An object-oriented real-time programming language

2006

IEEE Transactions on Software Engineering, 1994

This paper considers the problem of timing analysis for a quite general hard real-time periodic task set on a uniprocessor using fixed priority methods. Periodic tasks are decomposed into serially executed subtasks, where each subtask is characterized by an execution time, a fixed priority, and a deadline. A method for determining the schedulability of each task is presented along with its theoretical underpinnings. This method can be used to analyze the schedulability of complex task sets which involve interrupts, certain synchronization protocols, nonpreemptible sections, certain precedence constraints, and, in general, any mechanism that contributes to a complex priority structure. The method is illustrated with a realistic example.

In this paper we study hard real-time systems composed of periodic preemptive tasks and address the scheduling problem on specific hardware platforms. For such a system, the failure to satisfy any constraint may have disastrous consequences. An important starting point for the analysis of such systems is the basic task model considered. In this paper we introduce a new model, relative to the ones in the literature, that is able to obtain stronger schedulability conditions. This new model provides a formal and rigorous specification of a task and helps us to describe the schedulability principle when tasks are scheduled by using a fixed-priority scheduling policy.

[1992] Proceedings Real-Time Systems Symposium, 1992

Real-time operating systems generally depend on some form of priority information for making scheduling decisions. Priorities may take the form of small integers or deadline times, for example, and the priorities indicate the preferred order for execution of the jobs. Unfortunately, most systems suffer from some degree of priority inversion where a high priority job must wait for a lower priority job to execute. We consider the nature of the non-preemptible code sections, called critical sections or critical regions, which give rise to this priority inversion in the context of a soft real-time operating system where average response time for different priority classes is the primary performance metric. An analytical model is described which is used to illustrate how critical regions may affect the timeconstrained jobs in a multimedia (soft real-time) task set.

Proceedings of the IEEE, 1994

Real-time computing systems are used to control telecommunication systems, defense systems, avionics, and modern factories. Generalized rate-monotonic scheduling theory is a recent development that has had large impact on the development of real-time systems and open standards. In this paper we provide an upto-date and selfcontained review of generalized rate-monotonic scheduling theory. We show how this theory can be applied in practical system development, where special attention must be given to facilitate concurrent development by geographically distributed programming teams and the reuse of existing hardware and software components. I. INTRODUCTION Real-time computing systems are critical to an industrialized nation's technological infrastructure. Modern telecommunication systems, factories, defense systems, aircraft and airports, space stations, and high-energy physics experiments cannot operate without them. Indeed, real-time computing systems control the very systems that keep us productive, and enable us to explore new frontiers of science and engineering. In real-time applications, the correctness of a computation depends upon not only its results but also the time at which outputs are generated. The measures of merit in a real-time system include: Predictably fast response to urgent events. High degree of schedulability. Schedulability is the degree of resource utilization at or below which the timing requirements of tasks can be ensured. It can be thought as a measure of the number of timely transactions per second.

2009

In order to take semantical aspects into account for the scheduling problem and obtain scheduling results for a wide class of systems, we extend the Petri net scheduling approach for real-time systems. Our study focuses on tasks with conditional statements. Classical approaches consider only the worst case execution time that occurs in the different branches of conditional statements and don't take the semantic of the tasks into account. We show that this pessimistic model can lead to wrong conclusions for scheduling. We extend the task model with conditional statements, and the notion of schedule is replaced by the notion of scheduling tree. We propose then a model approach using Petri nets in order to explicitly take conditional instructions and their semantics into account.

Computer Physics Communications, 1986

Real-time programming is a discipline of great importance not only in process control, but also in fields like communication, office automation, interactive databases, interactive graphics and operating systems development.

Formal Aspects of Computing, 1995

Assume that a real-time programP T consisting of a number of parallel processes is executed on a system having a setPr of processors which are shared between the processes by a real-time schedulerS T. Assume that PT must meet some timing deadlines. We show that such an implementation ofP T can be represented as a transformationL(P T) and that the deadlines ofP T will be met if they are satisfied by the timing properties of the transformed program. The condition for feasibility of a real-time program executed under a scheduler is formalized and rules are provided for verification. The schedulerS T can be specifiedgenerically and applied to different programs, making it unnecessary to introduce low-level operations such as scheduling primitives into the programming language. Thus real-time program specification and Schedulability can be considered in the same framework and the timing properties of a program can be determined at the specification level. By separating the specification of the scheduler from that of the program, the feasibility of an implementation can be proved by considering a scheduling policy rather than its implementation details.

Software: Practice and Experience, 1995

More and more programmers find their software being used in performance critical applications. Unfortunately, they have limited techniques at their disposal to help guarantee this particular aspect of their programs. There has been considerable activity in recent years on developing analysis techniques for hard real-time systems. Inevitably these techniques make simplifying assumptions so as to reduce the complexity of the problem to be solved. For example hard realtime schedulability analysis techniques often assume that the timing properties of the underlying kernel can be accounted for by incorporating extra execution time into the application tasks. Furthermore, they assume that the application task structure is very simple and uniform. This paper considers the implications of using these techniques in the analysis of a typical single processor application, the attitude and orbital control system (AOCS) for the Olympus satellite. The paper outlines a common approach for estimating the response times for tasks, and then extends the scheduling equations so that they can be used in the engineering of realistic realtime systems.

Theoretical Computer Science, 2001

A real-time program can be developed by reÿning a speciÿcation into program code. Veriÿcation of the timing properties of the program is then usually done at two levels: veriÿcation of the ordering of timed actions in the program and proof that execution of the program on a speciÿc system will meet its timing requirements. Reÿnement is done within a formal model but the second step requires a di erent framework in which scheduling theory analysis is used and actual program execution times can be taken into account. The implementation of a program on a system is said to be feasible or schedulable if it will meet all the timing deadlines.