Michael González Harbour

A practitioner's handbook for real-time analysis

Preface. Part 1: Introduction. 1. About this Handbook. 2. Fundamentals of RMA. Part 2: Concepts and Techniques. 3. A Framework for Describing Real-Time Systems. 4. Techniques for Analyzing Timing Behavior. Part 3: Analyzing Real-Time Systems. 5. Basic Real-Time Situations. 6. Advanced Real-Time Situations. 7. Effects of Operating System and Runtime Services on Timing Analysis. Part 4: Using the Handbook on Realistic Systems. 8. Analyzing Complex Systems. 9. Designing with Rate Monotonic Analysis. Part 5: Appendices. A. Rules of Thumb. B. Notation Used in this Handbook. C. Bibliography. D. Glossary. E. Index.

Timing analysis for fixed-priority scheduling of hard real-time systems

This paper presents a timing analysis for a quite general hard real-time periodic task set on a uniprocessor using fixed-priority methods. Periodic tasks are composed of 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 and subtask is presented along with its theoretical underpinnings. This method can be used to analyze the schedulability of any task set on a uniprocessor whose priority structure can be modeled as serially executed subtasks, which can lead to a very complex priority structure. Important examples include task sets that involve interrupts, certain synchronization protocols, certain precedence constraints, nonpreemptible sections, and some message-passing systems. The method is illustrated by a robotics example. >

Fixed priority scheduling periodic tasks with varying execution priority

The problem of fixed priority scheduling of periodic tasks where each tasks execution priority may vary is considered. Periodic tasks are decomposed into serially executed subtasks, where each subtask is characterized by an execution time and a fixed priority and is permitted to have 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 and, in general, any mechanism that contributes to a complex priority structure. The authors introduce a simple but realistic real-time robotics application and illustrate how one uses the schedulability equations presented.<<ETX>>

Exploiting precedence relations in the schedulability analysis of distributed real-time systems

In this paper we present improved techniques for the schedulability analysis of tasks with precedence relations in multiprocessor and distributed systems scheduled under a pre-emptive fixed priority scheduler. Recently developed techniques, based on the analysis of tasks with dynamic offsets, take into account the precedence relations between tasks only indirectly, through terms iteratively estimated from the response times of the tasks. With the techniques presented in this paper, we exploit the precedence relations in a more accurate way, and we also take advantage of the priority structure of the different tasks. These considerations permit a significant improvement of the results of the analysis applied to distributed and multiprocessor systems.

Influence of different system abstractions on the performance analysis of distributed real-time systems

System level performance analysis plays a fundamental role in the design process of real-time embedded systems. Several different approaches have been presented so far to address the problem of accurate performance analysis of distributed embedded systems in early design stages. The existing formal analysis methods are based on essentially different concepts of abstraction. However, the influence of these different models on the accuracy of the system analysis is widely unknown, as a direct comparison of performance analysis methods has not been considered so far. We define a set of benchmarks aimed at the evaluation of performance analysis techniques for distributed systems. We apply different analysis methods to the benchmarks and compare the results obtained in terms of accuracy and analysis times, highlighting the specific effects of the various abstractions. We also point out several pitfalls for the analysis accuracy of single approaches and investigate the reasons for pessimistic performance predictions.

Schedulability analysis of distributed hard real-time systems with multiple-event synchronization

Presents a schedulability analysis technique for distributed hard real-time systems in which responses to different events may synchronize with each other. This technique uses a representation model for distributed systems that allows us to describe not only the task synchronization due to resource sharing, but also the activation due to combinations of events or the generation of several events by a single task. The model is representative of a large number of systems and is suitable for the treatment of message-passing systems or the client-server architecture. The analysis technique is based on the existing rate monotonic analysis (RMA) techniques for analyzing distributed real-time systems; it allows obtaining upper bounds for the worst-case response times of the system, thus allowing us to make guarantees about the fulfillment of the timing requirements that have been imposed.

Minimizing the effects of jitter in distributed hard real-time systems

Abstract In this paper we present a study of the effects caused on distributed real-time systems by the presence of jitter in the activation of tasks and messages. We show that although jitter has usually a small impact on the schedulability of single-processor systems, in distributed architectures the worst-case response times are significantly delayed. Reducing or eliminating jitter in these systems can increase the schedulability of the system up to 50% more than when jitter is permitted. The delay effects caused by jitter can be prevented by using a bandwidth-preserving scheduling algorithm such as the sporadic server. Since this kind of scheduling policy is not designed for communication networks, we describe in this paper how to adapt and implement the sporadic server algorithm on communication networks. Using the sporadic server both in the processors and networks, we can build distributed systems with up to 100% utilization of the CPUs and communication resources, while still guaranteeing that hard real-time requirements are met.

Schedulability Analysis and Optimization of Heterogeneous EDF and FP Distributed Real-Time Systems

The increasing acceptance of the Earliest Deadline First (EDF) scheduling algorithm in industrial environments, together with the continued usage of Fixed Priority (FP) scheduling is leading to heterogeneous systems with different scheduling policies in the same distributed system. Schedulability analysis techniques usually consider the entire system as a whole (holistic approach), with only one preestablished scheduling policy in all the resources. In this work, composition mechanisms will be presented that enable us to combine different FP and EDF response-time analysis techniques for checking the schedulability of heterogeneous systems. Additionally, priority and scheduling deadline assignment techniques will be combined into a new algorithm called HOSPA (Heuristic Optimized Scheduling Parameters Assignment), for optimizing the assignment of priorities and scheduling deadlines to tasks and messages in heterogeneous distributed hard real-time systems.

Modeling distributed real-time systems with MAST 2

Abstract Switched networks have an increasingly important role in real-time communications. The IEEE Ethernet standards have defined prioritized traffic (802.1p) and other QoS mechanisms (802.1q). The Avionics Full-Duplex Switched Ethernet (AFDX) standard defines a hard real-time network based on switched Ethernet. Clock synchronization is also an important service in some real-time distributed systems because it allows a global notion of time for event timing and timing requirements. In the process of defining the new MAST 2 model, clock synchronization modeling capabilities have been added, and the network elements have been enhanced to include switches and routers. This paper introduces the schedulability model that will enable an automatic schedulability analysis of a distributed application using switched networks and clock synchronization mechanisms.

Reliable Software Technologies — Ada-Europe’ 99

While there are appear to be many ways in which real-time Ada systems can be designed, it is observed that they can be described using four architectural families: the Timeline, Event-Driven, Pipeline, and Client-Server architectures. This paper describes the principal characteristics of each of these architecture families with respect to their ability to provide bounded application response times, their cost, and safety at a high level. In addition, the use of important Ada constructs for each architecture family is discussed, and examples of application domains that use each of these architectures are identified.