The ART (Advanced Real-Time Technology) Project is engaged in wide ranging research on hard real-time systems. The project has as its overall goal the development and demonstration of predictable and fault tolerant hard real- time computer systems. To achieve this goal, research is being conducted in three interrelated areas: The development of a theory of hard real-time resource management including scheduling and synchronization. In addition, this theory is being applied in a wide range of contexts including databases, communication networks, operating systems and artificial intelligence. The design and construction of an operating system (ARTS) that supports predictable and fault tolerant real-time computer systems and demonstration and testing in the ARTS testbed to provide proof of concept and to gain understanding into aspects of the theory needing further refinement. A real-time version of the Mach operating system, RT-Mach, is also being developed as a part of the project. Development of hardware architectures and approaches to fault tolerance that can support predictable hard real-time computer systems.

With spacecraft designs placing more emphasis on reduced cost, faster design time, and higher performance, it is easy to understand why more commercial-off-the-shelf (COTS) devices are being used in space based applications. The COTS devices offer spacecraft designers shorter design-to- orbit times, lower system costs, orders of magnitude better performance, and a much better software availability than their radiation hardened (radhard) counterparts. The major drawback to using COTS devices in space is their increased susceptibility to the effects of radiation, single event upsets (SEUs) in particular. This thesis will focus on the implementation of a fault tolerant computer system. The hardware design presented here has two different benefits. First, the system can act as a software testbed, which allows testing of software fault tolerant techniques in the presence of radiation induced SEUs. This allows the testing of the software algorithms in the environment they were designed to operate in without the expense of being placed in orbit. Additionally, the design can be used as a hybrid fault tolerant computer system. By combining the masking ability of the hardware with supporting software, the system can mask out and reset processor errors in real time. The design layout will be presented using OrCAD schematics.

Real-time computer systems are very often subject to dependability requirements because of their application areas. Fly-by-wire airplane control systems, control of power plants, industrial process control systems and others are required to continue their function despite faults. Fault-tolerance and real-time requirements thus constitute a kind of natural combination in process control applications. Systematic fault-tolerance is based on redundancy, which is used to mask failures of individual components. The problem of replica determinism is thereby to ensure that replicated components show consistent behavior in the absence of faults. It might seem trivial that, given an identical sequence of inputs, replicated computer systems will produce consistent outputs. Unfortunately, this is not the case. The problem of replica non-determinism and the presentation of its possible solutions is the subject of Fault-Tolerant Real-Time Systems: The Problem of Replica Determinism. The field of automotive electronics is an important application area of fault-tolerant real-time systems. Systems like anti-lock braking, engine control, active suspension or vehicle dynamics control have demanding real-time and fault-tolerance requirements. These requirements have to be met even in the presence of very limited resources since cost is extremely important. Because of its interesting properties Fault-Tolerant Real-Time Systems gives an introduction to the application area of automotive electronics. The requirements of automotive electronics are a topic of discussion in the remainder of this work and are used as a benchmark to evaluate solutions to the problem of replica determinism.

The goals of this project were the development of performance measures suitable for use in real-time embedded systems. Developed a network measure to guide the designer in choosing an appropriate network topology. The measure combines graphic-theoretic concepts in evaluating the underlying reliability of the network and other means to evaluate the ability of the network to support interprocessor traffic. A second measure, called the computer measure, is meant to evaluated the computer system in terms that are of importance for real-time applications. A simulator testbed called TRIDENT was built to evaluate the network and surge measures. Much of the technology developed under this project is being transferred to the Jet Propulsion Laboratory (JPL).

BY H. KOPETZ A real-time computer system must provide the intended service in two di mensions: the functional (value) dimension and the temporal dimension. The verification of a real-time system implementation is thus necessarily more com plex than the verification of a non-real-time system which has to be checked in the value dimension only. Since the formal verification techniques of temporal properties have not yet matured to the point where these techniques can be used in practical system development, systematic design and testing are the only alternatives for the development of dependable real-time systems. At present, up to and more than fifty percent of the development eff'ort of complex real-time computer systems is spent on testing. The test activities are thus a significant cost element in any real-time system project. The attack on this cost element has to proceed from two fronts: the design for testability and the development of a systematic test methodology supported by an appropriate tool set. This book covers both of these topics.

The design of computer systems to be embedded in critical real-time applications is a complex task. Such systems must not only guarantee to meet hard real-time deadlines imposed by their physical environment, they must guarantee to do so dependably, despite both physical faults (in hardware) and design faults (in hardware or software). A fault-tolerance approach is mandatory for these guarantees to be commensurate with the safety and reliability requirements of many life- and mission-critical applications. This book explains the motivations and the results of a collaborative project', whose objective was to significantly decrease the lifecycle costs of such fault tolerant systems. The end-user companies participating in this project already deploy fault-tolerant systems in critical railway, space and nuclear-propulsion applications. However, these are proprietary systems whose architectures have been tailored to meet domain-specific requirements. This has led to very costly, inflexible, and often hardware-intensive solutions that, by the time they are developed, validated and certified for use in the field, can already be out-of-date in terms of their underlying hardware and software technology.