| 11. |
- Aysan, Hüseyin, et al.
(författare)
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FT-Feasibility in Fixed Priority Real-Time Scheduling
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Real-time systems typically have to satisfy complex requirements mapped to the timing attributes of the tasks that are eventually guaranteed by the underlying scheduler. These systems consist of a mix of hard and soft tasks with varying criticalities as well as associated fault tolerance (FT) requirements. Often time redundancy techniques are preferred in many embedded applications and hence it is extremely important to devise appropriate methodologies for scheduling real-time tasks under fault assumptions. Additionally, the relative criticality of tasks could undergo changes during the evolution of the system. Hence scheduling decisions under fault assumptions have to reflect all these important factors in addition to the resource constraints.In this paper we propose a framework for 'FTfeasibility', i.e., to provide a priori guarantees that all critical tasks in the system will meet their deadlines even in case of faults. Our main objective here is to ensure FTfeasibility of all critical tasks in the system and do so with minimal costs and without any fundamental changes in the scheduling paradigm. We demonstrate its applicability in scenarios where the FT strategy employed is re-execution of the affected tasks or an alternate action upon occurrence of transient faults or software design faults. We analyse a feasible set of tasks and propose methods to adapt it to varying FT requirements without modifications to the underlying scheduler. We do so by reassigning task attributes to achieve FT-feasibility while keeping the costs minimised.
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| 12. |
- Aysan, Hüseyin, et al.
(författare)
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On Voting Strategies for Loosely Synchronized Dependable Real-Time Systems
- 2012
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Ingår i: 7th IEEE International Symposium on Industrial Embedded Systems. - 9781467326834 ; , s. 120-129
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Konferensbidrag (refereegranskat)abstract
- Hard real-time applications typically have to satisfy high dependability requirements in terms of fault tolerance in both the value and the time domains. Loosely synchronized real-time systems, which represent many of the systems that are developed, make any form of voting difficult as each replica may provide different outputs independent of whether there has been an error or not. This can also lead to false positives and false negatives which makes achieving fault tolerance, and hence dependability, difficult. We have earlier proposed a majority voting technique, ”Voting on Time and Value” (VTV) that explicitly considers combinations of value and timing errors, targeting loosely synchronised systems. In this paper, we extend VTV to enable voter parameter tuning to obtain the desired user specified trade-offs between the false positive and false negative rates in the voter outputs. We evaluate the performance of VTV against Compare Majority Voting (CMV), which is a known voting approach applicable in similar contexts, through extensive simulation studies. The results clearly demonstrate that VTV outperforms CMV in all scenarios with lower false negative rates.
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| 13. |
- Aysan, Hüseyin, et al.
(författare)
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Probabilistic schedulability analysis for fault tolerant tasks under stochastic error occurrences
- 2013
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Ingår i: 19th International Conference on Control Systems and Computer Science, CSCS 2013. ; , s. 113-120
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Konferensbidrag (refereegranskat)abstract
- In dependable real-time systems, provision of schedulability guarantees for task sets under realistic fault and error assumptions is an essential requirement, though complex and tricky to achieve. An important factor to be considered in this context is the random nature of occurrences of faults and errors, which, if addressed in the traditional schedulability analysis by assuming a rigid worst case occurrence scenario, may lead to inaccurate results. In this paper we first propose a stochastic fault and error model which has the capability of modeling error bursts in lieu of the commonly used simplistic error assumptions in processor scheduling. We then present a novel schedulability analysis that accounts for a range of worst case scenarios generated by stochastic error burst occurrences on the response times of tasks scheduled under the fixed priority scheduling (FPS) policy. Finally, we describe a methodology for the calculation of probabilistic schedulability guarantees as a weighted sum of the conditional probabilities of schedulability under specified error burst characteristics.
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| 14. |
- Aysan, Hüseyin, et al.
(författare)
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Probabilistic schedulability guarantees for dependable real-time systems under error bursts
- 2011
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Ingår i: Proc. 10th IEEE Int. Conf. on Trust, Security and Privacy in Computing and Communications, TrustCom 2011, 8th IEEE Int. Conf. on Embedded Software and Systems, ICESS 2011, 6th Int. Conf. on FCST 2011. - 9780769546001 ; , s. 1154-1163
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Konferensbidrag (refereegranskat)abstract
- The fundamental requirement for the design of effective and efficient fault-tolerance mechanisms in dependable real-time systems is a realistic and applicable model of potential faults, their manifestations and consequences. Fault and error models also need to be evolved based on the characteristics of the operational environments or even based on technological advances. In this paper we propose a probabilistic burst error model in lieu of the commonly used simplistic fault assumptions in the context of processor scheduling. We present a novel schedulability analysis that accounts for the worst case interference caused by error bursts on the response times of tasks scheduled under the fixed priority scheduling (FPS) policy. Further, we describe a methodology for the calculation of probabilistic schedulability guarantees as a weighted sum of the conditional probabilities of schedulability under specified error burst characteristics. Finally, we identify potential sources of pessimism in the worst case response time calculations and discuss potential means for circumventing these issues.
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| 15. |
- Aysan, Hüseyin, et al.
(författare)
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Probabilistic Scheduling Guarantees in Distributed Real-Time Systems under Error Bursts
- 2012
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Ingår i: IEEE Symposium on Emerging Technologies and Factory Automation, ETFA 2012. - 9781467347372 ; , s. Article number: 6489644-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Networked embedded systems used in many real-time (RT) applications rely on dependable communication. Controller Area Network (CAN) has gained wider acceptance as a standard in a large number of applications, mostly due to its cost effectiveness, predictable performance, and its fault-tolerance capability. Research so far has focused on rather simplistic error models which assume only singleton errors separated by a minimum inter-arrival time. However, these systems are often subject to faults that manifest as error bursts of various lengths which have an adverse effect on the message response times that needs to be accounted for. Furthermore, an important factor to be considered in this context is the random nature of occurrences of faults and errors, which, if addressed in the traditional schedulability analysis by assuming a rigid worst case occurrence scenario, may lead to inaccurate results. In this paper we first present a stochastic fault and error model which has the capability of modeling error bursts in lieu of the commonly used simplistic error assumptions. We then present a methodology which enables the provision of appropriate probabilistic RT guarantees in distributed RT systems for the particular case of message scheduling on CAN under the assumed error assumptions
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| 16. |
- Aysan, Huseyin, et al.
(författare)
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Schedulability guarantees for dependable distributed real-time systems under error bursts
- 2013
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Ingår i: Advances in Intelligent Systems and Computing. - Berlin, Heidelberg : Springer Verlag. - 9783642325472 ; , s. 393-406
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Konferensbidrag (refereegranskat)abstract
- In dependable embedded real-time systems, typically built of computing nodes exchanging messages over reliability-constrained networks, the provision of schedulability guarantees for task and message sets under realistic fault and error assumptions is an essential requirement, though complex and tricky to achieve. An important factor to be considered in this context is the random nature of occurrences of faults and errors, which, if addressed in the traditional schedulability analysis by assuming a rigid worst-case occurrence scenario, may lead to inaccurate results. In this work we propose a framework for end-to-end probabilistic schedulability analysis for real-time tasks exchanging messages over Controller Area Network under stochastic errors.
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| 17. |
- Aysan, Hüseyin, et al.
(författare)
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Task-Level Probabilistic Scheduling Guarantees for Dependable Real-Time Systems : A designer centric approach
- 2011
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Ingår i: Proceedings - 2011 14th IEEE International Symposium on Object/Component/Service-Oriented Real-Time Distributed Computing Workshops, ISORCW 2011. - 9780769543772 ; , s. 281-287
-
Konferensbidrag (refereegranskat)abstract
- Dependable real-time systems typically consist of tasks of mixed-criticality levels with associated fault tolerance (FT) requirements and scheduling them in a fault-tolerant manner to efficiently satisfy these requirements is a challenging problem. From the designers' perspective, the most natural way to specify the task criticalities is by expressing the reliability requirements at task level, without having to deal with low level decisions, such as deciding on which FT method to use, where in the system to implement the FT and the amount of resources to be dedicated to the FT mechanism. Hence, it is extremely important to devise methods for translating the highlevel requirement specifications for each task into the low-level scheduling decisions needed for the FT mechanism to function efficiently and correctly. In this paper, we focus achieving FT by redundancy in the temporal domain, as it is the commonly preferred method in embedded applications to recover from transient and intermittent errors, mainly due to its relatively low cost and ease of implementation. We propose a method which allows the system designer to specify task-level reliability requirements and provides a priori probabilistic scheduling guarantees for real-time tasks with mixed-criticality levels in the context of preemptive fixed-priority scheduling. We illustrate the method on a running example.
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| 18. |
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| 19. |
- Aysan, Hüseyin, et al.
(författare)
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VTV -- A Voting Strategy for Real-Time Systems
- 2008
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Ingår i: Proceedings of the 14th IEEE Pacific Rim International Symposium on Dependable Computing, PRDC 2008. - 9780769534480 ; , s. 56-63
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Konferensbidrag (refereegranskat)abstract
- Real-time applications typically have to satisfy high dependability requirements and require fault tolerance in both value and time domains. A widely used approach to ensure fault tolerance in dependable systems is the N-modular redundancy (NMR) which typically uses a majority voting mechanism. However, NMR primarily focuses on producing the correct value, without taking into account the time dimension. In this paper, we propose a new approach, Voting on Time and Value (VTV), applicable to real-time systems, which extends the modular redundancy approach by explicitly considering both value and timing failures, such that correct value is produced at a correct time, under specified assumptions. We illustrate our voting approach by instantiating it in the context of the well-known triple modular redundancy (TMR) approach. Further, we present a generalized version targeting NMR that enables a high degree of customization from the user perspective.
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| 20. |
- Buiu, C, et al.
(författare)
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GENESIS - A Framework for Global Engineering of Embedded Systems
- 2008
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Ingår i: Proceedings - International Conference on Software Engineering. - New York, NY, USA : ACM. - 9781605580760 ; , s. 87-93
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Konferensbidrag (refereegranskat)abstract
- GENESIS is an European initiative involving institutions and personsfrom older and new EU members, and West Balkan countries. It aims atdeveloping a global network of research and education in embeddedsystems. The related research will be coordinated in such a way toaddress hot topics at European and global levels and willconcentrate on the fusion of embedded systems and distributedservices over the Internet. One of the main objectives of GENESIS isto develop a distributed virtual laboratory to be used in embeddedsystems research and education and this is described in detail. Thispaper presents the rationale behind this initiative and the mainactions that are proposed to fulfill the educational, and scientificobjectives of GENESIS.
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