Replica determinism and flexible scheduling in hard real-time dependable systems

Fault-tolerant real-time systems are typically based on active replication where replicated entities are required to deliver their outputs in an identical order within a given time interval. Distributed scheduling of replicated tasks, however, violates this requirement if on-line scheduling, preemptive scheduling, or scheduling of dissimilar replicated task sets is employed. This problem of inconsistent task outputs has been solved previously by coordinating the decisions of the local schedulers such that replicated tasks are executed in an identical order. Global coordination results either in an extremely high communication effort to agree on each schedule decision or in an overly restrictive execution model where on-line scheduling, arbitrary preemptions, and nonidentically replicated task sets are not allowed. To overcome these restrictions, a new method, called timed messages, is introduced. Timed messages guarantee deterministic operation by presenting consistent message versions to the replicated tasks. This approach is based on simulated common knowledge and a sparse time base. Timed messages are very effective since they neither require communication between the local scheduler nor do they restrict usage of on-line flexible scheduling, preemptions and nonidentically replicated task sets

NASA Formal Methods Workshop, 1990

The workshop brought together researchers involved in the NASA formal methods research effort for detailed technical interchange and provided a mechanism for interaction with representatives from the FAA and the aerospace industry. The workshop also included speakers from industry to debrief the formal methods researchers on the current state of practice in flight critical system design, verification, and certification. The goals were: define and characterize the verification problem for ultra-reliable life critical flight control systems and the current state of practice in industry today; determine the proper role of formal methods in addressing these problems, and assess the state of the art and recent progress toward applying formal methods to this area

An Optimization Based Design for Integrated Dependable Real-Time Embedded Systems

Moving from the traditional federated design paradigm, integration of mixedcriticality software components onto common computing platforms is increasingly being adopted by automotive, avionics and the control industry. This method faces new challenges such as the integration of varied functionalities (dependability, responsiveness, power consumption, etc.) under platform resource constraints and the prevention of error propagation. Based on model driven architecture and platform based design’s principles, we present a systematic mapping process for such integration adhering a transformation based design methodology. Our aim is to convert/transform initial platform independent application specifications into post integration platform specific models. In this paper, a heuristic based resource allocation approach is depicted for the consolidated mapping of safety critical and non-safety critical applications onto a common computing platform meeting particularly dependability/fault-tolerance and real-time requirements. We develop a supporting tool suite for the proposed framework, where VIATRA (VIsual Automated model TRAnsformations) is used as a transformation tool at different design steps. We validate the process and provide experimental results to show the effectiveness, performance and robustness of the approach

Advanced information processing system: The Army fault tolerant architecture conceptual study. Volume 1: Army fault tolerant architecture overview

Digital computing systems needed for Army programs such as the Computer-Aided Low Altitude Helicopter Flight Program and the Armored Systems Modernization (ASM) vehicles may be characterized by high computational throughput and input/output bandwidth, hard real-time response, high reliability and availability, and maintainability, testability, and producibility requirements. In addition, such a system should be affordable to produce, procure, maintain, and upgrade. To address these needs, the Army Fault Tolerant Architecture (AFTA) is being designed and constructed under a three-year program comprised of a conceptual study, detailed design and fabrication, and demonstration and validation phases. Described here are the results of the conceptual study phase of the AFTA development. Given here is an introduction to the AFTA program, its objectives, and key elements of its technical approach. A format is designed for representing mission requirements in a manner suitable for first order AFTA sizing and analysis, followed by a discussion of the current state of mission requirements acquisition for the targeted Army missions. An overview is given of AFTA's architectural theory of operation

An analysis of the impact of governmental regulations on small business enterprises: a case study of Campbellton Plaza, 1987

The primary intent of this study is to examine the impact of governmental regulations on Small Business Enterprises located at the Campbellton Plaza. Campbellton Plaza is one of the fourteen commercial districts in Atlanta which has been targeted for revitalization by the City of Atlanta. The project is a joint venture operated by Southwest Economic Development Corporation, the Citizens and Southern National Bank, the Atlanta Economic Development Corporation, Georgia State University Small Business Program and the Bureau of Planning. The writer, through working with the small businesses and the city government at the Campbellton Plaza observed that the federal government as well as state and local municipalities played important roles by giving assistance to small business in several ways. For the merchants to be eligible for the needed assistance, they have to comply with several criteria, regulatory guidelines and deadline. Although this study is confined to the Campbellton Plaza, it is hoped that the study will contribute to a better understanding of the impacts of the governmental regulations on small business in general by the readers of this paper. This study was chosen because of constant complaints by the merchants about the criteria in getting the Business Improvement Loan Fund designated to the Campbellton Plaza. The data for this study were obtained from both primary and secondary sources, and the methodology employed is descriptive analysis

Distributed real-time fault tolerance in a virtualized separation kernel

Computers are increasingly being placed in scenarios where a computer error could result in the loss of human life or significant financial loss. Fault tolerant techniques must be employed to prevent an error from resulting in a fault causing such losses. Two types of errors that are common in real-time and embedded system are soft errors, i.e. data bit corruption, and timing errors, such as missed deadlines. Purely software based techniques to address these types of errors have the advantage of not requiring specialized hardware and are able to use more readily available commercial off-the-shelf hardware. Timing errors are addressed using Adaptive Mixed-Criticality, a scheduling technique where higher criticality tasks are given precedence over those of lower criticality when it is impossible to guarantee the schedulability of all tasks. While mixed-criticality scheduling has gained attention in recent years, most approaches assume a periodic task model and that the system has a single criticality level which dictates the available budget to all tasks. In practice these assumptions do not hold: different types of tasks are better served by different scheduling approaches and only a subset of high critical tasks might require additional capacity to meet deadlines. In the latter case, this occurs when a process has experienced a fault and requires additional capacity to perform the recovery. In this thesis, soft errors are addressed using a novel real-time fault tolerance method based on a virtualized separation kernel. Instead of executing redundant copies of an application on separate machines, the applications are consolidated onto one multi-core processor and use hardware virtualization extensions to partition the applications. This allows new recovery schemes to be explored. In addition, the maximum recovery time is sufficiently bounded to ensure recovery occurs in a timely manner without affecting the normal execution of the application. A virtualized separation kernel in combination with Adaptive Mixed-Criticality techniques creates a fault tolerant system that predictably detects and recovers from timing and soft errors

Scheduling Issues in Real-Time Systems

The most important objective of real-time systems is to fulfill time-critical missions in satisfying their application requirements and timing constraints. Software utilities can analyze real-time tasks and extract their characteristics and requirements for assisting the systems to guarantee schedulability. Real- time scheduling is the core of the real-time system design. It should allow real-time systems to exhibit predictable timing correctness regardless of possible uncertainty in run-time environments. In this dissertation, we study the problem of scheduling real-time tasks with resource and fault-tolerance requirements. For tasks with resource requirements, two types of platforms are examined: multiprocessor hard real-time systems and real-time database systems; for task with fault-tolerance requirements, we focus on hard real-time systems. We investigate preemptive priority-based scheduling for tasks with resource requirements in context of hard real-time systems. Rate-monotonic and earliest deadline first priority assignment strategies can meet deadlines if the schedulability conditions are satisfied. We propose resource control protocols, for these scheduling strategies, based on the concepts of priority inheritance and priority ceiling and describe schedulability conditions for meeting deadlines. Real-time database systems have different objectives for transaction scheduling. Minimizing miss ratio usually is the major concern. We study the significance of the knowledge of execution time in system performance and propose a class of optimistic concurrency control protocols using the knowledge of execution time. Our simulation results indicate that the knowledge of execution time substantially improve system performance. Fault-tolerance is an ability to maintain system in a safe and stable state such that the real-time application functions correctly and its timing constraints are satisfied even in the presence of faults. We develop a scheduling algorithm which attempts to build as many fault-tolerant tasks as possible into a schedule. We approximate system reliability by Markov chain models and illustrate the applicability of the proposed reliability models. We compare the proposed fault-tolerance scheduling approach with the basic fault-tolerance scheduling schemes and the simulation results show that our method provides better reliability than the basic scheduling schemes. (Also cross-referenced as UMIACS-TR-95-73

Avaliação do desempenho de redes PROFIBUS-DP suportada em técnicas de injecção de faltas

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200