A hard real-time system is usually subject to stringent reliability and timing constraints since failure to produce correct results in a timely manner may lead to a disaster. One way to avoid missing deadlines is to t...
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A hard real-time system is usually subject to stringent reliability and timing constraints since failure to produce correct results in a timely manner may lead to a disaster. One way to avoid missing deadlines is to trade the quality of computation results for timeliness and software fault tolerance is often achieved with the use of redundant programs. A deadline mechanism which combines these two methods is proposed to provide software fault tolerance in hard real-time periodic task systems. Specifically, we consider the problem of scheduling a set of real-time periodic tasks each of which has two versions: primary and alternate. The primary version contains more functions (thus more complex) and produces good quality results, but its correctness is more difficult to verify because of its high level of complexity and resource usage. By contrast, the alternate version contains only the minimum required functions (thus simpler) and produces less precise, but acceptable results and its correctness is easy to verify. We propose a scheduling algorithm which 1) guarantees either the primary or alternate version of each critical task to be completed in time and 2) attempts to complete as many primaries as possible. Our basic algorithm uses a fixed priority-driven preemptive scheduling scheme to preallocate time intervals to the alternates and, at runtime, attempts to execute primaries first. An alternate will be executed only 1) if its primary fails due to lack of time or manifestation of bugs or 2) when the latest time to start execution of the alternate without missing the corresponding task deadline is reached. This algorithm is shown to be effective and easy to implement. this algorithm is enhanced further to prevent early failures in executing primaries from triggering failures in the subsequent job executions, thus improving efficiency of processor usage.
In industrial production, pipe plugging occurs in the process of pipeline conveying fluid. In this paper, different flow types such as laminar flow, bubble flow and core flow appear in the pipeline, and different numb...
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ISBN:
(纸本)9781538670361
In industrial production, pipe plugging occurs in the process of pipeline conveying fluid. In this paper, different flow types such as laminar flow, bubble flow and core flow appear in the pipeline, and different number of electrodes are designed to be actuated on the outer wall of the pipeline. Images of different flow types of images are reconstructed based on eit algorithm. Image reconstruction is evaluated based on the quality reconstruction function method. The experimental results show that the algorithm is effective and practical for image reconstruction of different flow patterns in pipelines.
Fault tolerance is an important aspect of real-time control systems, due to unavoidable timing constraints. In this paper, the timing problem of a set of concurrent periodic tasks is considered where each task has pri...
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ISBN:
(纸本)9781424441549
Fault tolerance is an important aspect of real-time control systems, due to unavoidable timing constraints. In this paper, the timing problem of a set of concurrent periodic tasks is considered where each task has primary and alternate versions. In the literature, probability of fault in the alternate version of a task is assumed to be zero. Here, a fault probability with uniform distribution has been used. In addition, to cover the situations in which both versions are scheduled with some time overlapping, a criterion is defined for prioritizing primary version against the alternate version. A new scheduling algorithm is proposed based on the defined criterion. Simulation results show that an increase in the number of executed primary tasks which improves the efficiency of processor utilization, hence prove the efficiency of the proposed algorithm.
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