of soft aperiodic tasks are also accounted for. A procedure for the computation of task worst-case response times is also described for the same model. While this problem has been largely studied in the context of fixed priority systems, we are not aware of other works that have proposed a solution to it when deadline scheduling is assumed. The worst-case response time evaluation is a fundamental tool for analysing end-to-end timing constraints in distributed systems [21]. Key-words: real-time, scheduling, feasibility analysis, response times. (R'esum'e : tsvp) This work has been supported by the Commission of the European Communities under contract ERBC...