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Challenges associated with allowing preemptions and migrations are compounded in multicore systems, particularly under global scheduling policies, because of the potentially high overheads. For example, multiple levels of cache greatly increase preemption and migration related overheads as well as the difficulty involved in accurately accounting for them, leading to substantially inflated worst-case execution times. Preemption and migrations related overheads can be significantly reduced, both in number and in size, by using fixed preemption points in the tasks' code; thus dividing each task into a series of non-preemptive regions. This leads to an additional consideration in the scheduling policy. When a high priority task is released and all of the processors are executing non-preemptive regions of lower priority tasks, then there is a choice to be made in terms of how to manage the next preemption. With an eager approach the first lower priority task to reach a preemption point is preempted even if it is not the lowest priority running task. Alternatively, with a lazy approach, preemption is delayed until the lowest priority currently running task reaches its next preemption point. In this paper, we show that under global fixed priority scheduling with eager preemptions each task suffers from at most a single priority inversion each time it resumes execution. Building on this observation, we derive a new response time based schedulability test for tasks with fixed preemption points. Experimental evaluations show that global fixed priority scheduling with eager preemptions is significantly more effective than with lazy preemption using link based scheduling in terms of task set schedulability.

CONTESSE - Contract-Based Components for Embedded Software

Adopting mixed-criticality architectures enable safe sharing of computational resources between tasks of different criticalities consequently leading to reduced Size, Weight and Power (SWaP) requirements. A majority of the research in mixed-criticality systems focuses on scheduling tasks whose Worst Case Execution Times (WCETs) are certified to varying levels of assurances. If any given task overruns its WCET, the system switches to a higher criticality and all the lower criticality tasks are discarded to make time for the execution of higher criticality tasks. Task execution time overruns are transient faults that are typically tolerated by simply executing an alternate task before the original deadline, or, by discarding the failed task to prevent it from interfering with higher criticality tasks. However, permanent faults such as processor failures can render the system to be useless, many times leading to unsafe states. In this paper we present a taxonomy of fault tolerance techniques to tolerate permanent faults, as well as map it to real-time mixed-criticality requirements based on the extend of fault coverage that in turn influences the associated assurance.

Most of the critical challenges seen in the past decades have impacted citizens in a global way. Given shrinking resources, educationists find preparing students for the global market place a formidable challenge. Hence exposing students to multi-lateral educational initiatives are critical to their growth, understanding and future contributions. This paper focuses on European Union's Erasmus Mundus programs, involving academic cooperation amongst international universities in engineering programs. A phased undergraduate engineering program with multiple specializations is analyzed within this context. Based on their performance at the end of first phase, selected students were provided opportunities using scholarship to pursue completion of their degree requirements at various European universities. This paper will elaborate the impact of differing pedagogical interventions, language and cultural differences amongst these countries on students in diverse engineering disciplines. The data presented is based on on the feedback analysis from Eramus Mundus students (N=121) that underwent the mobility programs. The findings have given important insights into the structure of the initiative and implications for academia and education policy makers for internationalizing engineering education. These included considering digital interventions such as MOOCs (Massive Open Online Courses) and Virtual Laboratory (VL) initiatives for systemic reorganization of engineering education.

Today's industrial product lines in the automotive and construction equipment domain face the challenge to show functional safety standard compliance and argue for the absence of failures for all derived product variants. The product line approaches are not su cient to support practitioners to trace safety-related characteristics through development. We aim to provide aid in creating a safety case for a certain con guration in a product line such that overall less e ort is necessary for each con guration. In this paper we 1) discuss the impact of functional safety on product line development, 2) propose a model-based approach to capture safety-related characteristics during concept phase for product lines and 3) analyze the usefulness of our proposal., ITS-EASY Post Graduate School for Embedded Software and Systems, SafeCer - Safety Certification of Software-Intensive Systems with Reusable Components

Testing of safety-critical embedded systems is an important and costly endeavor. To date researchers and practitioners have been mainly focusing on the design and application of diverse testing strategies, but leaving the test stopping criteria as an ad hoc decision and an open research issue. In our previous work, we proposed a convergence algorithm that informs the tester when the current testing strategy does not seem to be revealing new insight into the worst-case timing properties of tasks and hence should be stopped. This algorithm was shown to be successful but its trial and error tuning of parameters was an issue. In this paper, we use the Design of Experiment (DOE) approach to optimise the algorithm's performance and to improve its scalability. During our experimental evaluations the optimised algorithm showed improved performance by achieving relatively the same results with 42% less testing cost as compared to our previous work. The algorithm also has better scalability and opens up a new path towards achieving cost effective non-functional testing of real-time embedded systems., SYNOPSIS - Safety Analysis for Predictable Software Intensive Systems

Most of the critical challenges seen in the past decades have impacted citizens in a global way. Given shrinking resources, educationists find preparing students for the global market place a formidable challenge. Hence exposing students to multi-lateral educational initiatives are critical to their growth, understanding and future contributions. This paper focuses on European Union's Erasmus Mundus programs, involving academic cooperation amongst international universities in engineering programs. A phased undergraduate engineering program with multiple specializations is analyzed within this context. Based on their performance at the end of first phase, selected students were provided opportunities using scholarship to pursue completion of their degree requirements at various European universities. This paper will elaborate the impact of differing pedagogical interventions, language and cultural differences amongst these countries on students in diverse engineering disciplines. The data presented is based on on the feedback analysis from Eramus Mundus students (N = 121) that underwent the mobility programs. The findings have given important insights into the structure of the initiative and implications for academia and education policy makers for internationalizing engineering education. These included considering digital interventions such as MOOCs (Massive Open Online Courses) and Virtual Laboratory (VL) initiatives for systemic reorganization of engineering education.

Reliability is a key requirement in many distributed real-time systems deployed in safety and mission critical applications, and temporal redundancy is a widely employed strategy towards guaranteeing it. The temporal redundancy approach is typically based on task re-executions in form of entire tasks, task alternates or, check-pointing blocks, and each of the re-execution strategies have different impacts on the Fault Tolerance feasibility (FT-feasibility) of the system, which is traditionally defined as the existence of a schedule that guarantees timeliness of all tasks under a specified fault hypothesis. In this paper, we propose the use of resource augmentation to quantify the FT-feasibility of real-time task sets and use it to derive limits on the effectiveness of temporal redundancy in fault-tolerant real-time scheduling under error bursts of bounded lengths. We derive the limits for the general case, and then show that for the specific case when the error burst length is no longer than half the shortest deadline, the lower limit on the effectiveness of temporal redundancy is given by the resource augmentation bound 2, while, the corresponding upper-limit is 6. Our proposed approach empowers a system designer to quantify the effectiveness of a particular implementation of temporal redundancy.

Modern safety critical real-time systems are composed of tasks of mixed criticalities and the problem of scheduling them in a fault tolerant manner, on a distributed platform, is challenging. Fault tolerance is typically achieved by using redundancy techniques, most commonly in the form of temporal redundancy which involves executing an alternate task before the original deadline of the failed task. Additionally, studies like Zonal Hazard Analysis (ZHA) and Fault Hazard Analysis (FHA) may impose extra constraints on the re-executions, e.g., spatial separation of alternates, to improve reliability. In this paper, we present a method for scheduling mixed criticality real-time tasks on a distributed platform in a fault tolerant manner while taking into account the recommendations given by the reliability studies like ZHA and FHA. First, we use mathematical optimization to allocate tasks on the processors, and then derive fault tolerant and fault aware feasibility windows for the critical and non-critical tasks respectively. Finally, we derive scheduler specific task attributes like priorities for the fixed priority scheduler. Our method provides hard real-time fault tolerance guarantees for critical tasks while maximizing resource utilization for non-critical tasks.

The product line engineering approach is a promising concept to identify and manage reuse in a structured and efficient way and is even applied for the development of safety critical embedded systems. Managing the complexity of variability and addressing functional safety at the same time is challenging and is not yet solved. Variability management is an enabler to both establish traceability and making necessary information visible for safety engineers. We identify a set of requirements for such a method and evaluate existing variability management methods. We apply the most promising method to an industrial case and study its suitability for developing safety critical product family members. This study provides positive feedback on the potential of the model-based method PLUS in supporting the development of functional safety critical embedded systems in product lines. As a result of our analysis we suggest potential improvements for it.

The feasibility of preemptive and non-preemptivescheduling has been well investigated on uniprocessor and multiprocessor platforms under both Fixed Priority Scheduling(FPS) and Earliest Deadline First (EDF) paradigms. While feasibility of limited preemptive scheduling under FPS has been addressed on both uniprocssor and multiprocessor platforms,under EDF it has been investigated only on uniprocessors, and a similar analysis for multiprocessor platforms is still missing.In this paper, we introduce global Limited Preemptive Earliest Deadline First (g-LP-EDF) scheduling, and propose the associated feasibility analysis to complete the above described feasibility analysis spectrum. Specifically, we derive a sufficient condition that guarantees g-LP-EDF feasibility of sporadic real timetasks which directly provides a global Non-Preemptive Earliest Deadline First (g-NP-EDF) feasibility test. We then study the interplay between g-LP-EDF feasibility and processor speed, in order to quantify the sub-optimality of g-NP-EDF in terms of the minimum speed-up required to guarantee g-NP-EDF feasibility of all feasible tasksets. The results presented in this paper complement our previous results on uniprocessors, and provide a unified result on the sub-optimality of non-preemptive EDF on both uniprocessor and multiprocessor platforms., CONTESSE - Contract-Based Components for Embedded Software

Safety-critical systems (such as those in automotive, avionics, railway domains), where a failure can result in accidents with fatal consequences, need to certify their products as per domain-specific safety standards. Safety certification is not only time consuming but also consumes the project budget. Adopting a reuse oriented development and certification paradigm can be highly beneficial in such systems. Though there had been several research efforts on cost models in the context of software reuse as well as software product lines, none of them have addressed the certification related costs. In this paper, we present a cost model for software product lines, which incorporates certification costs as well. We first propose a mathematical model to represent a Software Product Line and then present an approach to compute, using optimisation theory, the set of artifacts that compose a new product assuring an expected level of confidence (that is, a certain Safety Integrity Level) at an optimised cost level. The proposed approach can help developers and software project managers in making efficient design decisions in relation to the choice of the components for a new product variant development as part of a product line, SYNOPSIS - Safety Analysis for Predictable Software Intensive Systems, SafeCer - Safety Certification of Software-Intensive Systems with Reusable Components

Safety or mission critical applications have to recover from an error within an acceptable time window or it may potentially lead to disastrous effects or higher costs. The usual industrial practice is to employ fault tolerance using hardware redundancy where costs are highly exorbitant depending on the mission. In this paper, we present a framework for adaptive fault tolerance on the commonly used hardware redundancy. This proposed model gives enhanced resource management and improved system performance under normal runtime and provides minimal safe functionality under error conditions. A new scheduling method, a combination of dynamic planning and dynamic best effort approach has been designed for joint scheduling of periodic and aperiodic tasks which also include online reconfiguration for error management. This fault recovery technique allows all critical tasks to meet their deadlines and the system continues functioning with minimal safe functionality upon errors. This model has been analyzed and evaluated on a practical case study of a Cruise Control System vis- à-vis a traditional redundancy scheme with simulation and validated with appropriate performance metrics. The results demonstrate the high performance throughput and process speedup (Execution time of process) that can be gained by applying this model to an m-processor redundancy model and the advantages can be accrued specially in the field of avionics in terms of fuel/weight ratio.

Developing safety critical products demands a clear safety argumentation for each product in spite of whether it has been derived from a product line or not. The functional safety standards do not explain how to develop safety critical products in product lines, and the product line concept is lacking specific approaches to develop safety critical products. Nonetheless, product lines are well-established concepts even in companies developing safety critical products. In this paper we present the results of an exploratory study interviewing 15 practitioners from 6 different companies. We identify typical challenges and approaches from industry and discuss their suitability. The challenges and approaches brought out by this study help us to identify and enhance applicable methods from the product line engineering domain that can meet the challenges in the safety critical domain as well.

Critical systems often use N-modular redundancy to tolerate faults in subsystems. Traditional approaches to N-modular redundancy in distributed, loosely-synchronised, real-time systems handle time and value errors separately: a voter detects value errors, while watchdog-based health monitoring detects timing errors. In prior work, we proposed the integrated Voting on Time and Value (VTV) strategy, which allows both timing and value errors to be detected simultaneously. In this paper, we show how VTV can be harnessed as part of an overall fault tolerance strategy and evaluate its performance using a well-known control application, the Inverted Pendulum. Through extensive simulations, we compare the performance of Inverted Pendulum systems which employs VTV and alternative voting strategies to demonstrate that VTV better tolerates well-recognised faults in this realistically complex control problem.

CONTESSE - Contract-Based Components for Embedded Software

In dependable real-time systems, provision of schedulability guarantees for task sets under realistic fault and error assumptions is an essential requirement, though complex and tricky to achieve. An important factor to be considered in this context is the random nature of occurrences of faults and errors, which, if addressed in the traditional schedulability analysis by assuming a rigid worst case occurrence scenario, may lead to inaccurate results. In this paper we first propose a stochastic fault and error model which has the capability of modeling error bursts in lieu of the commonly used simplistic error assumptions in processor scheduling. We then present a novel schedulability analysis that accounts for a range of worst case scenarios generated by stochastic error burst occurrences on the response times of tasks scheduled under the fixed priority scheduling (FPS) policy. Finally, we describe a methodology for the calculation of probabilistic schedulability guarantees as a weighted sum of the conditional probabilities of schedulability under specified error burst characteristics.

Conducting empirical studies in industry always presents a major challenge for many researchers. Being a graduate student does not make things any easier. Often due to the lack of experience, credibility or just very limited networking, graduate students do not receive many opportunities to directly collaborate with industry and experiment their theoretical models in a realistic environment. On the other hand, empirical research conducted in an academic settings is often criticised for using students as subjects and working with a small sample size, thus creating major validity threat of the published results. In this paper we are presenting an experience report from an industrial empirical study conducted at Infosys Ltd., India with the support of their global internship program for graduate students, InStep. Focus of the paper is to present several challenges arisen before, during, and after the study, requiring an immediate attention in order to have a successful experiment completion. We also discuss and elaborate the data analysis results and its implication to our current research activities.

An effective error handling mechanism plays an important role to ensure the reliability and robustness of the application of controller area network (CAN) in controlling dynamic systems. This paper addresses a new online error handling approach or named per-sample-error-counting (PSeC) technique that tends to replace native error handling protocol in controller area network (CAN). The mechanism is designed to manage transmission errors of both sensor and control data in networked control system (NCS) used in controlling dynamic system such that the stability of the feedback system is preserved. A new parameter denoted as maximum allowable number of error burst (MAEB) is introduced in which MAEB is selected based on available bandwidth of the CAN network. MAEB serves as the maximum number of attempt of re-transmission of erroneous data per sample which allows the maximum transmission period to be known and guaranteed for time-critical control system. The efficacy of the proposed method is verified by applying the algorithm on the fourth order inverted pendulum system simulated on Matlab/Truetime simulator and the performance is benchmarked with the existing CAN error management protocol. The simulation run under various systems conditions demonstrate that the proposed method results in superior system performance in handling data transmission error as well as meeting control system requirement. © 2013 Elsevier B.V.

A number of preemptive real-time scheduling algorithms, such as Earliest Deadline First (EDF), are known to be optimal on uni-processor systems under specified assumptions. However, no uni-processor optimal algorithm exists under the non-preemptive scheduling paradigm. Hence preemptive schemes strictly dominate non-preemptive schemes with respect to uni-processor feasibility. However, the 'goodness' of non-preemptive schemes, compared to uni-processor optimal preemptive scheduling schemes such as EDF, which can also be referred to as its sub-optimality, has not been fully investigated yet. In this paper, we apply resource augmentation, specifically processor speed-up, to quantify the sub-optimality of non-preemptive scheduling with respect to EDF, and apply the results to guarantee user specified upper-bounds on the preemption related scheduling costs. In particular, we derive an upper bound on the minimum processor speed-up required to guarantee the non-preemptive feasibility of tasks that are deemed feasible under the preemptive EDF, and we prove that, in the cases where, for all tasks in the task set, the largest execution requirement is not greater than the shortest deadline, this bound is equal to 4. We also show how the proposed approach enables a system designer to choose an optimal processor, in order to, e.g., guarantee specified upper bounds on the preemption related overheads.

Lean principles, originating from Japanese automotive industry, are anticipated to be useful to improve software development processes. Albeit its popularity there is still no generally accepted, clear and detailed definition of what lean software development actually means. This makes it difficult to perform research on the effects of lean software development and determine its usefulness in various contexts. To fill in that research gap this paper analyzes the state of the art based on 20 key Lean concepts derived from nine seminal sources identified in a systematic literature review. The original explanations of the key concepts have been elaborated further and synthesized into a framework for lean software development consisting of a set of goals, recommended activities and practices. The detailed results for the key concept Value are reported. The proposed framework is expected to serve as a basis for further research and for Lean assessment of organizations., ITS-EASY Post Graduate School for Embedded Software and Systems

Providing contemporary and quality education on fast changing technological areas has always been a major challenge to the academic community. The requirements and challenges faced by the embedded systems educators to cope with the fast-paced changes happening in technological development, learning models and medium of instruction etc. are very much similar to that faced by dependable embedded systems developers. In this context we see a lot of potential for relating and adapting the research efforts undertaken in EU Projects such as SafeCer in using component based development (CBD) approach for building adaptable, certifiable systems at lower costs. We describe some such similarities and contemplate how one could potentially leverage on the approaches and results existing in the CBD world by adopting and adapting them to support efficient curriculum development and management. Such an approach is expected to provide the course developers with immense opportunities for building and sharing their courses beyond the originally targeted community., SYNOPSIS - Safety Analysis for Predictable Software Intensive Systems, SafeCer - Safety Certification of Software-Intensive Systems with Reusable Components

Test driven development (TDD) appears not to be immune to positive test bias effects, as we observed in several empirical studies. In these studies, developers created a significantly larger set of positive tests, but at the same time the number of defects detected with negative tests is significantly higher than those detected by positive ones. In this paper we propose the concept of TDDHQ which is aimed at achieving higher quality of testing in TDD by augmenting the standard TDD with suitable test design techniques. To exemplify this concept, we present combining equivalence partitioning test design technique together with the TDD, for the purpose of improving design of test cases. Initial evaluation of this approach showed a noticeable improvement in the quality of test cases created by developers utilising TDDHQ approach., SYNOPSIS - Safety Analysis for Predictable Software Intensive Systems

The ubiquity of software is making every industry increasingly dependent on it for achieving their core products' functionality. The complexity in a telecommunication network requires not only thorough understanding of telecommunication per se, but software becomes equally interesting. This is the case with many industries, which rely more and more on software as their key enabler. Industry definitely needs a large number of software engineers with potential to be productive from day one. They are feeling impatient at the academic community for not being pragmatic. At the same time Academic community faces many challenges, which often make them thread a traditional path thus ignoring the industrial needs. We present some of these challenges from both the industrial and academic perspectives. We also present how we established a Master level advanced course on software verification and validation through mutual support and collaboration which became highly successful.

Critical distributed real-time embedded component-based systems must be dependable and thus be able to avoid unacceptable failures. To efficiently evaluate the dependability of the assembly obtained by selecting and composing components, well-integrated and tool-supported techniques are needed. Currently, no satisfying tool-supported technique fully integrated in the development life-cycle exists. To overcome this limitation, we propose CHESS-FLA, which is a model-driven failure logic analysis method. CHESS-FLA allows designers to: model the nominal as well as the failure behaviour of their architectures, automatically perform dependability analysis through a model transformation, and, finally, ease the interpretation of the analysis results through back-propagation onto the original architectural model. CHESS-FLA is part of an industrial quality tool-set for the functional and extra-functional development of high integrity embedded component-based systems, developed within the EU-ARTEMIS funded CHESS project. Finally, we present a case study taken from the telecommunication domain to illustrate and assess the proposed method.

Hard real-time applications typically have to satisfy high dependability requirements in terms of fault tolerance in both the value and the time domains. Loosely synchronized real-time systems, which represent many of the systems that are developed, make any form of voting difficult as each replica may provide different outputs independent of whether there has been an error or not. This can also lead to false positives and false negatives which makes achieving fault tolerance, and hence dependability, difficult. We have earlier proposed a majority voting technique, ”Voting on Time and Value” (VTV) that explicitly considers combinations of value and timing errors, targeting loosely synchronised systems. In this paper, we extend VTV to enable voter parameter tuning to obtain the desired user specified trade-offs between the false positive and false negative rates in the voter outputs. We evaluate the performance of VTV against Compare Majority Voting (CMV), which is a known voting approach applicable in similar contexts, through extensive simulation studies. The results clearly demonstrate that VTV outperforms CMV in all scenarios with lower false negative rates.

Electronic systems in the automotive domain implement safety critical functionality in vehicles and the safety certification process according to a functional safety standard is time consuming and a big part of the expenses of a development project. We describe the functional safety certification of electronic automotive systems by presenting a use case from the construction equipment industry. In this context, we highlight some of the major challenges we foresee, while using a product-line approach to achieve efficient functional safety certification of vehicle variants. We further elaborate on the impact of functional safety certification when applying the component-based approach on developing safety critical product variants and discuss the implications by cost modeling and analysis.

Complex software is becoming an important component of modern safety-critical systems. To assure the correct function of such software, the development processes are heavily regulated by international standards, often making the process very rigid, unable to accommodate changes, causing late integration and increasing the cost of development. Agile methods have been introduced to address these issues in several software domains, but their use in safety-critical applications remains to be investigated. This paper provides an initial analysis of agile practices in the context of software development for the European railway sector, regulated by the EN 50128 standard. The study complements previous studies on the use of agile methods in other regulated domains. A systematic mapping between EN 50128 requirements and agile practices showed that all practices support some objectives of the standard. Important supporting features recognized were focus on simple design, test automation, coding standards, continuous integration and validation. However, several problematic areas were also identified, including vague requirement analysis and change management. Most agile practices must be adapted to suit regulated software development and this analysis outlines a subset of the required changes. © 2012 IEEE.

Test-driven development is an essential part of eXtreme Programming approach with the preference of being followed in other Agile methods as well. For several years, researchers are performing empirical investigations to evaluate quality improvements in the resulting code when test-driven development is being used. However, very little had been reported into investigating the quality of the testing performed in conjunction with test-driven development. In this paper we present results from an experiment specifically designed to evaluate the quality of test cases created by developers who used the test-first and the traditional test-last approaches. On an average, the quality of testing in test-driven development was almost the same as the quality of testing using test-last approach. However, detailed analysis of test cases, created by test-driven development group, revealed that 29% of test cases were "negative" test cases (based on non-specified requirements) but contributing as much as 65% to the overall tests quality score of test-first developers. We are currently investigating the possibility of extending test-driven development to facilitate non-specified requirements to a higher extent and thus minimise the impact of a potentially inherent effect of positive test bias.

Background: Test driven development, as a side-effect of developing software, will produce a set of accompanied test cases which can protect implemented features during code refactoring. However, recent research results point out that successful adoption of test driven development might be limited by the testing skills of developers using it. Aim: Main goal of this paper is to investigate if there is a difference between the quality of test cases created while using test-first and test-last approaches. Additional goal of this paper is to measure the code quality produced using test-first and test-last approaches. Method: A pilot study was conducted during the master level course on Software Verification & Validation at Mälardalen University. Students were working individually on the problem implementation by being randomly assigned to a test-first or a test-last (control) group. Source code and test cases created by each participant during the study, as well as their answers on a survey questionnaire after the study, were collected and analysed. The quality of the test cases is analysed from three perspectives: (i) code coverage, (ii) mutation score and (iii) the total number of failing assertions. Results: The total number of test cases with failing assertions (test cases revealing an error in the code) was nearly the same for both test-first and test-last groups. This can be interpreted as "test cases created by test-first developers were as good as (or as bad as) test cases created by test-last developers". On the contrary, solutions created by test-first developers had, on average, 27% less failing assertions when compared to solutions created by the test-last group. Conclusions: Though the study provided some interesting observations, it needs to be conducted as a fully controlled experiment with a higher number of participants in order to validate statistical significance of the presented results.

Dependability is a vital system requirement, particularly in safety critical and mission critical real-time systems, due to the potentially catastrophic consequences of failures. In most critical applications different fault tolerance mechanisms using redundancy are employed to prevent possible failures. In the case of real-time systems the system designer must ensure that the task set is feasible even under faults, which we refer to as 'fault tolerance feasibility'. Due to cost considerations, often temporal redundancy has been prevalently used to meet this objective. In this paper we focus on guaranteeing fault-tolerance feasibility under error bursts on uni-processor systems by the usage of resource augmentation, specifically through processor speed-up. Firstly, we derive a processor demand bound based sufficient condition for a set of real-time tasks to be fault tolerance feasible under an assumption that no more than one error burst occurs during the hyper-period of the task set. Subsequently, we derive the necessary resource augmentation bounds (i.e., the processor speed-up), that guarantees the fault tolerance feasibility, if the sufficient test fails. Finally, we prove that, if the error burst length is no more than half the shortest relative deadline of the task set, the minimum processor speed-up required to guarantee fault tolerance feasibility is upper-bounded by 6.

Preemption related costs are major sources of unpredictability in the task execution times in a real-time system. We examine the possibility of using CPU frequency scaling to control the preemption behavior of real-time sporadic tasks scheduled using a preemptive Fixed Priority Scheduling (FPS) policy. Our combined offline-online method provides probabilistic preemption control guarantees by making use of the release time probabilities of the sporadic tasks. The offline phase derives the probability related deviation from the minimum inter-arrival time of tasks. The online algorithm uses this information to calculate appropriate CPU frequencies that guarantees non-preemptive task executions while preserving the overall system schedulability. The online algorithm has a linear complexity and does not lead to significant implementation overheads. Our evaluations demonstrate the effectiveness of the method as well as the possibility of energy-preemption trade offs. Even though we have considered FPS, our method can easily be extended to dynamic priority scheduling schemes