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  • 1.
    Altenbernd, Peter
    et al.
    University of Applied Sciences, Germany.
    Gustafsson, Jan
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Lisper, Björn
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Stappert, Friedhelm
    Siemens VDO Automotive AG, Germany.
    Early execution time-estimation through automatically generated timing models2016Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 52, nr 6, s. 731-760Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Traditional timing analysis, such as worst-case execution time analysis, is normally applied only in the late stages of embedded system software development, when the hardware is available and the code is compiled and linked. However, preliminary timing estimates are often needed in early stages of system development as an essential prerequisite for the configuration of the hardware setup and dimensioning of the system. During this phase the hardware is often not available, and the code might not be ready to link. This article describes an approach to predict the execution time of software through an early, source-level timing analysis. A timing model for source code is automatically derived from a given combination of hardware architecture and compiler. The model is identified from measured execution times for a set of synthetic training programs, compiled for the hardware platform in question. It can be used to estimate the execution time for code running on the platform: the estimation is then done directly from the source code, without compiling and running it. Our experiments show that, using this model, we can predict the execution times of the final, compiled code surprisingly well. For instance, we achieve an average deviation of 8 % for a set of benchmark programs for the ARM7 architecture.

  • 2.
    Ashjaei, Mohammad
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Khalilzad, Nima
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Mubeen, Saad
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. IS (Embedded Systems).
    Behnam, Moris
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Sander, Ingo
    Royal Institute of Technology, Sweden.
    Almeida, Luis
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Designing End-to-end Resource Reservations in Predictable Distributed Embedded Systems2017Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 53, nr 6, s. 916-956Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Contemporary distributed embedded systems in many domains have become highly complex due to ever-increasing demand on advanced computer controlled functionality. The resource reservation techniques can be effective in lowering the software complexity, ensuring predictability and allowing flexibility during the development and execution of these systems. This paper proposes a novel end-to-end resource reservation model for distributed embedded systems. In order to support the development of predictable systems using the proposed model, the paper provides a method to design resource reservations and an end-to-end timing analysis. The reservation design can be subjected to different optimization criteria with respect to runtime footprint, overhead or performance. The paper also presents and evaluates a case study to show the usability of the proposed model, reservation design method and end-to-end timing analysis. 

  • 3.
    Ashjaei, Mohammad
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Patti, Gaetano
    University of Catania, Italy.
    Behnam, Moris
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Alderisi, Giuliana
    University of Catania, Italy.
    Lo Bello, Lucia
    University of Catania, Italy.
    Schedulability Analysis of Ethernet Audio Video Bridging Networks with Scheduled Traffic Support2017Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 53, nr 4, s. 526-577Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The IEEE Audio Video Bridging (AVB) technology is nowadays under consideration in several automation domains, such as, automotive, avionics, and industrial communications. AVB offers several benefits, such as open specifications, the existence of multiple providers of electronic components, and the real-time support, as AVB provides bounded latency to real-time traffic classes. In addition to the above mentioned properties, in the automotive domain, comparing with the existing in-vehicle networks, AVB offers significant advantages in terms of high bandwidth, significant reduction of cabling costs, thickness and weight, while meeting the challenging EMC/EMI requirements. Recently, an improvement of the AVB protocol, called the AVB ST, was proposed in the literature, which allows for supporting scheduled traffic, i.e., a class of time-sensitive traffic that requires time-driven transmission and low latency. In this paper, we present a schedulability analysis for the real-time traffic crossing through the AVB ST network. In addition, we formally prove that, if the bandwidth in the network is allocated according to the AVB standard, the schedulability test based on response time analysis will fail for most cases even if, in reality, these cases are schedulable. In order to provide guarantees based on analysis test a bandwidth over-reservation is required. In this paper, we propose a solution to obtain a minimized bandwidth over-reservation. To the best of our knowledge, this is the first attempt to formally spot the limitation and to propose a solution for overcoming it. The proposed analysis is applied to both the AVB standard and the AVB ST. The analysis results are compared with the results of several simulative assessments, obtained using OMNeT++, on both automotive and industrial case studies. The comparison between the results of the analysis and the simulation ones shows the effectiveness of the analysis proposed in this work.

  • 4.
    Bril, Reinder J.
    et al.
    Technische Universiteit Eindhoven, Netherlands .
    Lukkien, Johan
    Technische Universiteit Eindhoven, Netherlands .
    Verhaegh, Wim F.J.
    Philips Research Laboratories, Netherlands .
    Worst-case response time analysis of real-time tasks under fixed-priority scheduling with deferred preemption2009Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 42, nr 1-3, s. 63-119Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fixed-priority scheduling with deferred preemption (FPDS) has been proposed in the literature as a viable alternative to fixed-priority pre-emptive scheduling (FPPS), that obviates the need for non-trivial resource access protocols and reduces the cost of arbitrary preemptions. This paper shows that existing worst-case response time analysis of hard real-time tasks under FPDS, arbitrary phasing and relative deadlines at most equal to periods is pessimistic and/or optimistic. The same problem also arises for fixed-priority non-pre-emptive scheduling (FPNS), being a special case of FPDS. This paper provides a revised analysis, resolving the problems with the existing approaches. The analysis is based on known concepts of critical instant and busy period for FPPS. To accommodate for our scheduling model for FPDS, we need to slightly modify existing definitions of these concepts. The analysis assumes a continuous scheduling model, which is based on a partitioning of the timeline in a set of non-empty, right semi-open intervals. It is shown that the critical instant, longest busy period, and worst-case response time for a task are suprema rather than maxima for all tasks, except for the lowest priority task. Hence, that instant, period, and response time cannot be assumed for any task, except for the lowest priority task. Moreover, it is shown that the analysis is not uniform for all tasks, i.e. the analysis for the lowest priority task differs from the analysis of the other tasks. These anomalies for the lowest priority task are an immediate consequence of the fact that only the lowest priority task cannot be blocked. To build on earlier work, the worst-case response time analysis for FPDS is expressed in terms of known worst-case analysis results for FPPS. The paper includes pessimistic variants of the analysis, which are uniform for all tasks, illustrates the revised analysis for an advanced model for FPDS, where tasks are structured as flow graphs of subjobs rather than sequences, and shows that our analysis is sustainable.

  • 5.
    Chetto, Maryline
    et al.
    Univ Nantes, Nantes, France..
    Sjödin, Mikael
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. Malardalen Univ, Vasteras, Sweden..
    Guest editorial: special issue on the Real-Time and Network Systems (RTNS 2009) conference2010Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 46, nr 3, s. 303-304Artikkel i tidsskrift (Annet vitenskapelig)
  • 6.
    Davis, Rob
    et al.
    University of York, York, UK.
    Thekilakkattil, Abhilash
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Gettings, Oliver
    University of York, York, UK.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Chen, Jian-Jia
    Technische Universität, Dortmund, Germany..
    Exact Speedup Factors and Sub-Optimality for Non-Preemptive Scheduling2018Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, s. 208-246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fixed priority scheduling is used in many real-time systems; however, both preemptive and non-preemptive variants (FP-P and FP-NP) are known to be sub-optimal when compared to an optimal uniprocessor scheduling algorithm such as preemptive Earliest Deadline First (EDF-P). In this paper, we investigate the sub-optimality of xed priority non-preemptive scheduling. Speci cally, we derive the exact processor speed-up factor required to guarantee the feasibility under FP-NP (i.e. schedulablability assuming an optimal priority assignment) of any task set that is feasible under EDF-P. As a consequence of this work, we also derive a lower bound on the sub-optimality of non-preemptive EDF (EDF-NP). As this lower bound matches a recently published upper bound for the same quantity, it closes the exact sub-optimality for EDF-NP. It is known that neither preemptive, nor non-preemptive xed priority scheduling dominates the other, in other words, there are task sets that are feasible on a processor of unit speed under FP-P that are not feasible under FP-NP and vice-versa. Hence comparing these two algorithms, there are non-trivial speedup factors in both directions. We derive the exact speed-up factor required to guarantee the FP-NP feasibility of any FP-P feasible task set. Further, we derive the exact speed-up factor required to guarantee FP-P feasibility of any constrained-deadline FP-NP feasible task set.

  • 7.
    Gustafsson, Jan
    et al.
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Lisper, Björn
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Kirner, Raimund
    Technische Universität Wien, Austria.
    Puschner, Peter
    Technische Universität Wien, Austria.
    Code Analysis for Temporal Predictability2006Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 32, nr 3, s. 253-277Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The execution time of software for hard real-time systems must be predictable. Further, safe and not overly pessimistic bounds for the worst-case execution time (WCET) must be computable. We conceived a programming strategy called WCET-oriented programming and a code transformation strategy, the single-path conversion, that aid programmers in producing code that meets these requirements. These strategies avoid and eliminate input-data dependencies in the code. The paper describes the formal analysis, based on abstract interpretation, that identifies input-data dependencies in the code and thus forms the basis for the strategies provided for hard real-time code development.

  • 8.
    Isovic, Damir
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Fohler, Gerhard
    Handling Mixed Task Sets in Combined Offline and Online Scheduled Real-Time Systems2009Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 43, nr 3, s. 296-325Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many industrial applications with real-time demands are composed of mixed sets of tasks with a variety of requirements. These can be in the form of standard timing constraints, such as period and deadline, or complex, e.g., to express application specific or non temporal constraints, reliability, performance, etc. Arrival patterns determine whether tasks will be treated as periodic, sporadic, or aperiodic. As many algorithms focus on specific sets of task types and constraints only, system design has to focus on those supported by a particular algorithm, at the expense of the rest. In this paper, we present a method to deal with a combination of mixed sets of tasks and constraints: periodic tasks with complex and simple constraints, soft and firm aperiodic, and in particular sporadic tasks. We propose the use of an offline scheduler to manage complex timing and resource constraints of periodic tasks and transform these into a simple EDF model with start-times and deadlines. On top of the offline schedule, sporadic tasks are guaranteed based on their worst-case activation frequencies. Then at run-time, an extension to EDF ensures feasible execution of tasks with complex constraints in the presence of additional tasks or overloads. It allows changes in the offline generated schedule to insert soft and firm aperiodic tasks by shifting the execution of offline scheduled tasks within their feasibility windows. Furthermore, the online algorithm uses the exact knowledge about sporadic arrivals to reduce the pessimism introduced by worst-case assumption, i.e., the resources unused by sporadic tasks are reclaimed to improve response times and acceptance of firm aperiodic tasks. A simulation study underlines the effectiveness of the proposed approach.

  • 9.
    J. Bril, Reinder
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. Tech Univ Eindhoven, Eindhoven, Netherlands.
    Altmeyer, Sebastian
    Univ Amsterdam, Amsterdam, Netherlands.
    van den Heuvel, Martijn M. H. P.
    Tech Univ Eindhoven, Eindhoven, Netherlands.
    Davis, Robert I.
    Univ York, York, N Yorkshire, England.
    Behnam, Moris
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Fixed priority scheduling with pre-emption thresholds and cache-related pre-emption delays: integrated analysis and evaluation2017Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 53, nr 4, s. 403-466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Commercial off-the-shelf programmable platforms for real-time systems typically contain a cache to bridge the gap between the processor speed and main memory speed. Because cache-related pre-emption delays (CRPD) can have a significant influence on the computation times of tasks, CRPD have been integrated in the response time analysis for fixed-priority pre-emptive scheduling (FPPS). This paper presents CRPD aware response-time analysis of sporadic tasks with arbitrary deadlines for fixed-priority pre-emption threshold scheduling (FPTS), generalizing earlier work. The analysis is complemented by an optimal (pre-emption) threshold assignment algorithm, assuming the priorities of tasks are given. We further improve upon these results by presenting an algorithm that searches for a layout of tasks in memory that makes a task set schedulable. The paper includes an extensive comparative evaluation of the schedulability ratios of FPPS and FPTS, taking CRPD into account. The practical relevance of our work stems from FPTS support in AUTOSAR, a standardized development model for the automotive industry. [(This paper forms an extended version of Bril et al. (in Proceedings of 35th IEEE real-time systems symposium (RTSS), 2014). The main extensions are described in Sect. 1.2.].

  • 10.
    Liu, Meng
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Becker, Matthias
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Behnam, Moris
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Using Non-Preemptive Regions and Path Modification to Improve Schedulability of Real-Time Traffic over Priority-Based NoCs2017Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, nr 6, s. 886-915Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Network-on-Chip (NoC) is a preferred communication medium for massively parallel platforms. Fixed-priority based scheduling using virtual-channels is one of the promising solutions to support real-time traffic in on-chip networks. Most of the existing works regarding priority-based NoCs use a flit-level preemptive scheduling. Under such a mechanism, preemptions can only happen between the transmissions of successive flits but not during the transmission of a single flit. In this paper, we present a modified framework where the non-preemptive region of each NoC packet increases from a single flit. Using the proposed approach, the response times of certain traffic flows can be reduced, which can thus improve the schedulability of the whole network. As a result, the utilization of NoCs can be improved by admitting more real-time traffic. Schedulability tests regarding the proposed framework are presented along with the proof of the correctness. Additionally, we also propose a path modification approach on top of the non-preemptive region based method to further improve schedulability. A number of experiments have been performed to evaluate the proposed solutions, where we can observe significant improvement on schedulability compared to the original flit-level preemptive NoCs. 

  • 11.
    Mäki-Turja, Jukka
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Nolin, Mikael
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Efficient implementation of tight response-times for tasks with offsets2008Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 40, nr 1, s. 77-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier approximate response time analysis (RTA) methods for tasks with offsets (transactional task model) exhibit two major deficiencies: (i) They overestimate the calculated response times resulting in an overly pessimistic result. (ii) They suffer from time complexity problems resulting in an RTA method that may not be applicable in practice. This paper shows how these two problems can be alleviated and combined in one single fast-and-tight RTA method that combines the best of worlds, high precision response times and a fast approximate RTA method. Simulation studies, on randomly generated task sets, show that the response time improvement is significant, typically about 15% tighter response times in 50% of the cases, resulting in about 12% higher admission probability for low priority tasks subjected to admission control.

    Simulation studies also show that speedups of more than two orders of magnitude, for realistically sized tasks sets, compared to earlier RTA analysis techniques, can be obtained.

    Other improvements such as Palencia Gutierrez, Gonzalez Harbour (Proceedings of the 20th IEEE real-time systems symposium (RTSS), pp. 328-339, 1999), Redell (Technical Report TRITA-MMK 2003:4, Dept. of Machine Design, KTH, 2003) are orthogonal and complementary which means that our method can easily be incorporated also in those methods. Hence, we conclude that the fast-and-tight RTA method presented is the preferred analysis technique when tight response-time estimates are needed, and that we do not need to sacrifice precision for analysis speed; both are obtained with one single method. 

  • 12.
    Nemati, Farhang
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Resource Sharing among Real-Time Components under Multiprocessor Clustered Scheduling2013Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 49, nr 5, s. 580-613Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we propose a general synchronization protocol for resource sharing among independently-developed real-time applications (components) on multi-core platforms. This protocol is a generalization of a previously proposed synchronization protocol (MSOS). In our proposed protocol, each component is statically allocated on a dedicated subset of processors (called cluster). A component has its own internal scheduler by which its tasks are scheduled. In this paper we focus on multiprocessor global fixed-priority preemptive scheduling algorithms to be used to schedule the tasks inside each component. Sharing the local resources is handled by the Priority Inheritance Protocol (PIP). For sharing the global resources (inter-component resource sharing) we have studied usage of FIFO and Round-Robin queues for access the resources across the components and usage of FIFO and prioritized queues inside the components. We have derived schedulability analysis for the different queue handling alternatives and compared their performance by using experimental evaluations. Finally, we have shown that the integration phase can be formulated in the form of a nonlinear integer programming problem where solution techniques in this domain can be used to minimize the total number of processors required to guarantee the schedulability of all components. As a proof of concept we have only provided the formulation for FIFO queues.

  • 13.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    The Limited-preemptive Feasibility of Real-time Tasks on Uniprocessors2015Inngår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 51, nr 3, s. 247-273Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The preemptive scheduling paradigm is known to strictly dominate the non-preemptive scheduling paradigm with respect to feasibility. On the other hand, preemptively scheduling real-time tasks on uniprocessors, unlike non-preemptive scheduling, may lead to unschedulability due to, e.g., preemption related overheads. The limited-preemptive scheduling paradigm, which is a generalization of preemptive and non-preemptive paradigms, has, however, the potential to reduce the preemption related overheads while enabling high processor utilization. In this paper, we focus on the characterization of the effects of increasing the computational resources on the limited-preemptive feasibility of real-time tasks in order to quantify the sub-optimality of limited-preemptive scheduling. Specifically, we first derive the required processor speed-up bound that guarantees limited-preemptive feasibility of any uniprocessor feasible taskset. Secondly, we demonstrate the applicability of the results in the context of controlling preemption related overheads while minimizing the required processor speed-up. In particular, we identify the preemptive behavior that minimizes preemption-related overheads, as well as derive the optimal processor speed associated with it. Finally, we examine the consequences of having more processors on limited-preemptive feasibility and derive the bound on the number of processors that guarantees a specified limited-preemptive behavior for any uniprocessor feasible real-time taskset. This paper essentially bridges the preemptive and non-preemptive real-time scheduling paradigms by providing significant theoretical results building on the limitedpreemptive scheduling paradigm, as well as provides analytical inputs to developers in order to perform various trade-offs, e.g., code refactoring, to control the preemptive behavior of real-time tasks.

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