| 1. |
- Aysan, Hüseyin, et al.
(författare)
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Efficient Fault Tolerant Scheduling on Controller Area Network (CAN)
- 2010
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Ingår i: Proceedings of the 15th IEEE International Conference on Emerging Technologies and Factory Automation, ETFA 2010. - Bilbao, Spain. ; , s. Art.nr 5641318-
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Konferensbidrag (refereegranskat)abstract
- Dependable communication is becoming a critical factor due to the pervasive usage of networked embedded systems that increasingly interact with human lives in many real-time applications. Controller Area Network (CAN) has gained wider acceptance as a standard in a large number of industrial applications, mostly due to its efficient bandwidth utilization, ability to provide real-time guarantees, as well as its fault-tolerant capability. However, the native CAN fault-tolerant mechanism assumes that all messages transmitted on the bus are equally critical, which has an adverse impact on the message latencies, results in the inability to meet user defined reliability requirements, and, in some cases, even leads to violation of timing requirements. As the network potentially needs to cater to messages of multiple criticality levels (and hence varied redundancy requirements), scheduling them in an efficient fault-tolerant manner becomes an important research issue. We propose a methodology which enables the provision of appropriate guarantees in CAN scheduling of messages with mixed criticalities. The proposed approach involves definition of fault-tolerant feasibility windows of execution for critical messages, and off-line derivation of optimal message priorities that fulfill the user specified level of fault-tolerance.
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| 2. |
- Aysan, Hüseyin, 1982-
(författare)
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Fault-Tolerance Strategies and Probabilistic Guarantees for Real-Time Systems
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ubiquitous deployment of embedded systems is having a substantial impact on our society, since they interact with our lives in many critical real-time applications. Typically, embedded systems used in safety or mission critical applications (e.g., aerospace, avionics, automotive or nuclear domains) work in harsh environments where they are exposed to frequent transient faults such as power supply jitter, network noise and radiation. They are also susceptible to errors originating from design and production faults. Hence, they have the design objective to maintain the properties of timeliness and functional correctness even under error occurrences. Fault-tolerance plays a crucial role towards achieving dependability, and the fundamental requirement for the design of effective and efficient fault-tolerance mechanisms is a realistic and applicable model of potential faults and their manifestations. An important factor to be considered in this context is the random nature of faults and errors, which, if addressed in the timing analysis by assuming a rigid worst-case occurrence scenario, may lead to inaccurate results. It is also important that the power, weight, space and cost constraints of embedded systems are addressed by efficiently using the available resources for fault-tolerance. This thesis presents a framework for designing predictably dependable embedded real-time systems by jointly addressing the timeliness and the reliability properties. It proposes a spectrum of fault-tolerance strategies particularly targeting embedded real-time systems. Efficient resource usage is attained by considering the diverse criticality levels of the systems' building blocks. The fault-tolerance strategies are complemented with the proposed probabilistic schedulability analysis techniques, which are based on a comprehensive stochastic fault and error model.
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| 3. |
- Aysan, Hüseyin, et al.
(författare)
-
Fault Tolerant Scheduling on Control Area Network (CAN) :
- 2010
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Ingår i: ISORC Workshops 2010 - 2010 13th IEEE International Symposium on Object/Component/Service-Oriented Real-Time Distributed Computing Workshops, Vol. 2. ; , s. 226-232
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Konferensbidrag (refereegranskat)abstract
- Dependable communications is becoming a critical factor due to the pervasive usage of networked embedded systems that increasingly interact with human lives in one way or the other in many real-time applications. Though many smaller systems are providing dependable services employing uniprocesssor solutions, stringent fault containment strategies etc., these practices are fast becoming inadequate due to the prominence of COTS in hardware and component based development(CBD) in software as well as the increased focus on building 'system of systems'. Hence the repertoire of design paradigms, methods and tools available to the developers of distributed real-time systems needs to be enhanced in multiple directions and dimensions. In future scenarios, potentially a network needs to cater to messages of multiple criticality levels (and hence varied redundancy requirements) and scheduling them in a fault tolerant manner becomes an important research issue. We address this problem in the context of Controller Area Network (CAN), which is widely used in automotive and automation domains, and describe a methodology which enables the provision of appropriate scheduling guarantees. The proposed approach involves definition of fault-tolerant windows of execution for critical messages and the derivation of message priorities based on earliest deadline first (EDF).
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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-
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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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| 8. |
- 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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| 9. |
- 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
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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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| 10. |
- Chandran, Senthil Kumar, et al.
(författare)
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Efficient scheduling with adaptive fault tolerance in heterogeneous multiprocessor systems
- 2010
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Ingår i: International Conference on Computer and Electrical Engineering (ICCEE). - Chengdu, China.
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Konferensbidrag (refereegranskat)abstract
- Heterogeneous multiprocessor systems are becoming more common and scheduling real-time tasks on them is an extremely challenging research problem. While the stringent functional and timing requirements are to be met, this problem becomes even more difficult in dynamic environments, for example, caused by processor failures. Furthermore, in safety critical applications having tasks with mixed criticality levels, guaranteeing adaptive fault tolerance to meet the reliability requirements adds another complex dimension. The key contribution of our research is a framework for task allocation and scheduling in the above context, which has a generic task model enabling task-level redundancy, a range of reconfiguration/task migration options during processor failures and definition of a set of performance metrics. We have addressed the issues of both timeliness and reliability under three different allocation strategies for a multiprocessor system with the feasibility check being performed using the well-known Rate Monotonic (RM) schedulability test. The algorithm presented in this paper, ensures that all required deadlines are met with efficient processor utilization under normal conditions and guarantees essential operations even during processor failures. In real-time multiprocessor systems used in safety critical applications, the proposed approach is expected to provide better utilization of resources and guarantees with respect to the system reliability. We demonstrate as well as evaluate the performance of our approach by simulation studies on task scheduling in heterogeneous multiprocessor environments.
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