1,282 research outputs found
Replication and fault-tolerance in real-time systems
PhD ThesisThe increased availability of sophisticated computer hardware and the corresponding
decrease in its cost has led to a widespread growth in the use of computer systems for realtime
plant and process control applications. Such applications typically place very high
demands upon computer control systems and the development of appropriate control
software for these application areas can present a number of problems not normally
encountered in other applications.
First of all, real-time applications must be correct in the time domain as well as the value
domain: returning results which are not only correct but also delivered on time. Further,
since the potential for catastrophic failures can be high in a process or plant control
environment, many real-time applications also have to meet high reliability requirements.
These requirements will typically be met by means of a combination of fault avoidance and
fault tolerance techniques.
This thesis is intended to address some of the problems encountered in the provision of fault
tolerance in real-time applications programs. Specifically,it considers the use of replication
to ensure the availability of services in real-time systems. In a real-time environment,
providing support for replicated services can introduce a number of problems. In particular,
the scope for non-deterministic behaviour in real-time applications can be quite large and
this can lead to difficultiesin maintainingconsistent internal states across the members of a
replica group. To tackle this problem, a model is proposed for fault tolerant real-time
objects which not only allows such objects to perform application specific recovery
operations and real-time processing activities such as event handling, but which also allows
objects to be replicated. The architectural support required for such replicated objects is
also discussed and, to conclude, the run-time overheads associated with the use of such
replicated services are considered.The Science and Engineering Research Council
Fault-Injection-Based Assessment of Fail-Silence Provided by Process Duplication versus Internal Error Detection in Scientific-Based Applications
Coordinated Science Laboratory was formerly known as Control Systems Laborator
Constructing fail-controlled nodes for distributed systems: a software approach
PhD ThesisDesigning and implementing distributed systems which continue to provide specified services
in the presence of processing site and communication failures is a difficult task. To facilitate
their development, distributed systems have been built assuming that their underlying hardware
components are Jail-controlled, i.e. present a well defined failure mode. However, if conventional
hardware cannot provide the assumed failure mode, there is a need to build processing sites
or nodes, and communication infra-structure that present the fail-controlled behaviour assumed.
Coupling a number of redundant processors within a replicated node is a well known way
of constructing fail-controlled nodes. Computation is replicated and executed simultaneously at
each processor, and by employing suitable validation techniques to the outputs generated by processors
(e.g. majority voting, comparison), outputs from faulty processors can be prevented from
appearing at the application level.
One way of constructing replicated nodes is by introducing hardwired mechanisms to
couple replicated processors with specialised validation hardware circuits. Processors are tightly
synchronised at the clock cycle level, and have their outputs validated by a reliable validation
hardware. Another approach is to use software mechanisms to perform synchronisation of processors
and validation of the outputs. The main advantage of hardware based nodes is the minimum
performance overhead incurred. However, the introduction of special circuits may increase
the complexity of the design tremendously. Further, every new microprocessor architecture requires
considerable redesign overhead. Software based nodes do not present these problems, on
the other hand, they introduce much bigger performance overheads to the system.
In this thesis we investigate alternative ways of constructing efficient fail-controlled, software
based replicated nodes. In particular, we present much more efficient order protocols, which
are necessary for the implementation of these nodes. Our protocols, unlike others published to
date, do not require processors' physical clocks to be explicitly synchronised. The main contribution
of this thesis is the precise definition of the semantics of a software based Jail-silent node,
along with its efficient design, implementation and performance evaluation.The Brazilian National Research Council (CNPq/Brasil)
Design of automotive X-by-Wire systems
http://www.taylorandfrancis.com/X-by-Wire is a generic term referring to the replacement of mechanical or hydraulic systems, such as braking or steering, by electronic ones. In this chapter, we analyze the real-time and dependability constraints of X-by-Wire systems, review the fault-tolerant services that are needed and the communication protocols (TTP/C, FlexRay and TTCAN) considered for use in such systems. Using a Steer-by-Wire case-study, we detail the design principles and verification methods that can be used to ensure the stringent constraints of X-by-Wire systems
Report of the Advisory Committee on the Future of the US Space Program
The United States' civil space program was rather hurriedly formulated some three decades ago on the heels of the successful launch of the Soviet Sputnik. A dozen humans have been placed on the Moon and safely returned to Earth, seven of the other eight planets have been viewed at close range, including the soft landing of two robot spacecraft on Mars, and a variety of significant astronomical and other scientific observations have been accomplished. Closer to Earth, a network of communications satellites has been established, weather and ocean conditions are now monitored and reported as they occur, and the Earth's surface is observed from space to study natural resources and detect sources of pollution. Problems and perspectives of the program are given as seen by the committee. The committee finds that there are nine concerns about the space program which are deserving of attention. The responsibilities of the agency are given. The space agenda becomes one of what can and should the U.S. afford for its space program. Also given is a concept of what the committee believes is a balanced space program. The programs international role is defined and some final observations and recommendations are made
Proceedings of the 5th International Workshop on Reconfigurable Communication-centric Systems on Chip 2010 - ReCoSoC\u2710 - May 17-19, 2010 Karlsruhe, Germany. (KIT Scientific Reports ; 7551)
ReCoSoC is intended to be a periodic annual meeting to expose and discuss gathered expertise as well as state of the art research around SoC related topics through plenary invited papers and posters. The workshop aims to provide a prospective view of tomorrow\u27s challenges in the multibillion transistor era, taking into account the emerging techniques and architectures exploring the synergy between flexible on-chip communication and system reconfigurability
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