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1.
  • Yin, Hang, 1982- (författare)
  • Introducing Mode Switch in Component-Based Software Development
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Self-adaptivity, characterized by the ability to dynamically adjust behavior at runtime, is a growing trend in the evolution of modern embedded systems. While self-adaptive systems tend to be flexible and autonomous, self-adaptivity may inevitably complicate software design, test and analysis. A strategy for taming the growing software complexity of self-adaptive systems is to partition system behaviors into different operational modes specified at design time. Such a multi-mode system can change behavior by switching between modes at runtime under certain circumstances. Multi-mode systems can benefit from a complementary approach to the software development of complex systems: Component-Based Software Engineering (CBSE), which fosters reuse of independently developed software components. However, the state-of-the-art component-based development of multi-mode systems does not take full advantage of CBSE, as reuse of modes at component level is barely addressed. Modes are often treated as system properties, while mode switches are handled by a global mode manager. This centralized mode management entails global information of all components, whereas the global information may be inaccessible in component-based systems. Another potential problem is that a single mode manager does not scale well, particularly at design time,  for a large number of components and modes. In this thesis we propose a distributed solution to the component-based development of multi-mode systems, aiming for a more efficient and scalable mode management. Our goal is to fully incorporate modes in software component reuse, supporting reuse of multi-mode components, i.e., components able to run in multiple modes. We have developed a generic framework, the Mode-Switch Logic (MSL), which not only supports reuse of multi-mode components but also provides runtime mechanisms for handling mode switch. MSL includes three fundamental elements: (1) a mode-aware component model with the formal specification of reusable multi-mode software components; (2) a mode mapping mechanism for the seamless composition of multi-mode components; and (3) a mode-switch runtime mechanism which is executed by each component in isolation from its functional execution and coordinates the mode switches of different components without the need of global mode information. The mode-switch runtime mechanism has been verified by model checking in conjunction with mathematical proofs. We also provide a mode-switch timing analysis for the runtime mechanism to respect real-time requirements. MSL is dedicated to the mode aspect of a system irrespective of component execution semantics, thus independent of the choice of component models. We have integrated MSL in the ProCom component model with the extension of support for reuse of multi-mode components and distributed mode-switch handling. Although the distributed mode-switch handling of MSL is more flexible and scalable than the conventional centralized approach, when components are deployed on a single hardware platform and global mode information is available, centralized mode-switch handling is more efficient in terms of runtime overhead and mode-switch time. Hence, MSL is supplemented with a mode transformation technique to enhance runtime mode-switch efficiency by converting the distributed mechanism to a centralized mechanism. MSL together with the mode transformation technique has been implemented in a prototype tool where one can build multi-mode systems by reusing multi-mode components. The applicability of MSL is demonstrated in two proof-of-concept case studies.
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2.
  • Afshar, Sara (författare)
  • Lock-Based Resource Sharing for Real-Time Multiprocessors
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Embedded systems are widely used in the industry and are typically resource constrained, i.e., resources such as processors, I/O devices, shared buffers or shared memory might be limited in the system. Hence, techniques that can enable an efficient usage of processor bandwidths in such systems are of great importance. Locked-based resource sharing protocols are proposed as a solution to overcome resource limitation by allowing the available resources in the system to be safely shared. In recent years, due to a dramatic enhancement in the functionality of systems, a shift from single-core processors to multi-core processors has become inevitable from an industrial perspective to tackle the raised challenges due to increased system complexity. However, the resource sharing protocols are not fully mature for multi-core processors. The two classical multi-core processor resource sharing protocols, spin-based and suspension-based protocols, although providing mutually exclusive access to resources, can introduce long blocking delays to tasks, which may be unacceptable for many industrial applications. In this thesis we enhance the performance of resource sharing protocols for partitioned scheduling, which is the de-facto scheduling standard for industrial real-time multi-core processor systems such as in AUTOSAR, in terms of timing and memory requirements. A new scheduling approach uses a resource efficient hybrid approach combining both partitioned and global scheduling where the partitioned scheduling is used to schedule the major number of tasks in the system. In such a scheduling approach applications with critical task sets use partitioned scheduling to achieve higher level of predictability. Then the unused bandwidth on each core that is remained from partitioning is used to schedule less critical task sets using global scheduling to achieve higher system utilization. These scheduling schema however lacks a proper resource sharing protocol since the existing protocols designed for partitioned and global scheduling cannot be directly applied due to the complex hybrid structure of these scheduling frameworks. In this thesis we propose a resource sharing solution for such a complex structure. Further, we provide the blocking bounds incurred to tasks under the proposed protocols and enhance the schedulability analysis, which is an essential requirement for real-time systems, with the provided blocking bounds.
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3.
  • Becker, Matthias, 1986- (författare)
  • Efficient Resource Management for Many-Core based Industrial Real-Time Systems
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The increased complexity of today’s industrial embedded systems stands inneed for more computational power while most systems must adhere to a restrictedenergy consumption, either to prolong the battery lifetime or to reduceoperational costs. The many-core processor is therefore a natural fit. Due tothe simple architecture of the compute cores, and therefore their good analyzability,such processors are additionally well suited for real-time applications.In our research, we focus on two particular problems which need to be addressedin order to pave the way into the many-core era. The first area is powerand thermal aware execution frameworks, where we present different energyaware extensions to well known load balancing algorithms, allowing them todynamically scale the number of active cores depending on their workload.In contrast, an additional framework is presented which balances workloadsto minimize temperature gradients on the die. The second line of works focuseson industrial standards in the face of massively parallel platforms, wherewe address the automotive and automation domain. We present an executionframework for IEC 61131-3 applications, allowing the consolidation of severalIEC 61131-3 applications on the same platform. Additionally, we discussseveral architectural options for the AUTOSAR software architecture on suchmassively parallel platforms.
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4.
  • Bujosa Mateu, Daniel (författare)
  • Enhancing TSN Adoption by Industry : Tools to Support Migrating Ethernet-based Legacy Networks into TSN
  • 2023
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • New technologies present opportunities and challenges for industries. One major challenge is the ease, or even feasibility, of its adoption. The Time-Sensitive Networking (TSN) standards offer a range of features relevant to various applications and are key for the transition to Industry 4.0. These features include deterministic zero-jitter, low-latency data transmission, transmission of traffic with various levels of time-criticality on the same network, fault tolerance mechanisms, and advanced network management allowing dynamic reconfiguration.This thesis aims to develop tools that enable the industry to adopt TSN easily and efficiently. Specifically, we create tools that facilitate the migration of legacy networks to TSN, enabling the preservation of most of the legacy systems and solutions while reducing costs and adoption time. Firstly, we introduce LETRA (Legacy Ethernet-based Traffic Mapping Tool), a tool for mapping Ethernet-based legacy traffic to the new TSN traffic classes. Secondly, we develop HERMES (Heuristic Multi-queue Scheduler), a heuristic Time-Triggered (TT) traffic scheduler that can meet the characteristics of legacy systems and provide quick results suitable for reconfiguration. Thirdly, we develop TALESS (TSN with Legacy End-Stations Synchronization), a mechanism to avoid adverse consequences caused by the lack of synchronization between legacy systems and TSN-based ones, as not all legacy systems need to support the TSN synchronization mechanisms. Finally, we improve Stream Reservation Protocol (SRP) to enhance Audio-Video Bridging (AVB) traffic configuration in terms of termination and consistency.
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5.
  • Johansson, Bjarne, 1977- (författare)
  • Dependable Distributed Control System : Redundancy and Concurrency defects
  • 2022
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Intelligent devices, interconnectivity, and information exchange are characteristics often associated with Industry 4.0. A peer-to-peer-oriented architecture with the network as the system center succeeds the traditional controller-centric topology used in today's distributed control systems, improving information exchange in future designs. The network-centric architecture allows IT-solution such as cloud, fog, and edge computing to enter the automation industry. IT-solution that rely on virtualization techniques such as virtual machines and containers. Virtualization technology, combined with virtual instance management, provide the famous elasticity that cloud computing offer. Container management systems like Kubernetes can scale the number of containers to match the service demand and redeploy containers affected by failures.Distributed control systems constitute automation infrastructure core in many critical applications and domains. The criticality puts high dependability requirements upon the systems, i.e., dependability is essential. High-quality software and redundancy solutions are examples of traditional ways to increase dependability. Dependability is the common denominator for the challenges addressed in this thesis. Challenges that range from concurrency defect localization with static code analysis to utilization of failure recovery mechanisms provided by container management systems in a control system context.We evaluate the feasibility of locating concurrency defects in embedded industrial software with static code analysis. Furthermore, we propose a deployment agnostic failure detection and role selection mechanism for controller redundancy in a network-centric context. Finally, we use the container management system Kubernetes to orchestrate a cluster of virtualized controllers. We evaluate the failure recovery properties of the container management system in combination with redundant virtualized controllers - redundant controllers using the proposed failure detection and role selection solution.
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6.
  • Lu, Yue (författare)
  • Pragmatic Approaches for Timing Analysis of Real-Time Embedded Systems
  • 2012
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Many industrial real-time embedded systems are very large, flexible and highly configurable software systems. Such systems are becoming ever more complex, and we are reaching the stage in which even if existing timing analysis was feasible from a cost and technical perspective, the analysis results are overly pessimistic, making them less useful to practitioners. When combined with the fact that most existing real-time embedded systems tend to be probabilistic in nature due to high complexity featured by advanced hardware and more flexible and/or adaptive software applications, this advocates moving toward pragmatic timing analysis, which is not specifically limited by constrains related to intricate task execution and temporal dependencies in systems. In this thesis, we address this challenge, and we present two pragmatic timing analysis techniques for real-time embedded systems.The first contribution is a simulation-based analysis using two simple yet novel search algorithms of meta-heuristic type, i.e., a form of genetic algorithms and hill-climbing with random restarts, yielding substantially better results, comparing traditional Monte Carlo simulation-based analysis methods.As the second contribution, we discuss one major issue when using simulation-based methods for timing analysis of real-time embedded systems, i.e., model validity, which determines whether a simulation model is an accurate representation of the target system at the certain level of satisfaction, from a task response time and execution time perspective.The third contribution is a statistical timing analysis, which, unlike the traditional timing analysis, does not require worst-case execution times of tasks as inputs, and computes a probabilistic task worst-case response time estimate pertaining to a configurable task reliability requirement.In addition, a number of tools have been implemented and used for the evaluation of our research results. Our evaluations, using different simulation models depicting fictive but representative industrial control applications, have shown a clear indication that our new timing analysis techniques have the potential to be both applicable and useful in practice, as well as being complementary to software testing focusing on timing properties of real-time embedded systems that are used in various domains of industrial automation, aerospace and defense, automotive telematics, etc.
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7.
  • Nemati, Farhang, Senior Lecturer, 1975- (författare)
  • Partitioned Scheduling of Real-Time Tasks on Multi-core Platforms
  • 2010
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In recent years multiprocessor architectures have become mainstream, and multi-core processors are found in products ranging from small portable cell phones to large computer servers. In parallel, research on real-time systems has mainly focused on traditional single-core processors. Hence, in order for real-time systems to fully leverage on the extra capacity offered by new multi-core processors, new design techniques, scheduling approaches, and real-time analysis methods have to be developed.In the multi-core and multiprocessor domain there are mainly two scheduling approaches, global and partitioned scheduling. Under global scheduling each task can execute on any processor at any time while under partitioned scheduling tasks are statically allocated to processors and migration of tasks among processors is not allowed. Besides simplicity and efficiency of partitioned scheduling protocols, existing scheduling and synchronization methods developed for single-core processor platforms can more easily be extended to partitioned scheduling. This also simplifies migration of existing systems to multi-cores. An important issue related to partitioned scheduling is distribution of tasks among processors which is a bin-packing problem.In this thesis we propose a partitioning framework for distributing tasks on the processors of multi-core platforms. Depending on the type of performance we desire to achieve, the framework may distribute a task set differently, e.g., in an application in which tasks process huge amounts of data the goal of the framework may be to decrease cache misses.Furthermore, we propose a blocking-aware partitioning heuristic algorithm to distribute tasks onto the processors of a multi-core architecture. The objective of the proposed algorithm is to decrease blocking overhead of tasks which reduces the total utilization and has the potential to reduce the number of required processors.Finally, we have implemented a tool to facilitate evaluation and comparison of different multiprocessor scheduling and synchronization approaches, as well as different partitioning heuristics. We have applied the tool in the evaluation of several partitioning heuristic algorithms, and the tool is flexible to which any new scheduling or synchronization protocol as well as any new partitioning heuristic can easily be added.
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8.
  • Afshar, Sara (författare)
  • Lock-Based Resource Sharing in Real-Time Multiprocessor Platforms
  • 2014
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Embedded systems are typically resource constrained, i.e., resources such as processors, I/O devices, shared buffers or shared memory can be limited for tasks in the system. Therefore, techniques that enable an efficient usage of such resources are of great importance.In the industry, typically large and complex software systems are divided into smaller parts (applications) where each part is developed independently. Migration towards multiprocessor platforms has become inevitable from an industrial perspective. Due to such migration and to efficient use of system resources, these applications eventually may be integrated on a shared multiprocessor platform. In order to facilitate the integration phase of the applications on a shared platform, the timing and resource requirements of each application can be provided in an interface when the application is developed. The system integrator can benefit from such provided information in the interface of each application to ease the integration process. In this thesis, we have provided the resource and timing requirements of each application in their interfaces for applications that may need several processors to be allocated on when they are developed.Although many scheduling techniques have been studied for multiprocessor systems, these techniques are usually based on the assumption that tasks are independent, i.e. do not share resources other than the processors. This assumption is typically not true. In this thesis, we provide an extension to such systems to handle sharing of resources other than processor among tasks. Two traditional approaches exist for multiprocessor systems to schedule tasks on processors. A recent scheduling approach for multiprocessors has combined the two traditional approaches and achieved a hybrid more efficient approach compared to the two previous one. Due to the complex nature of this scheduling approach the conventional approaches for resource sharing could not be used straight forwardly. In this thesis, we have modified resource sharing approaches such that they can be used in such hybrid scheduling systems. A second concern is that enabling resource sharing in the systems can cause unpredictable delays and variations in response time of tasks which can degrade system performance. Therefore, it is of great significance to improve the resource handling techniques to reduce the effect of imposed delays caused by resource sharing in a multiprocessor platform. In this thesis we have proposed alternative techniques for resource handling that can improve system performance for special setups.
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9.
  • Ashjaei, Mohammad, 1980- (författare)
  • Multi-Hop Real-Time Communication over Switched Ethernet Technology
  • 2014
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Switched Ethernet technology has been introduced to be exploited in real-time communication systems due to its features such as its high throughput and wide availability, hence being a cost-effective solution. Many real-time switched Ethernet protocols have been developed, preserving the profits of traditional Ethernet technology, to overcome the limitations imposed by using commercially available (COTS) switches. These limitations mainly originate from the non-deterministic behavior of the Ethernet switches inherent in the use of FIFO queues and a limited number of priority levels. In our research we focus on two particular real-time communication technologies, one based on COTS Ethernet switches named the FTT-SE architecture and the other using a modified Ethernet switch called the HaRTES architecture. Both architectures are based on a master-slave technique supporting different and temporally isolated traffic types including real-time periodic, real-time sporadic and non-real-time traffic. Also, they provide mechanisms implementing adaptivity as a response to the requirements imposed by dynamic real-time applications. Nevertheless, the two mentioned architectures were originally developed for a simple network consisting of a single switch, and they were lacking support for multi-hop communication. In industrial applications, multi-hop communication is essential as the networks comprise a high number of nodes, that is far beyond the capability of a single switch. In this thesis, we study the challenges of building multi-hop communication using the FTT-SE and the HaRTES architectures. We propose different architectures to provide multi-hop communication while preserving the key characteristics of the single-switch architecture such as timeliness guarantee, resource efficiency, adaptivity and dynamicity. We develop a response time analysis for each proposed architecture and we compare them to assess their corresponding benefits and limitations. Further, we develop a simulation tool to evaluate the solutions.
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10.
  • Ashjaei, Mohammad, 1980- (författare)
  • Real-Time Communication over Switched Ethernet with Resource Reservation
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Due to the need for advanced computer-controlled functionality in distributed embedded systems the requirements on network communication are becoming overly intricate. This dissertation targets the requirements that are concerned with real-time guarantees, run-time adaptation, resource utilization and flexibility during the development. The Flexible Time-Triggered Switched Ethernet (FTT-SE) and Hard Real-Time Ethernet Switching (HaRTES) network architectures have emerged as two promising solutions that can cater for these requirements. However, these architectures do not support multi-hop communication as they are originally developed for single-switch networks. This dissertation presents a fundamental contribution in multi-hop real-time communication over the FTT-SE and HaRTES architectures targeting the above mentioned requirements. It proposes and evaluates various solutions for scheduling and forwarding the traffic through multiple switches in these architectures. These solutions preserve the ability of dynamic adaptation without jeopardizing real-time properties of the architectures. Moreover, the dissertation presents schedulability analyses for the timeliness verification and evaluation of the proposed solutions as well as several protocols to support run-time adaptation in the multi-hop communication. Finally, the work led to an end-to-end resource reservation framework, based on the proposed multi-hop architectures, to support flexibility during the development of the systems. The efficiency of the proposed solutions is evaluated on various case studies that are inspired from industrial systems.
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11.
  • Lu, Yue (författare)
  • Approximation Techniques for Timing Analysis of Complex Real-Time Embedded Systems
  • 2010
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • To date, many industrial embedded systems are very large, flexible, and highly configurable software systems, containing millions of lines of code and consisting of hundreds of tasks, many with real-time constraints, being triggered in complex, nested patterns. Furthermore, the temporal dependencies between tasks in such systems are difficult to determine analytically, and they vary the execution time and response time of tasks greatly. We refer to such systems as Complex Real-Time Embedded Systems (CRTES). To maintain, analyze and reuse such CRTES is very difficult and expensive, which, nevertheless, offers high business value in response to great concern in industry. Moreover, in such context, not only the functional behavior of systems has to be assured, but also non-functional properties such as the temporal behavior, i.e., Worst-Case Response Time (WCRT) of the adhering tasks in systems has to be known. However, due to high complexity of such systems and the nature of the problem, the exact WCRT of tasks is impossible to find in practice, but may only be bounded. In addition, the existing relatively well-developed theories for modeling and analysis of real-time systems are having problems, which limit their application in the context. In this thesis, we address this challenge, and present a framework for approximate timing analysis of CRTES that provides a tight interval of WCRT estimates of tasks by the usage of three novel contributions. The first contribution is a novel statistical approach to WCRT analysis of CRTES. The proposed algorithm combines Extreme Value Theory (EVT) with other statistical methods in order to produce a probabilistic WCRT estimate, using response time data from either Monte Carlo simulations of a detailed model of the system, or time-stamped traces of the real system execution. The focus of the method is to give a WCRT prediction with a given probability of being exceeded, which potentially could be considered as an upper bound on the WCRT estimate in systems, especially in the case where conventional timing analysis methods cannot be applied. The second contribution is to introduce a concrete process of formally obtaining the exact value of both Worst-Case Execution Time (WCET) and WCRT of tasks in the system model by using upper-part binary search algorithms together with a timed model checker, after a semantic-preserving model transformation. The underline premise is that the size and complexity of CRTES have to be reduced such that they can be manageable by the model checking tool. The third contribution is to apply an optimization algorithm, in this case a meta-heuristic search algorithm, on top of the traditional Monte Carlo simula-tion, which yields substantially better results with respect to tight lower bounds on WCRT estimates of tasks in CRTES. In addition, a number of tools have been implemented and used for the evaluation of the research results. These evaluations, using four simulation models depicting two fictive but representative industrial control applications, give clear indication that the proposed methods have the potential to be both applicable and useful in practice.
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12.
  • Nemati, Farhang (författare)
  • Resource Sharing in Real-Time Systems on Multiprocessors
  • 2012
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In recent years multiprocessor architectures have become mainstream, and multi-core processors are found in products ranging from small portable cell phones to large computer servers. In parallel, research on real-time systems has mainly focused on traditional single-core processors. Hence, in order for real-time systems to fully leverage on the extra capacity offered by new multi-core processors, new design techniques, scheduling approaches, and real-time analysis methods have to be developed. In the multi-core and multiprocessor domain there are mainly two scheduling approaches, global and partitioned scheduling. Under global scheduling each task can execute on any processor at any time while under partitioned scheduling tasks are statically allocated to processors and migration of tasks among processors is not allowed. Besides simplicity and efficiency of partitioned scheduling protocols, existing scheduling and synchronization techniques developed for single-core processor platforms can more easily be extended to partitioned scheduling. This also simplifies migration of existing systems to multi-cores. An important issue related to partitioned scheduling is the distribution of tasks among the processors, which is a bin-packing problem. In this thesis we propose a blocking-aware partitioning heuristic algorithm to distribute tasks onto the processors of a multi-core architecture. The objective of the proposed algorithm is to decrease the blocking overhead of tasks, which reduces the total utilization and has the potential to reduce the number of required processors. In industrial embedded software systems, large and complex systems are usually divided into several components (applications) each of which is developed independently without knowledge of each other, and potentially in parallel. However, the applications may share mutually exclusive resources when they co-execute on a multi-core platform which introduce a challenge for the techniques needed to ensure predictability. In this thesis we have proposed a new synchronization protocol for handling mutually exclusive resources shared among real-time applications on a multi-core platform. The schedulability analysis of each application is performed in isolation and parallel and the requirements of each application with respect to the resources it may share are included in an interface. The protocol did not originally consider any priorities among the applications. We have proposed an additional version of the protocol which grants access to resources based on priorities assigned to the applications. We have also proposed an optimal priority assignment algorithm to assign unique priorities to the applications sharing resources. Our evaluations confirm that the protocol together with the priority assignment algorithm outperforms existing alternatives in most cases. In the proposed synchronization protocol each application is assumed to be allocated on one dedicated core. However, in this thesis we have further extended the synchronization protocol to be applicable for applications allocated on multiple dedicated cores of a multi-core platform. Furthermore, we have shown how to efficiently calculate the resource hold times of resources for applications. The resource hold time of a resource for an application is the maximum duration of time that the application may lock the resource whenever it requests the resource. Finally, the thesis discusses and proposes directions for future work.
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13.
  • Rosén, Jakob, 1977- (författare)
  • Predictable Real-Time Applications on Multiprocessor Systems-on-Chip
  • 2011
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Being predictable with respect to time is, by definition, a fundamental requirement for any real-time system. Modern multiprocessor systems impose a challenge in this context, due to resource sharing conflicts causing memory transfers to become unpredictable. In this thesis, we present a framework for achieving predictability for real-time applications running on multiprocessor system-on-chip platforms. Using a TDMA bus, worst-case execution time analysis and scheduling are done simultaneously. Since the worst-case execution times are directly dependent on the bus schedule, bus access design is of special importance. Therefore, we provide an efficient algorithm for generating bus schedules, resulting in a minimized worst-case global delay.We also present a new approach considering the average-case execution time in a predictable context. Optimization techniques for improving the average-case execution time of tasks, for which predictability with respect to time is not required, have been investigated for a long time in many different contexts. However, this has traditionally been done without paying attention to the worst-case execution time. For predictable real-time applications, on the other hand, the focus has been solely on worst-case execution time optimization, ignoring how this affects the execution time in the average case. In this thesis, we show that having a good average-case global delay can be important also for real-time applications, for which predictability is required. Furthermore, for real-time applications running on multiprocessor systems-on-chip, we present a technique for optimizing for the average case and the worst case simultaneously, allowing for a good average case execution time while still keeping the worst case as small as possible. The proposed solutions in this thesis have been validated by extensive experiments. The results demonstrate the efficiency and importance of the presented techniques.
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14.
  • Al-Dulaimy, Auday, et al. (författare)
  • Fault Tolerance in Cloud Manufacturing : An Overview
  • 2023
  • Ingår i: Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST. - : Springer Science and Business Media Deutschland GmbH. - 9783031318900 ; , s. 89-101
  • Konferensbidrag (refereegranskat)abstract
    • Utilizing edge and cloud computing to empower the profitability of manufacturing is drastically increasing in modern industries. As a result of that, several challenges have raised over the years that essentially require urgent attention. Among these, coping with different faults in edge and cloud computing and recovering from permanent and temporary faults became prominent issues to be solved. In this paper, we focus on the challenges of applying fault tolerance techniques on edge and cloud computing in the context of manufacturing and we investigate the current state of the proposed approaches by categorizing them into several groups. Moreover, we identify critical gaps in the research domain as open research directions. © 2023, ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering.
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15.
  • Alhashimi, Anas, et al. (författare)
  • Change-Point and Model Estimation with Heteroskedastic Noise and Unknown Model Structure
  • 2023
  • Ingår i: Int. Conf. Control, Decis. Inf. Technol., CoDIT. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350311402 ; , s. 2126-2132
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we investigate the problem of modeling time-series as a process generated through (i) switching between several independent sub-models; (ii) where each sub-model has heteroskedastic noise, and (iii) a polynomial bias, describing nonlinear dependency on system input. First, we propose a generic nonlinear and heteroskedastic statistical model for the process. Then, we design Maximum Likelihood (ML) parameters estimation method capable of handling heteroscedasticity and exploiting constraints on model structure. We investigate solving the intractable ML optimization using population-based stochastic numerical methods. We then find possible model change-points that maximize the likelihood without over-fitting measurement noise. Finally, we verify the usefulness of the proposed technique in a practically relevant case study, the execution-time of odometry estimation for a robot operating radar sensor, and evaluate the different proposed procedures using both simulations and field data.
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16.
  • Becker, Matthias, 1986- (författare)
  • Consolidating Automotive Real-Time Applications on Many-Core Platforms
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Automotive systems have transitioned from basic transportation utilities to sophisticated systems. The rapid increase in functionality comes along with a steep increase in software complexity. This manifests itself in a surge of the number of functionalities as well as the complexity of existing functions. To cope with this transition, current trends shift away from today’s distributed architectures towards integrated architectures, where previously distributed functionality is consolidated on fewer, more powerful, computers. This can ease the integration process, reduce the hardware complexity, and ultimately save costs.One promising hardware platform for these powerful embedded computers is the many-core processor. A many-core processor hosts a vast number of compute cores, that are partitioned on tiles which are connected by a Network-on-Chip. These natural partitions can provide exclusive execution spaces for different applications, since most resources are not shared among them. Hence, natural building blocks towards temporally and spatially separated execution spaces exist as a result of the hardware architecture.Additionally to the traditional task local deadlines, automotive applications are often subject to timing constraints on the data propagation through a chain of semantically related tasks. Such requirements pose challenges to the system designer as they are only able to verify them after the system synthesis (i.e. very late in the design process).In this thesis, we present methods that transform complex timing constraints on the data propagation delay to precedence constraints between individual jobs. An execution framework for the cluster of the many-core is proposed that allows access to cluster external memory while it avoids contention on shared resources by design. A partitioning and configuration of the Network-on-Chip provides isolation between the different applications and reduces the access time from the clusters to external memory. Moreover, methods that facilitate the verification of data propagation delays in each development step are provided. 
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17.
  • Behnam, Moris (författare)
  • Hierarchical Real Time Scheduling and Synchronization
  • 2008
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    •   The Hierarchical Scheduling Framework (HSF) has been introduced to enable compositional schedulability analysis and execution of embedded software systems with real-time constraints. In this thesis, we consider a system consisting of a number of semi-independent components called subsystems, and these subsystems are allowed to share logical resources. The HSF provides CPU-time to the subsystems and it guarantees that the individual subsystems respect their allocated CPU budgets. However, if subsystems are allowed to share logical resources, extra complexity with respect to analysis and run-time mechanisms is introduced. In this thesis we address three issues related to hierarchical scheduling of semi-independent subsystems. In the first part, we investigate the feasibility of implementing the hierarchical scheduling framework in a commercial operating system, and we present the detailed figures of various key properties with respect to the overhead of the implementation. In the second part, we studied the problem of supporting shared resources in a hierarchical scheduling framework and we propose two different solutions to support resource sharing. The first proposed solution is called SIRAP, a synchronization protocol for resource sharing in hierarchically scheduled open real-time systems, and the second solution is an enhanced overrun mechanism. In the third part, we present a resource efficient approach to minimize system load (i.e., the collective CPU requirements to guarantee the schedulability of hierarchically scheduled subsystems). Our work is motivated from a tradeoff between reducing resource locking times and reducing system load. We formulate an optimization problem that determines the resource locking times of each individual subsystem with the goal of minimizing the system load subject to system schedulability. We present linear complexity algorithms to find an optimal solution to the problem, and we prove their correctness              
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18.
  • Behnam, Moris, 1973- (författare)
  • Synchronization Protocols for a Compositional Real-Time Scheduling Framework
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis we propose techniques to simplify the integration of subsystems while minimizing the overall amount of CPU resources needed to guarantee the schedulability of real-time tasks. In addition, we provide solutions to the problem of allowing for the use of logical resources requiring mutual exclusion.The contribution of the thesis is presented in three parts. In the first part, we propose a synchronization protocol, called SIRAP, to facilitate sharing of logical resources in a hierarchical scheduling framework. In addition, we extend an existing synchronization protocol, called HSRP, such that each subsystem can be developed independently. The performance of the proposed protocols is evaluated by extensive simulations. In the second part, we present an efficient schedulability analysis that exploits the lower scheduling overhead introduced by each of the proposed protocols. Finally, in the third part, we propose new methods and algorithms that find the optimal system parameters (e.g., optimal resource ceiling), that minimize the amount of CPU resources required to ensure schedulability, when using the proposed synchronization protocols in a hierarchical scheduling framework.The motivation of this work comes from an emerging industrial trend in embedded software systems development to integrate multiple applications (subsystems) on a small number of processors. The purpose of this integration is to reduce the hardware related costs as well as the communication complexity between processors. In this setting a large number of industrial applications face the problem of preserving their real-time properties after their integration onto a single processor. In addition, temporal isolation between the applications during runtime may be required to prevent failure propagation between different applications.Specifically, we propose a hierarchical scheduling framework that allows for a simplified integration of subsystems. The framework preserves the essential temporal characteristics of the subsystems, both when running in isolation as well as when they are integrated with other subsystems. In this thesis, we assume a model where a system consists of a number of subsystems. The subsystems can interact with each other using shared logical resources. The framework ensures that the individual subsystem respects its allocated share of the processor. The difficulty lies in allowing two or more subsystems to share logical resources, which introduces an additional complexity in the schedulability analysis and also increases the system load.
  •  
19.
  • Bujosa Mateu, Daniel, et al. (författare)
  • HERMES : Heuristic Multi-queue Scheduler for TSN Time-Triggered Traffic with Zero Reception Jitter Capabilities
  • 2022
  • Ingår i: ACM International Conference Proceeding Series. - New York, NY, USA : Association for Computing Machinery. - 9781450396509 ; , s. 70-80
  • Konferensbidrag (refereegranskat)abstract
    • The Time-Sensitive Networking (TSN) standards provide a toolbox of features to be utilized in various application domains.The core TSN features include deterministic zero-jitter and low-latency data transmission and transmitting traffic with various levels of time-criticality on the same network. To achieve a deterministic transmission, the TSN standards define a time-aware shaper that coordinates transmission of Time-Triggered (TT) traffic. In this paper, we tackle the challenge of scheduling the TT traffic and we propose a heuristic algorithm, called HERMES. Unlike the existing scheduling solutions, HERMES results in a significantly faster algorithm run-time and a high number of schedulable networks. HERMES can be configured in two modes of zero or relaxed reception jitter while using multiple TT queues to improve the schedulability. We compare HERMES with a constraint programming (CP)-based solution and we show that HERMES performs better than the CP-based solution if multiple TT queues are used, both with respect to algorithm run-time and schedulability of the networks.
  •  
20.
  • Bujosa Mateu, Daniel, et al. (författare)
  • Improved Clock Synchronization in TSN Networks with Legacy End-Stations
  • 2023
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • In order to enable the adoption of Time Sensitive Networking (TSN) by the industry and be more environmentally sustainable, it is necessary to develop tools to integrate legacy systems with TSN. In this paper, we propose a solution for the coexistence of different time domains from different legacy systems with their corresponding synchronization protocols in a single TSN network. To this end, we experimentally identified the effects of replacing the communications subsystem of a legacy Ethernet-based network with TSN in terms of synchronization. Based on the results, we propose a solution called TALESS (TSN with Legacy End-Stations Synchronization). TALESS is able to identify the drift between the TSN communications subsystem and the integrated legacy devices (end-stations) and modify the TSN schedule to adapt to the different time domains to avoid the effects of the lack of synchronization between them. We validate TALESS through both simulations and experiments on a prototype. Thereby we demonstrate that thanks to TALESS, legacy systems are able to synchronize through TSN and even improve features such as their reception jitter or their integrability with other legacy systems.
  •  
21.
  • Bujosa Mateu, Daniel, et al. (författare)
  • Introducing Guard Frames to Ensure Schedulability of All TSN Traffic Classes
  • 2023
  • Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
  • Konferensbidrag (refereegranskat)abstract
    • Offline scheduling of Scheduled Traffic (ST) in Time-Sensitive Networks (TSN) without taking into account the quality of service of non-ST traffic, e.g., time-sensitive traffic such as Audio-Video Bridging (AVB) traffic, can potentially cause deadline misses for non-ST traffic. In this paper, we report our ongoing work to propose a solution that, regardless of the ST scheduling algorithm being used, can ensure meeting timing requirements for non-ST traffic. To do this, we define a frame called Guard Frame (GF) that will be scheduled together with all ST frames. We show that a proper design for the GFs will leave necessary porosity in the ST schedules to ensure that all non-ST traffic will meet their timing requirements.
  •  
22.
  • Bujosa Mateu, Daniel, et al. (författare)
  • The Effects of Clock Synchronization in TSN Networks with Legacy End-Stations
  • 2022
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we present our ongoing work on proposing solutions to integrate legacy end-stations into Time-Sensitive Network (TSN) communication systems where the legacy end-stations are synchronized via their legacy clock synchronization protocol. To this end, we experimentally identify the effects of lacking synchronization or partial synchronization in TSN networks. In the experiments we show the effects of clock synchronization in different scenarios on jitter and clock drifts. Based on the experiments, we propose preliminary solutions to overcome the identified effects.
  •  
23.
  • Faragardi, Hamid Reza, 1987- (författare)
  • Optimizing Timing-Critical Cloud Resources in a Smart Factory
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis addresses the topic of resource efficiency in the context of timing critical components that are used in the realization of a Smart Factory.The concept of the smart factory is a recent paradigm to build future production systems in a way that is both smarter and more flexible. When it comes to realization of a smart factory, three principal elements play a significant role, namely Embedded Systems, Internet of Things (IoT) and Cloud Computing. In a smart factory, efficient use of computing and communication resources is a prerequisite not only to obtain a desirable performance for running industrial applications, but also to minimize the deployment cost of the system in terms of the size and number of resources that are required to run industrial applications with an acceptable level of performance. Most industrial applications that are involved in smart factories, e.g., automation and manufacturing applications, are subject to a set of strict timing constraints that must be met for the applications to operate properly. Such applications, including underlying hardware and software components that are used to run the application, constitute a real-time system. In real-time systems, the first and major concern of the system designer is to provide a solution where all timing constraints are met. To do so we need a time-predictable IoT/Cloud Computing framework to deal with the real-time constraints that are inherent in industrial applications running in a smart factory. Afterwards, with respect to the time predictable framework, the number of required computing and communication resources can and should be optimized such that the deployed system is cost efficient. In this thesis, to investigate and present solutions that provide and improve the resource efficiency of computing and communication resources in a smart factory, we conduct research following three themes: (i) multi-core embedded processors, which are the key element in terms of computing components embedded in the machinery of a smart factory, (ii) cloud computing data centers, as the supplier of a massive data storage and a large computational power, and(iii) IoT, for providing the interconnection of computing components embedded in the objects of a smart factory. Each of these themes are targeted separately to optimize resource efficiency. For each theme, we identify key challenges when it comes to achieving a resource-efficient design of the system. We then formulate the problem and propose solutions to optimize the resource efficiency of the system, while satisfying all timing constraints reflected in the model. We then propose a comprehensive resource allocation mechanism to optimize the resource efficiency in the whole system while considering the characteristics of each of these research themes. The experimental results indicate a clear improvement when it comes to timing-critical IoT / Cloud Computing resources in a smart factory. At the level of multi-core embedded devices, the total CPU usage of a quad-core processor is shown to be improved by 11.2%. At the level of Cloud Computing, the number of cloud servers that are required to execute a given set of real-time applications is shown to be reduced by 25.5%. In terms of network components that are used to collect sensor data, our proposed approach reduces the total deployment cost of thesystem by 24%. In summary these results all contribute towards the realization of a future smart factory.
  •  
24.
  • Friebe, Anna, et al. (författare)
  • Continuous-Emission Markov Models for Real-Time Applications : Bounding Deadline Miss Probabilities
  • 2023
  • Ingår i: Proc. IEEE Real Time Embedded Technol. Appl. Symp. RTAS. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350321760 ; , s. 14-26
  • Konferensbidrag (refereegranskat)abstract
    • Probabilistic approaches have gained attention over the past decade, providing a modeling framework that enables less pessimistic analysis of real-time systems. Among the different proposed approaches, Markov chains have been shown effective for analyzing real-time systems, particularly in estimating the pending workload distribution and deadline miss probability. However, the state-of-the-art mainly considered discrete emission distributions without investigating the benefits of continuous ones. In this paper, we propose a method for analyzing the workload probability distribution and bounding the deadline miss probability for a task executing in a reservation-based server, where execution times are described by a Markov model with Gaussian emission distributions. The evaluation is performed for the timing behavior of a Kalman filter for Furuta pendulum control. Deadline miss probability bounds are derived with a workload accumulation scheme. The bounds are compared to 1) measured deadline miss ratios of tasks running under the Linux Constant Bandwidth Server with SCHED-DEADLINE, 2) estimates derived from a Markov Model with discrete-emission distributions (PROSIT), 3) simulation-based estimates, and 4) an estimate assuming independent execution times. The results suggest that the proposed method successfully upper bounds actual deadline miss probabilities. Compared to the discrete-emission counterpart, the computation time is independent of the range of the execution times under analysis, and resampling is not required.
  •  
25.
  • Hariharan, Sheela, et al. (författare)
  • On In-Vehicle Network Security Testing Methodologies in Construction Machinery
  • 2022
  • Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9781665499965
  • Konferensbidrag (refereegranskat)abstract
    • In construction machinery, connectivity delivers higher advantages in terms of higher productivity, lower costs, and most importantly safer work environment. As the machinery grows more dependent on internet-connected technologies, data security and product cybersecurity become more critical than ever. These machines have more cyber risks compared to other automotive segments since there are more complexities in software, larger after-market options, use more standardized SAE J1939 protocol, and connectivity through long-distance wireless communication channels (LTE interfaces for fleet management systems). Construction machinery also operates throughout the day, which means connected and monitored endlessly. Till today, construction machinery manufacturers are investigating the product cybersecurity challenges in threat monitoring, security testing, and establishing security governance and policies. There are limited security testing methodologies on SAE J1939 CAN protocols. There are several testing frameworks proposed for fuzz testing CAN networks according to [1]. This paper proposes security testing methods (Fuzzing, Pen testing) for in-vehicle communication protocols in construction machinery.
  •  
26.
  • Hariharan, Sheela, et al. (författare)
  • Towards a holistic approach to security validation of construction machinery through HIL systems
  • 2023
  • Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
  • Konferensbidrag (refereegranskat)abstract
    • The construction industry is increasingly equipping its machinery with sophisticated embedded systems and modern connectivity. Technology advancements in connected safety-critical systems are complex, with cyber-security becoming a more critical factor. Due to interdependencies and network connectivity, attack surfaces and vulnerabilities have increased significantly. Consequently, it is imperative to perform a risk assessment and implement robust security testing methods in order to prevent cyber-attacks on machinery segments. This paper presents a method for identifying potential security threats that also affect machine functional safety, facilitated by identifying threats in the threat modeling process and analyzing safety-security synergies. By identifying such risks, attack scenarios are created to simulate cyber-attacks and create test cases for validation. This approach integrates security testing into the current testing process by using penetration testing tools and utilizing a Hardware-in-the-Loop(HIL) test setup and it is verified with a simulated Denial of Service attack over a CAN network.
  •  
27.
  • Johansson, B., et al. (författare)
  • Consistency before Availability : Network Reference Point based Failure Detection for Controller Redundancy
  • 2023
  • Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
  • Konferensbidrag (refereegranskat)abstract
    • Distributed control systems constitute the automation solution backbone in domains where downtime is costly. Redundancy reduces the risk of faults leading to unplanned downtime. The Industry 4.0 appetite to utilize the device-to-cloud continuum increases the interest in network-based hardware-agnostic controller software. Functionality, such as controller redundancy, must adhere to the new ground rules of pure network dependency. In a standby controller redundancy, only one controller is the active primary. When the primary fails, the backup takes over. A typical network-based failure detection uses a cyclic message with a known interval, a.k.a. a heartbeat. Such a failure detection interprets heartbeat absences as a failure of the supervisee; consequently, a network partitioning could be indistinguishable from a node failure. Hence, in a network partitioning situation, a conventional heartbeat-based failure detection causes more than one active controller in the redundancy set, resulting in inconsistent outputs. We present a failure detection algorithm that uses network reference points to prevent network partitioning from leading to dual primary controllers. In other words, a failure detection that prioritizes consistency before availability.
  •  
28.
  • Johansson, Bjarne, et al. (författare)
  • Kubernetes Orchestration of High Availability Distributed Control Systems
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Distributed control systems transform with the Industry 4.0 paradigm shift. A mesh-like, network-centric topologyreplaces the traditional controller-centered architecture, enforcing the interest of cloud-, fog-, and edge-computing, where lightweight container-based virtualization is a cornerstone. Kubernetes is a well-known container management system for container orchestration in cloud computing. It is gaining traction inedge- and fog-computing due to its elasticity and failure recovery properties. Orchestrator failure recovery can complement the manual replacement of a failed controller and, combined with controller redundancy, provide a pseudo-one-out-of-many redundancy. This paper investigates the failure recovery performance obtained from an out-of-the-box Kubernetes installation in a distributed control system scenario. We describe a Kubernetes based virtualized controller architecture and the software needed to setup a bare-metal cluster for control systems. Further, we deploy single and redundant configured containerized controllers based on an OPC UA compatible industry middleware software on the bare-metal cluster. The controllers expose variables with OPCUA PubSub. A script-based daemon introduces node failures, and a verification controller measures the downtime when using Kubernetes with an industry redundancy solution
  •  
29.
  • Johansson, Bjarne, et al. (författare)
  • Kubernetes Orchestration of High Availability Distributed Control Systems
  • 2022
  • Ingår i: Proc IEEE Int Conf Ind Technol. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728119489
  • Konferensbidrag (refereegranskat)abstract
    • Distributed control systems transform with the Industry 4.0 paradigm shift. A mesh-like, network-centric topology replaces the traditional controller-centered architecture, enforcing the interest of cloud-, fog-, and edge-computing, where lightweight container-based virtualization is a cornerstone. Kubernetes is a well-known container management system for container orchestration in cloud computing. It is gaining traction in edge- and fog-computing due to its elasticity and failure recovery properties. Orchestrator failure recovery can complement the manual replacement of a failed controller and, combined with controller redundancy, provide a pseudo-one-out-of-many redundancy. This paper investigates the failure recovery performance obtained from an out-of-the-box Kubernetes installation in a distributed control system scenario. We describe a Kubernetes based virtualized controller architecture and the software needed to set up a bare-metal cluster for control systems. Further, we deploy single and redundant configured containerized controllers based on an OPC UA compatible industry middleware software on the bare-metal cluster. The controllers expose variables with OPC UA PubSub. A script-based daemon introduces node failures, and a verification controller measures the downtime when using Kubernetes with an industry redundancy solution.
  •  
30.
  • Johansson, Bjarne, et al. (författare)
  • Partible State Replication for Industrial Controller Redundancy
  • 2024
  • Ingår i: Proceedings of the IEEE International Conference on Industrial Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350340266
  • Konferensbidrag (refereegranskat)abstract
    • Distributed control systems are part of the often invisible backbone of modern society that provides utility services like water and electricity. Their uninterrupted operation is vital, and unplanned stops due to failure can be expensive. Critical devices, like controllers, are often duplicated to minimize the service stop probability, with a secondary controller acting as a backup to the primary. A seamless takeover requires that the backup has the primary's latest state, i.e., the primary has to replicate its state to the backup. While this method ensures high availability, it can be costly due to hardware doubling. This work proposes a state replication solution that doesn't require the backup to store the primary state, separating state storage from the backup function. Our replication approach allows for more flexible controller redundancy deployments since one controller can be a backup for multiple primaries without being saturated by state replication data. Our main contribution is the partible state replication approach, realized with a distributed architecture utilizing a consensus algorithm. A partial connectivity-tolerant consensus algorithm is also an additional contribution.
  •  
31.
  • Johansson, Bjarne, et al. (författare)
  • Priority Based Ethernet Handling in Real-Time End System with Ethernet Controller Filtering
  • 2022
  • Ingår i: IECON 2022 – 48th Annual Conference of the IEEE Industrial Electronics Society. - 9781665480253
  • Konferensbidrag (refereegranskat)abstract
    • This work addresses the impact of best-effort traffic on network-dependent real-time functions in distributed control systems. Motivated by the increased Ethernet use in real-time dependent domains, such as the automation industry, a growth driven by Industry 4.0, interconnectivity desires, and data thirst. Ethernet allows different network-based functions to converge on one physical network infrastructure. In the automation domain, converged networks imply that functions with different criticality and real-time requirements coexist and share the same physical resources. The IEEE 60802 Time-Sensitive Networking profile for Industrial Automation targets the automation industry and addresses Ethernet network determinism on converged networks. However, the profile is still in the draft stage at the time of writing this paper. Meanwhile, Ethernet already provides attributes utilized by network equipment to prioritize time-critical communication. This paper shows that Ethernet Controller filtering with prioritized processing is a prominent solution for preserving real-time guarantees while supporting best-effort traffic. A solution capable of eliminating all best-effort traffic interference in the real-time application is exemplified and evaluated on a VxWorks system.
  •  
32.
  • Khalilzad, Nima, 1986- (författare)
  • Adaptive Hierarchical Scheduling Framework for Real-Time Systems
  • 2013
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Modern computer systems are often designed to play a multipurpose role. Therefore, they are capable of running a number of software tasks (software programs) simultaneously in parallel. These software tasks should share the processor such that all of them run and finish their computations as expected. On the other hand, a number of software tasks have timing requirements meaning that they should not only access the processing unit, but this access should also be in a timely manner. Thus, there is a need to timely share the processor among different software programs (applications). The time-sharing often is realized by assigning a fixed and predefined processor time-portion to each application. However, there exists a group of applications where, i) their processor demand is changing in a wide range during run-time, and/or ii) their occasional timing violations can be tolerated. For systems that contain applications with the two aforementioned properties, it is not efficient to assign the applications with fixed processor time-portions. Because, if we allocate the processor resource based on the maximum resource demand of the applications, then the processor's computing capacity will be wasted during the time intervals where the applications will require a smaller portion than maximum resource demand. To this end, in this thesis we propose adaptive processor time-portion assignments. In our adaptive scheme, at each point in time, we monitor the actual demand of the applications, and we provide sufficient processor time-portions for each application. In doing so, we are able to integrate more applications on a shared and resource constrained system, while at the same time providing the applications with timing guarantees.
  •  
33.
  • Lager, Anders, et al. (författare)
  • A Scalable Heuristic for Mission Planning of Mobile Robot Teams
  • 2023
  • Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 9781713872344 ; , s. 7865-7872
  • Konferensbidrag (refereegranskat)abstract
    • In this work, we investigate a task planning problem for assigning and planning a mobile robot team to jointly perform a kitting application with alternative task locations. To this end, the application is modeled as a Robot Task Scheduling Graph and the planning problem is modeled as a Mixed Integer Linear Program (MILP). We propose a heuristic approach to solve the problem with a practically useful performance in terms of scalability and computation time. The experimental evaluation shows that our heuristic approach is able to find efficient plans, in comparison with both optimal and non-optimal MILP solutions, in a fraction of the planning time.
  •  
34.
  • Lager, Anders, et al. (författare)
  • Task Roadmaps: Speeding Up Task Replanning : Corrigendum
  • 2022
  • Ingår i: Frontiers in Robotics and AI. - : Frontiers Media S.A.. - 2296-9144. ; 9
  • Tidskriftsartikel (refereegranskat)abstract
    • In the original article, Listings 1 and 2 were not included during the typesetting process and were overlooked during production. The missing listings appear below. 
  •  
35.
  • Leander, Björn, 1978-, et al. (författare)
  • Dependability and Security Aspects of Network-Centric Control
  • 2023
  • Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
  • Konferensbidrag (refereegranskat)abstract
    • Industrial automation and control systems are responsible for running our most important infrastructures, providing electricity and clean water, producing medicine and food, along with many other services and products we take for granted. The safe and secure operation of these systems is therefore of great importance.One of the emerging trends in industrial automation systems is the transition from static hierarchical controller-centric systems to flexible network-centric systems. This transition has a great impact on the characteristics of industrial automation systems. In this article we describe the network-centric design strategy for industrial automation systems and describe the impact on dependability and security aspects that this strategy brings, looking at both challenges and possibilities.
  •  
36.
  • Liu, Meng (författare)
  • On Improving Resource Utilization in Distributed Real-Time Embedded Systems
  • 2014
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In our modern life, embedded systems are playing an essential role. An embedded system is a computer system embedded into a certain device, in order to achieve computing functions. Beyond all doubt, as a validated system, the functional correctness must be guaranteed. However, for many embedded systems, timeliness also plays an important role in addition to the correctness of the functionalities. For example, in an automotive braking system, the braking function needs to be processed within a limited time duration in order to avoid accidents. Such systems are known as real-time embedded systems.In these systems, there can be plenty of software programs (called tasks) sharing limited computing resources (e.g. processors, memories). If the system executes tasks in a random way, the whole system will become unpredictable. As a result, the system designers will not be able to verify if the system design can fulfill all the timing requirements or not. In other words, the system is not guaranteed to be safe. Therefore, system designers need to carefully implement algorithms to schedule all the tasks in a predictable manner. Regarding each scheduling algorithm, schedulability analyses are proposed which are used to check if the requirements can be satisfied.Unfortunately, many real-time systems reserve too much computing resource for the sake of fulfilling timing requirements, without taking into account resource utilization. As a result, system resources cannot be efficiently utilized, which can cause significant resource waste in reality. Therefore, in this thesis, we aim to improve resource utilization in modern distributed real-time embedded systems. We try to tackle this problem from the following two aspects.Investigating tighter timing analyses. Due to the difficulty in performing precise mathematical schedulability analyses, most of the existing analyses include varying degrees of pessimism. In other words, the actual performance of the system can be much better than the predictions. If we can reduce the pessimism in schedulability analyses, we can then admit more workload into the system.Proposing new scheduling frameworks. It is difficult to find a scheduling algorithm which is suitable for all the situations. Therefore, we need different mechanisms to handle specific system characteristics in order to improve the resource utilization. 
  •  
37.
  • Liu, Meng (författare)
  • Real-Time Communication over Wormhole-Switched On-Chip Networks
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In a modern industrial system, the requirement on computational capacity has increased dramatically, in order to support a higher number of functionalities, to process a larger amount of data or to make faster and safer run-time decisions. Instead of using a traditional single-core processor where threads can only be executed sequentially, multi-core and many-core processors are gaining more and more attentions nowadays. In a multi-core processor, software programs can be executed in parallel, which can thus boost the computational performance. Many-core processors are specialized multi-core processors with a larger number of cores which are designed to achieve a higher degree of parallel processing. An on-chip communication bus is a central intersection used for data-exchange between cores, memory and I/O in most multi-core processors. As the number of cores increases, more contention can occur on the communication bus which raises a bottleneck of the overall performance. Therefore, in order to reduce contention incurred on the communication bus, a many-core processor typically employs a Network-on-Chip (NoC) to achieve data-exchange. Real-time embedded systems have been widely utilized for decades. In addition to the correctness of functionalities, timeliness is also an important factor in such systems. Violation of specific timing requirements can result in performance degradation or even fatal problems. While executing real-time applications on many-core processors, the timeliness of a NoC, as a communication subsystem, is essential as well. Unfortunately, many real-time system designs over-provision resources to guarantee the fulfillment of timing requirements, which can lead to significant resource waste. For example, analysis of a NoC design yields that the network is already saturated (i.e. accepting more traffic can incur requirement violation), however, in reality the network actually has the capacity to admit more traffic. In this thesis, we target such resource wasting problems related to design and analysis of NoCs that are used in real-time systems. We propose a number of solutions to improve the schedulability of real-time traffic over wormhole-switched NoCs in order to further improve the resource utilization of the whole system. The solutions focus mainly on two aspects: (1) providing more accurate and efficient time analyses; (2) proposing more cost-effective scheduling methods.
  •  
38.
  • Markovic, Filip, et al. (författare)
  • Analytical Approximations in Probabilistic Analysis of Real-Time Systems
  • 2022
  • Ingår i: REAL-TIME SYSTEMS SYMPOSIUM/IEEE Computer Society. - : Institute of Electrical and Electronics Engineers Inc.. - 1052-8725. ; 2022-December, s. 158-171
  • Tidskriftsartikel (refereegranskat)abstract
    • Probabilistic timing and schedulability analysis of real-time systems is constrained by the problem of often intractable exact computations. The intractability problem is present whenever there is a large number of entities to be analysed, e.g., jobs, tasks, etc. In the last few years, the analytical approximations for deadline-miss probability emerged as an important solution in the above problem domain. In this paper, we explore analytical solutions for two major problems that are present in the probabilistic analysis of real-time systems. First, for a safe approximation of the entire probability distributions (e.g., of the accumulated execution workloads) we show how the Berry-Esseen theorem can be used. Second, we propose an approximation built on the Berry-Esseen theorem for efficient computation of the quantile functions of probability execution distributions. We also show the asymptotic bounds on the execution distribution of the fixed-priority preemptive tasks. In the evaluation, we investigate the complexity and accuracy of the proposed methods as the number of analysed jobs and tasks increases. The methods are compared with the circular convolution approach. We also investigate the memory footprint comparison between the proposed Berry-Esseen-based solutions and the circular convolution.. The contributions and results presented in this paper complement the state-of-the-art in accurate and efficient probabilistic analysis of real-time systems.
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39.
  • Miloradović, Branko, 1987-, et al. (författare)
  • Challenges in the Automated Disassembly Process of Electric Vehicle Battery Packs
  • 2023
  • Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
  • Konferensbidrag (refereegranskat)abstract
    • The surge in the development and adoption of Electric Vehicles (EVs) globally is a trend many countries are paying close attention to. This inevitably means that a significant number of EV batteries will soon reach their End-of-Life (EoL). This looming issue reveals a notable challenge: there's currently a lack of sustainable strategies for managing Lithium-ion Batteries (LiBs) when they reach their EoL stage. The process of disassembling these battery packs is challenging due to their intricate design, involving several different materials and components integrated tightly for performance and safety. Consequently, effective disassembly and subsequent recycling procedures require highly specialized methods and equipment, and involve significant safety and health risks. Moreover, existing recycling technologies often fail to recover all valuable and potentially hazardous materials, leading to both economic and environmental loss. This paper provides an overview and analysis of possible challenges arising in the domain of automated battery disassembly and recycling of EV batteries that reached their EoL. We provide insight into the disassembly process as well as optimization of the disassembly sequence with the goal of minimizing the overall cost and environmental footprint.
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40.
  • Momeni, Mahdi, et al. (författare)
  • On the Bar Installation Order for the Automated Fabrication of Rebar Cages
  • 2022
  • Ingår i: Proceedings of the International Symposium on Automation and Robotics in Construction. - : International Association for Automation and Robotics in Construction (IAARC). - 9789526952420 ; , s. 508-511
  • Konferensbidrag (refereegranskat)abstract
    • Robotics automation is a promising solution for the fabrication of structures made out of reinforced concrete. The reinforcement is often installed directly in the form and barby-bar. Using bigger pre-fabricated units (cages) may be beneficial for saving construction time and better labor safety. In this paper, we focus on the problem of automating the generation of a plan for the installation of rebars, given the digital twin of a desired reinforcement cage design, and of its basic components. More specifically, the plan describes the assembling order for the rebars such that (i) it is possible to fabricate the reinforcement cage by the robots, and (ii) the end product is the final reinforcement cage, ready for installation in the form for the concrete structure. In this paper, we propose an algorithm to automatically compute a feasible installation order for a generic rebar cage. The feasibility of the generated order is also case studied and simulated on a simplified rebar cage under the given assumptions. 
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41.
  • Salman Shaik, Mohammad, et al. (författare)
  • Dispatching Deadline Constrained Jobs in Edge Computing Systems
  • 2023
  • Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
  • Konferensbidrag (refereegranskat)abstract
    • The edge computing paradigm extends the architectural space of real-time systems by bringing the capabilities of the cloud to the edge. Unlike cloud-native systems designed for mean response times, real-time industrial embedded systems are designed to control a single physical system, such as a manipulator arm or a mobile robot, that requires temporal predictability. We consider the problem of dispatching and scheduling of jobs with deadlines that can be offloaded to the edge and propose DAL, a deadline-aware load balancing and scheduling framework that leverages the availability of on-demand computing resources along with an on-arrival dispatching scheme to manage temporal requirements of such offloaded applications. The evaluation indicates that DAL can achieve reasonably good performance even when execution times, arrival times, and deadlines vary.
  •  
42.
  • Salman Shaik, Mohammad, et al. (författare)
  • Evaluating Dispatching and Scheduling Strategies for Firm Real-Time Jobs in Edge Computing
  • 2023
  • Ingår i: IECON Proc. - : IEEE Computer Society. - 9798350331820
  • Konferensbidrag (refereegranskat)abstract
    • We consider the problem of on-arrival dispatching and scheduling jobs with stochastic execution times, inter-arrival times, and deadlines in multi-server fog and edge computing platforms. In terms of mean response times, it has been shown that size-based scheduling policies, when combined with dispatching policies such as join-shortest-queue, provide better performance over policies such as first-in-first-out. Since job sizes may not always be known apriori, prediction-based policies have been shown to perform reasonably well. However, little is known about the performance of prediction-based policies for jobs with firm deadlines. In this paper, we address this issue by considering the number of jobs that complete within their deadlines as a performance metric and investigate, using simulations, the performance of a prediction-based shortest-job-first scheduling policy for the considered metric and compare it against scheduling policies that prioritize based on deadlines (EDF) and arrival times (FIFO). The evaluation indicates that in under-loaded conditions, the prediction-based policy is outperformed by both FIFO and EDF policies. However, in overloaded scenarios, the prediction-based policy offers slightly better performance.
  •  
43.
  • Salman Shaik, Mohammad (författare)
  • Integrating Elastic Real-Time Applications on Fog Computing Platforms
  • 2022
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Real-time systems such as industrial robots and autonomous navigation vehicles integrate a wide range of algorithms to achieve their functional behavior. In certain systems, these algorithms are deployed on dedicated single-core hardware platforms that exchange information over a real-time network. With the availability of current multi-core platforms, there is growing interest in an integrated architecture where these algorithms can run on a shared hardware platform. In addition, the benefits of virtualization-based cloud and fog architectures for non-real-time applications have prompted discussions about the possibility of achieving similar benefits for real-time systems. Although many useful solutions such as resource reservations and hierarchical scheduling have been proposed to facilitate hardware virtualization for real-time applications, the current state of the art is mainly concerned with applications whose timing requirements can be modelled according to the periodic or the sporadic task model. Since the computational demand of many real-time algorithms can be flexibly adjusted at runtime, e.g., by changing the periods, they can be better abstracted with the elastic task model in the context of virtualized hardware platforms.Therefore, in this thesis, we first propose a scheduling framework with reservations based on periodic resource supply for real-time elastic applications with single-core workloads, and then extend this solution for applications with multi-core workloads  where reservations are based on the minimum-parallelism model. Since many existing applications run on dedicated single-core platforms, we simultaneously provide a systematic methodology for migrating an existing real-time software application from a single-core to a multi-core platform. In doing so, we focus on recovering the architecture of the existing software and transforming it for implementation on a multi-core platform. Next, we explore the advantages of a fog-based architecture over an existing robot control architecture and identify the key research challenges that must be addressed for the adoption of the fog computing architecture.
  •  
44.
  • Salman Shaik, Mohammad, et al. (författare)
  • Scheduling Firm Real-time Applications on the Edge with Single-bit Execution Time Prediction
  • 2023
  • Ingår i: Proc. - IEEE Int. Symp. Real-Time Distrib. Comput., ISORC. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339024 ; , s. 207-213
  • Konferensbidrag (refereegranskat)abstract
    • The edge computing paradigm brings the capabilities of the cloud such as on-demand resource availability to the edge for applications with low-latency and real-time requirements. While cloud-native load balancing and scheduling algorithms strive to improve performance metrics like mean response times, real-time systems, that govern physical systems, must satisfy deadline requirements. This paper explores the potential of an edge computing architecture that utilizes the on-demand availability of computational resources to satisfy firm real-time requirements for applications with stochastic execution and inter-arrival times. As it might be difficult to know precise execution times of individual jobs prior to completion, we consider an admission policy that relies on single-bit execution time predictions for dispatching. We evaluate its performance in terms of the number of jobs that complete by their deadlines via simulations. The results indicate that the prediction-based admission policy can achieve reasonable performance for the considered settings.
  •  
45.
  • Shamseddine, Maha, et al. (författare)
  • NODEGUARD : A Virtualized Introspection Security Approach for the Modern Cloud Data Center
  • 2022
  • Ingår i: 2022 22ND IEEE/ACM INTERNATIONAL SYMPOSIUM ON CLUSTER, CLOUD AND INTERNET COMPUTING (CCGRID 2022). - : IEEE COMPUTER SOC. - 9781665499569 ; , s. 790-797
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents NODEGUARD, a security approach for detecting and isolating misbehaving Virtual Machines (VMs) in multi-tenant virtualized cloud data centers, based on the Virtual Machine Introspection (VMI) monitoring primitives. NODEGUARD employs a divide-and-conquer strategy that checks logical groups of VMs to ensure the efficiency of the detection mechanisms which opportunistically approaches a complexity of O (log(2)(n)) when there is a relatively low number of hostile VMs. This greatly enhances the algorithmic time complexity of the proposed security system compared to the O(n) complexity achieved by the traditional VMI inspection strategy that checks each VM separately. The approach has been evaluated in a virtualized cloud environment using the Mininet network emulator.
  •  
46.
  • van de Vegte, Yordi, et al. (författare)
  • Genetic insights into resting heart rate and its role in cardiovascular disease
  • 2023
  • Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The genetics and clinical consequences of resting heart rate (RHR) remain incompletely understood. Here, the authors discover new genetic variants associated with RHR and find that higher genetically predicted RHR decreases risk of atrial fibrillation and ischemic stroke. Resting heart rate is associated with cardiovascular diseases and mortality in observational and Mendelian randomization studies. The aims of this study are to extend the number of resting heart rate associated genetic variants and to obtain further insights in resting heart rate biology and its clinical consequences. A genome-wide meta-analysis of 100 studies in up to 835,465 individuals reveals 493 independent genetic variants in 352 loci, including 68 genetic variants outside previously identified resting heart rate associated loci. We prioritize 670 genes and in silico annotations point to their enrichment in cardiomyocytes and provide insights in their ECG signature. Two-sample Mendelian randomization analyses indicate that higher genetically predicted resting heart rate increases risk of dilated cardiomyopathy, but decreases risk of developing atrial fibrillation, ischemic stroke, and cardio-embolic stroke. We do not find evidence for a linear or non-linear genetic association between resting heart rate and all-cause mortality in contrast to our previous Mendelian randomization study. Systematic alteration of key differences between the current and previous Mendelian randomization study indicates that the most likely cause of the discrepancy between these studies arises from false positive findings in previous one-sample MR analyses caused by weak-instrument bias at lower P-value thresholds. The results extend our understanding of resting heart rate biology and give additional insights in its role in cardiovascular disease development.
  •  
47.
  • Vitucci, Carlo, 1967- (författare)
  • The role of fault management in the embedded system design
  • 2024
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In the last decade, the world of telecommunications has seen the value ofservices definitively affirmed and the loss of the connectivity value. This changeof pace in the use of the network (and available hardware resources) has ledto continuous, unlimited growth in data traffic, increased incomes for serviceproviders, and a constant erosion of operators’ incomes for voice and ShortMessage Service (SMS) traffic.The change in mobile service consumption is evident to operators. Themarket today is in the hands of over the top (OTT) media content deliverycompanies (Google, Meta, Netflix, Amazon, etc.), and The fifth generation ofmobile networks (5G), the latest generation of mobile architecture, is nothingother than how operators can invest in system infrastructure to participate in theprosperous service business.With the advent of 5G, the worlds of cloud and telecommunications havefound their meeting point, paving the way for new infrastructures and ser-vices, such as smart cities, industry 4.0, industry 5.0, and Augmented Reality(AR)/Virtual Reality (VR). People, infrastructures, and devices are connected toprovide services that we even struggle to imagine today, but a highly intercon-nected system requires high levels of reliability and resilience.Hardware reliability has increased since the 1990s. However, it is equallycorrect to mention that the introduction of new technologies in the nanometerdomain and the growing complexity of on-chip systems have made fault man-agement critical to guarantee the quality of the service offered to the customerand the sustainability of the network infrastructure.In this thesis, our first contribution is a review of the fault managementimplementation framework for the radio access network domain. Our approachintroduces a holistic vision in fault management where there is increasingly moresignificant attention to the recovery action, the crucial target of the proposedframework. A new contribution underlines the attention toward the recoverytarget: we revisited the taxonomy of faults in mobile systems to enhance theresult of the recovery action, which, in our opinion, must be propagated betweenthe different layers of an embedded system ( hardware, firmware, middleware,and software). The practical adoption of the new framework and the newtaxonomy allowed us to make a unique contribution to the thesis: the proposalof a new algorithm for managing system memory errors, both temporary (soft)and permanent (hard)The holistic vision of error management we introduced in this thesis involveshardware that proactively manages faults. An efficient implementation of faultmanagement is only possible if the hardware design considers error-handlingtechniques and methodologies. Another contribution of this thesis is the def-inition of the fault management requirements for the RAN embedded systemhardware design.Another primary function of the proposed fault management framework isfault prediction. Recognizing error patterns means allowing the system to reactin time, even before the error condition occurs, or identifying the topology of theerror to implement more targeted and, therefore, more efficient recovery actions.The operating temperature is always a critical characteristic of embedded radioaccess network systems. Base stations must be able to work in very differenttemperature conditions. However, the working temperature also directly affectsthe probability of error for the system. In this thesis, we have also contributed interms of a machine-learning algorithm for predicting the working temperature ofbase stations in radio access networks — a first step towards a more sophisticatedimplementation of error prevention and prediction.
  •  
48.
  • Åsberg, Mikael (författare)
  • On the Development of Hierarchical Real-Time Systems
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Hierarchical scheduling (also referred to as resource reservation) is a hot topic within the research of real-time systems. It has many advantages such that it can facilitate software integration, fault isolation, structured analysis, legacy system integration etc. The main idea is to partition resources into well defined slots and the resource itself may be the processor, memory etc. This technique is rarely used in real-time applications, however, it is well adopted in the avionics industry in order to isolate error propagation between system parts, and facilitate analysis of the system.Much of the research within resource reservation deals with theoretical schedulability analysis of partitioned systems, including shared resources (other than the processor). We will in this thesis address more practical issues related to resource reservation. We focus on implementation and prototyping aspects, as well as verification and instrumentation. One of our assumptions is that we deal only with fixed-priority preemptive scheduling (FPPS).The first part in this thesis deals with individual software systems that may have its own tasks as well as a scheduler and it is assumed to be part of another larger system, hence, we refer to this individual system as a subsystem. The subsystem is assumed to be integrated together with other subsystems, but at a early stage, we make it possible to simulate the subsystem running together with the rest of the subsystems. This "simulation`` does not require the actual resource reservation mechanism, the only requirement is an operating system with support for FPPS. This pre-study may be a natural step towards the "real`` integration, since each individual subsystem can be test executed within its assigned partition. All subsystems are assumed to run together using a resource reservation mechanism (during the actual integration). We have developed two prototypes of this mechanism. The first prototype is hand-crafted and it is equipped with a program tracer for partitoned based schedulers. This instrumentation is useful for debugging and visualization of program traces for this type of scheduling. The second prototype is developed using timed automata with tasks (task automata). This model-based scheduler is verified for correctness and it is possible to automatically generate source code for the scheduler. We have successfully synthesized this scheduler for the real-time operating system VxWorks. However, it can easily be executed on most other platforms. Both prototypes has pros and cons. The first version has good performance while the second can guarantee its correctness, hence, there is a trade-off between performance and correctness.
  •  
49.
  • Åsberg, Mikael (författare)
  • Synthesis and Synchronization Support for Hierarchically Scheduled Real-Time Systems
  • 2014
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • A piece of software, that we define as a software system, can consist of anything from a few lines of program code or the entire software stack in a vehicle. Software systems can be divided into smaller and partially independent parts called subsystems/partitions (we use the words partition and subsystem interchangeably). The non-functional isolation of subsystems, that appears when the software system is hierarchically divided, has great advantages when it comes to preventing fault propagation between subsystems. The hierarchical division, that we refer to as hierarchical scheduling, has other advantages as well. It facilitates re-usability and it makes timing analysis of software systems easier. Hierarchical scheduling has been shown to be a useful tool in counteracting the verification challenges that comes from the growing complexity in software. For example, the avionics-specification ARINC653 and the safety-critical operating systems seL4 and PikeOS safely divide resources for independent safety-critical applications by using hierarchical scheduling.Hierarchical scheduling can be implemented in many different ways, depending on what resource that is supposed to be shared among applications. The resource could be the CPU, memory, network etc. The work in this thesis is focused on the practical aspects of timing isolation among subsystems, i.e., sharing of the CPU resource. Hence, this work elaborates on how to adapt and extend the operating-system task-scheduler to support hierarchical scheduling. We have focused on both independent and semi-dependent subsystems. Independent subsystems only share general resources such as the CPU and memory. Semi-independent subsystems share not only the general resources, but also other logical resources that can only be accessed in a mutually exclusive way, i.e., by one subsystem at a time. An example of such a resource could be a shared memory-space, e.g., a database, a memory-mapped device etc.This thesis has two main parts related to hierarchical scheduling: scheduler synthesis, and synchronization.Scheduler synthesis is related to implementation and design strategies when adding support for hierarchical scheduling in an operating system. We have focused on various operating systems that were lacking the feature of hierarchical scheduling. The two most interesting operating systems that we worked on was Linux and seL4. These two operating systems represent two extremes, where Linux is more focused towards soft real-time systems and seL4 towards pure hard real-time (safety-critical) systems. Linux-based systems have in general less strict demands on correctness and more requirements on usability. Usability implies less installation efforts and less limitations in the usage of the available Linux functionality. The usability aspect is especially important for Linux systems since kernel updates occur much more frequently compared to any other operating system. Hence, extending/modifying the functionality of Linux must be done in a way that does not require any modifications to the kernel. seL4 on the other hand has strict requirements on safety, i.e., functional and non-functional correctness, but also performance efficiency. Guaranteeing correctness implies a potential loss of performance due to the added overhead that the verified software can bring. The correctness aspect includes strategies on how to verify hierarchical schedulers, but also how to minimize the scheduler overhead and achieve as good run-time performance as possible. Conclusively, there are many challenges when it comes to scheduler synthesis. There are requirements on performance, usability, correctness etc. The contribution in the synthesis part includes a scheduler framework called ExSched (External Scheduler). We have also contributed with a novel approach to verify hierarchical schedulers, and a code generator called TAtoC (Timed Automata to C) which contributes to the effective run-time performance of synthesized timed-automata models.The second part of this thesis, synchronization, is an important general aspect of hierarchically scheduled systems since the isolation of subsystems makes resource sharing among subsystems more challenging. We have advanced the state-of-the-art in this research area by introducing a new synchronization protocol called RRP (Rollback Resource Policy) that improves on the robustness and run-time performance compared to the existing protocols. We have also conducted a large scale experimental evaluation of all existing protocols that we have implemented in the widely used real-time operating system VxWorks.
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