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Real-Time Systems, 2006. 18th Euromicro Conference on

Date 5-7 July 2006

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  • 18th Euromicro Conference on Real-Time Systems

    Publication Year: 2006 , Page(s): c1
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  • 18th Euromicro Conference on Real-Time Systems - Title Page

    Publication Year: 2006 , Page(s): i - iii
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  • 18th Euromicro Conference on Real-Time Systems - Copyright

    Publication Year: 2006 , Page(s): iv
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  • 18th Euromicro Conference on Real-Time Systems - Table of contents

    Publication Year: 2006 , Page(s): v - vii
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  • Message from the Program Chair

    Publication Year: 2006 , Page(s): viii
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  • Program Committee

    Publication Year: 2006 , Page(s): ix
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  • A formal approach to multi-dimensional sensitivity analysis of embedded real-time systems

    Publication Year: 2006 , Page(s): 10 pp. - 12
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB) |  | HTML iconHTML  

    System robustness is a major concern in the design of efficient and reliable state-of-the-art heterogenous embedded real-time systems. Due to complex component interactions, resource sharing and functional dependencies, one-dimensional sensitivity analysis cannot cover all effects that modifications of one system property may have on system performance. One reason is that the variation of one property can also affect the values of other system properties requiring new approaches to keep track of simultaneous parameter changes. In this paper we present a heuristic and a stochastic approach suited for the multi-dimensional sensitivity analysis of large heterogenous embedded systems with complex timing constraints View full abstract»

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  • Sensitivity analysis for fixed-priority real-time systems

    Publication Year: 2006 , Page(s): 10 pp. - 22
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (355 KB) |  | HTML iconHTML  

    At early stages in the design of real-time embedded applications, the timing attributes of the computational activities are often incompletely specified or subject to changes. Later in the development cycle, schedulability analysis can be used to check the feasibility of the task set. However, the knowledge of the worst-case response times of tasks is often not sufficient to precisely determine the actions that would correct a non-schedulable design. In these situations, sensitivity analysis provides useful information for changing the implementation, by giving a measure of those computation times that must be reduced to achieve feasibility, or those that can be increased in case of a product extension, or providing the range of feasible periods for selecting the proper task activation rates. In this work, we exploit the concept of feasibility region to propose a faster and more concise solution to the sensitivity analysis problem with respect to existing techniques based on binary search. Furthermore, we show how the formalization of other problems in the feasibility domain, such as managing overloads through elastic scheduling, can be extended to the exact analysis View full abstract»

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  • Clairvoyant non-preemptive EDF scheduling

    Publication Year: 2006 , Page(s): 7 pp. - 32
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB) |  | HTML iconHTML  

    It is well-known that although EDF is optimal for preemptive systems this is not the case in non-preemptive ones. The problem is that for a non-preemptive scheduler to be optimal, it must sometimes use inserted idle times. In this paper we show how the performance of non-preemptive EDF can be improved by using a form of lookahead that identifies when idle time insertion is necessary. Experiments show that this modification increases the number of schedulable task sets by up to 100%. Furthermore, by using a form of lazy evaluation the algorithm runs in O(nlog n) which is the same as plain EDF View full abstract»

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  • Design and performance of a fault-tolerant real-time CORBA event service

    Publication Year: 2006 , Page(s): 10 pp. - 42
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB) |  | HTML iconHTML  

    Developing distributed real-time and embedded (DRE) systems in which multiple quality-of-service (QoS) dimensions must be managed is an important and challenging problem. This paper makes three contributions to research on multi-dimensional QoS for DRE systems. First, it describes the design and implementation of a fault-tolerant real-time CORBA event service for the ACE ORB (TAO). Second, it describes our enhancements and extensions to features in TAO, to integrate real-time and fault tolerance properties. Third, it presents an empirical evaluation of our approach. Our results show that with some refinements, real-time and fault-tolerance features can be integrated effectively and efficiently in a CORBA event service View full abstract»

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  • Real-time multi-agent support for decentralized management of electric power

    Publication Year: 2006 , Page(s): 9 pp. - 51
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB) |  | HTML iconHTML  

    Establishing clean or renewable energy sources involves the problem of adequate management for the networked power sources, in particular since producers are at the same time also consumers, and vice versa. We describe the first phases of the joint R&D project DEZENT between the School of Computer Science and the College of Electrical Engineering at the University of Dortmund, devoted to decentralized and adaptive electric power management through a distributed real-time multi-agent architecture. Unpredictable consumer requests or producer problems, under distributed control or local autonomy will be the major novelty. We present a distributed real-time negotiation algorithm involving agents on different levels of negotiation, on behalf of producers and consumers of electric energy. Despite the lack of global overview we are able to prove that in our model no coalition of malicious users could take advantage of extreme situations like arising from an abundance as much as from any (artificial) shortage of electric power that are typical problems in "free" or deregulated markets. Our multi-agent system exhibits a very high robustness against power failures compared to centrally controlled architectures. In extensive experiments we demonstrate how, in realistic settings of the German power system structure, the novel algorithms can cope with unforeseen needs and production specifics in a very flexible and adaptive way, taking care of most of the potentially hard deadlines already on the local group level (corresponding to a small subdivision). We further demonstrate that under our decentralized approach customers pay less than under any conventional (global) management policy or structure View full abstract»

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  • The dependency management framework: a case study of the ION CubeSat

    Publication Year: 2006 , Page(s): 10 pp. - 64
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (429 KB) |  | HTML iconHTML  

    Due to the complexity and requirements of modern realtime systems, multiple teams must often work concurrently and independently to develop the various components of the system. Since a team typically only knows the dependency relations between the components they wrote and those they directly use, keeping track of system-wide dependency relations is not possible for any individual team. To further complicate matters, dependency relations often change as software components are refined or their interactions modified. Because the robustness of any real-time system hinges on the availability of essential services in spite of faults and failures in useful but non-essential components, keeping track of the constantly evolving dependency relations between the system's components is crucial. If a system's designers cannot ensure that critical services only USE but do not DEPEND ON less critical components, a seemingly minor fault can propagate along complex and unforeseen dependency chains and bring down the entire system. Therefore, automatically tracking and analyzing system-wide dependency relations given only local dependency information is vital for the development of robust real time systems. This paper presents DMF (dependency management framework), a prototype toolkit for dependency management in designing robust real-time systems. We demonstrate the usability and scalability of DMF with a case study of ION CubeSat, the University of Illinois at Urbana-Champaign 's first student-developed satellite View full abstract»

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  • Optimal deadline assignment for periodic real-time tasks in dynamic priority systems

    Publication Year: 2006 , Page(s): 10 pp. - 74
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6876 KB) |  | HTML iconHTML  

    Real-time systems are often designed using a set of periodic tasks. Task periods are usually set by the system requirements, but deadlines and computation times can be modified in order to improve system performance. Sensitivity analysis in real-time systems has focused on changes in task computation times using fixed priority analysis. Only a few studies deal with the modification of deadlines in dynamic priority scheduling. The aim of this work is to provide a sensitivity analysis for task deadlines in the context of dynamic-priority, pre-emptive, uniprocessor scheduling. In this paper, we present a deadline minimisation method that achieves the maximum reduction. As undertaken in other studies concerning computation times, we also define and calculate the critical scaling factor for task deadlines. Our proposal is evaluated and compared with other works in terms of jitter. The deadline minimisation can be used to strongly reduce jitter of control tasks, in a real-time control application View full abstract»

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  • Efficient synchronization under global EDF scheduling on multiprocessors

    Publication Year: 2006 , Page(s): 10 pp. - 84
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB) |  | HTML iconHTML  

    We consider coordinating accesses to shared data structures in multiprocessor real-time systems scheduled under preemptive global EDF. To our knowledge, prior work on global EDF has focused only on systems of independent tasks. We take an initial step here towards a generic resource-sharing framework by considering simple shared objects, such as queues, stacks, and linked lists. In many applications, the predominate use of synchronization constructs is for sharing such simple objects. We analyze two synchronization methods for such objects, one based on queue-based spin locks and a second based on lock-free algorithms View full abstract»

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  • The feasibility analysis of multiprocessor real-time systems

    Publication Year: 2006 , Page(s): 10 pp. - 96
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB) |  | HTML iconHTML  

    The multiprocessor scheduling of collections of real-time jobs is considered. Sufficient tests are derived for determining whether a given collection of jobs can be scheduled to meet all deadlines upon a specified multiprocessor platform - these tests may be applied even when the collection of jobs is incompletely specified. The applicability of these tests to the scheduling of collections of jobs that are generated by systems of recurrent real-time tasks is discussed View full abstract»

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  • Hierarchical event streams and event dependency graphs: a new computational model for embedded real-time systems

    Publication Year: 2006 , Page(s): 10 pp. - 106
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (403 KB) |  | HTML iconHTML  

    One of the important aspects of schedulability analysis is the model used to describe the system and its timing behavior. On one side, the accuracy of the test strongly depends on the accuracy of the model. On the other side, a detailed model could lead to an unaccaptable evaluation time. In this paper we propose a new model, the hierarchical event streams, which allows a high accuracy. We provide an efficient feasibility test for the model based on the context of demand and request bound function. Additionally we will provide a methodology to extract this model out of a control-flow graph efficiently. Together this allows a more accurate and efficient schedulability analysis of event driven real-time systems View full abstract»

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  • On a theory of media processing systems behavior, with applications

    Publication Year: 2006 , Page(s): 11 pp. - 117
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB) |  | HTML iconHTML  

    In this article we provide a model for the dynamic behavior of media processing chains of tasks communicating via bounded buffers. The aim is to find the overall behavior of a chain from which performance parameters (such as start time and response time of individual tasks, chain end-to-end response time, number of context switches and resource utilization) follow. This behavior is characterized in terms of the elementary actions of the tasks that make up the chain. From this we derive corollaries that give design guidelines, supporting the goal of improving chain end-to-end response time and the optimization of resources, which is achieved by minimizing context-switching overhead and buffer sizes View full abstract»

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  • The partitioned scheduling of sporadic tasks according to static-priorities

    Publication Year: 2006 , Page(s): 10 pp. - 127
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    A polynomial-time algorithm is presented for partitioning a collection of sporadic tasks among the processors of an identical multiprocessor platform with static-priority scheduling on each individual processor. Since the partitioning problem is easily seen to be NP-hard in the strong sense, this algorithm is not optimal. A quantitative characterization of its worst-case performance is provided in terms of sufficient conditions and resource augmentation approximation bounds. The partitioning algorithm is also evaluated over randomly generated task systems View full abstract»

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  • Task reweighting under global scheduling on multiprocessors

    Publication Year: 2006 , Page(s): 11 pp. - 140
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (417 KB) |  | HTML iconHTML  

    We consider schemes for enacting task share changes - a process called reweighting - on real-time multiprocessor platforms. Our particular focus is reweighting schemes that are deployed in environments in which tasks may frequently request significant share changes. Prior work has shown that fair scheduling algorithms are capable of reweighting tasks with minimal allocation error and that partitioning-based scheduling algorithms can reweight tasks with better average-case performance, but greater error. However, preemption and migration overheads can be high in fair schemes. In this paper, we consider the question of whether global scheduling techniques can improve the accuracy of reweighting relative to partitioning-based schemes and provide improved average-case performance relative to fair-scheduled systems. Our conclusion is that, for soft real-time systems, global scheduling techniques provide a good mix of accuracy and average-case performance View full abstract»

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  • Optimal on-line scheduling of multiple control tasks: a case study

    Publication Year: 2006 , Page(s): 10 pp. - 150
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (406 KB) |  | HTML iconHTML  

    We study the problem of dynamically scheduling a set of state-feedback control tasks controlling a set of linear plants. We consider an on-line non-preemptive scheduling policy that is optimal in the sense that it minimizes a quadratic performance criterion for the overall system. The optimal scheduling decision at each point in time is a function of the states of the controlled plants. To be able to solve the scheduling problem for realistic examples, we use the technique of relaxed dynamic programming to compute suboptimal solutions with error bounds. The approach is compared to earlier approaches in a case study involving simultaneous control of one ball-and-beam process and two DC-servo processes. We also show how the scheduling policy can be modified to allow for background tasks to execute when the need for control is small View full abstract»

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  • Hierarchical control of multiple resources in distributed real-time and embedded systems

    Publication Year: 2006 , Page(s): 10 pp. - 160
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    There is an increasing demand to introduce adaptive capabilities in distributed real-time and embedded (DRE) systems that execute in open environments where system operational conditions, input workload, and resource availability cannot be characterized accurately a priori. To meet these needs, this paper presents the hierarchical distributed resource-management architecture (HiDRA), which provides adaptive resource management using control-the ore tic techniques that adapt to workload fluctuations and resource availability. In contrast to adaptive control techniques that manage only one type of system resource, HiDRA features a hierarchical control scheme that manages both bandwidth and processor utilization simultaneously. This paper presents three contributions to research in adaptive resource management for DRE systems. First, we describe the structure and functionality of HiDRA. Second, we present an analytical model of HiDRA that formalizes its control theoretic behavior and present analytical performance guarantees. Third, we evaluate the performance of HiDRA via experiments on a representative DRE system that performs distributed target tracking in real-time. Our analytical and empirical results indicate that HiDRA yields predictable, stable, and high system performance, even in the face of changing workload View full abstract»

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  • Reactive speed control in temperature-constrained real-time systems

    Publication Year: 2006 , Page(s): 10 pp. - 170
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB) |  | HTML iconHTML  

    In this paper, we study temperature-constrained real-time systems, where real-time guarantees must be met without exceeding safe temperature levels within the processor. We give a short review on temperature issues in processors and describe how speed control can be used to trade-off task delays against processor temperature. In this paper, we describe how traditional worst-case execution scenarios do not apply in temperature-constrained situations. As example, we adopt a simple reactive speed control technique. We show how this simple reactive scheme can improve the processor utilization compared with any constant-speed scheme View full abstract»

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  • Resource management for control tasks based on the transient dynamics of closed-loop systems

    Publication Year: 2006 , Page(s): 10 pp. - 182
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (878 KB) |  | HTML iconHTML  

    This paper presents a resource management strategy for control tasks that maximizes control performance within the available resources by readjusting the task periods at runtime. A feedback scheduler is used to determine on-line the optimal task periods considering the response over a finite time horizon of the plants controlled by arbitrary linear control laws. We show how this problem can be expressed as an optimization problem, where the objective function relates the sampling periods to the transient responses of the controlled plants, and where restrictions are based on EDF schedulability constraints. For the general case, the solution of the optimization problem is computationally expensive, and thus, an approximate procedure to be executed on-line has been developed. We present simulation results that validate the presented approach View full abstract»

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  • i-GAME: an implicit GTS allocation mechanism in IEEE 802.15.4 for time-sensitive wireless sensor networks

    Publication Year: 2006 , Page(s): 10 pp. - 192
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1544 KB) |  | HTML iconHTML  

    The IEEE 802.15.4 medium access control (MAC) protocol is an enabling technology for time sensitive wireless sensor networks thanks to its guaranteed-time slot (GTS) mechanism in the beacon-enabled mode. However, the protocol only supports explicit GTS allocation, i.e. a node allocates a number of time slots in each superframe for exclusive use. The limitation of this explicit GTS allocation is that GTS resources may quickly disappear, since a maximum of seven GTSs can be allocated in each superframe, preventing other nodes to benefit from guaranteed service. Moreover, the GTSs may be only partially used, resulting in wasted bandwidth. To overcome these limitations, this paper proposes i-GAME, an implicit GTS allocation mechanism in beacon-enabled IEEE 802.15.4 networks. The allocation is based on implicit GTS allocation requests, taking into account the traffic specifications and the delay requirements of the flows. The i-GAME approach enables the use of a GTS by multiple nodes, while all their (delay, bandwidth) requirements are still satisfied. For that purpose, we propose an admission control algorithm that enables to decide whether to accept a new GTS allocation request or not, based not only on the remaining time slots, but also on the traffic specifications of the flows, their delay requirements and the available bandwidth resources. We show that our proposal improves the bandwidth utilization compared to the explicit allocation used in the IEEE 802.15.4 protocol standard. We also present some practical considerations for the implementation of i-GAME, ensuring backward compatibility with the IEEE 801.5.4 standard with only minor add-ons View full abstract»

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