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Zero-laxity (ZL) and contention-free (CF) policies have received considerable attention owing to their simplicity and applicability to real-time systems equipped with symmetry multiprocessors. Recently, the ZL policy for mixed-criticality (MC) systems has been proposed and studied, but the applicability to and performance of the CF policy for MC systems have not been investigated yet. In this paper, we propose the CF policy (as a scheduling policy) for MC symmetry multiprocessor systems, referred to as the MC systems tailored CF policy (MC-CF), and a schedulability analysis in support thereof. We define the notion of contention-free slots for two different criticalities (of MC systems) of tasks, propose a technique to limit the amount to be utilized for each task by defining an upper bound, and subsequently explain the way in which the contention-free slots are systematically utilized to improve the schedulability of MC symmetry multiprocessor systems. Following this, we develop a deadline analysis (DA) for MC-CF. Using our experimental results under various environmental settings, we demonstrate that MC-CF can significantly improve the schedulability of fixed-priority scheduling.

A timing constraint and a high level of reliability are the fundamental requirements for designing hard real-time systems. To support both requirements, the N modular redundancy (NMR) technique as a fault-tolerant real-time scheduling has been proposed, which executes identical copies for each task simultaneously on multiprocessor platforms, and a single correct one is voted on, if any. However, this technique can compromise the schedulability of the target system during improving reliability because it produces N identical copies of each job that execute in parallel on multiprocessor platforms, and some tasks may miss their deadlines due to the enlarged computing power required for completing their executions. In this paper, we propose task-level N modular redundancy (TL-NMR), which improves the system reliability of the target system of which tasks are scheduled by any fixed-priority (FP) scheduling without schedulability loss. Based on experimental results, we demonstrate that TL-NMR maintains the schedulability, while significantly improving average system safety compared to the existing NMR.

This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in SIGBED Review, VOL.12, ISS.1, http://doi.acm.org/10.1145/2752801.2752808, Over the past decades several approaches for schedu- lability analysis have been proposed for both uniprocessor and multi-processor real-time systems. Although different techniques are employed, very little has been put forward in using formal specifications, with the consequent possibility for misinterpretations or ambiguities in the problem statement. Using a logic based approach to schedulability analysis in the design of hard real-time systems eases the synthesis of correct-by- construction procedures for both static and dynamic verification processes. In this paper we propose a novel approach to schedulability analysis based on a timed temporal logic with time durations. Our approach subsumes classical methods for uniprocessor scheduling analysis over compositional resource models by providing the developer with counter-examples, and by ruling out schedules that cause unsafe violations on the system. We also provide an example showing the effectiveness of our proposal., This work was partially supported by National Funds through FCT (Portuguese Foundation for Science and Technology) and by ERDF (European Regional Development Fund) through COMPETE (Operational Programme ’Thematic Fac- tors of Competitiveness’), within projects Ref. FCOMP-01- 0124-FEDER-022701 (CISTER), FCOMP-01-0124-FEDER- 015006 (VIPCORE) and FCOMP-01-0124-FEDER-020486 (AVIACC).

In hard real-time systems, gain time is defined as the difference between the Worst Case Execution Time (WCET) of a hard task and its actual processor consumption at runtime. This paper presents the results of an empirical study about how the presence of a significant amount of gain time in a hard real-time system questions the advantages of using the most representative scheduling algorithms or policies for aperiodic or soft tasks in fixed-priority preemptive systems. The work presented here refines and complements many other studies in this research area in which such policies have been introduced and compared. This work has been performed by using the authors' testing framework for soft scheduling policies, which produces actual, synthetic, randomly generated applications, executes them in an instrumented Real-Time Operating System (RTOS), and finally processes this information to obtain several statistical outcomes. The results show that, in general, the presence of a significant amount of gain time reduces the performance benefit of the scheduling policies under study when compared to serving the soft tasks in background, which is considered the theoretical worst case. In some cases, this performance benefit is so small that the use of a specific scheduling policy for soft tasks is questionable. © 2012 IEEE., This work is partially funded by research projects PROMETEO/2008/051, CSD2007-022, and TIN2008-04446.

In this paper, we consider offline validation of hard real-time systems composed of both periodic and sporadic tasks, embedded on centralized multi-processor architectures. To model hard real-time systems, we use untimed finite automata: each accepted word is a valid operational behavior of the periodic component of the system. Then, by associating generating functions with edges of the automaton, we give a modular decisional technique to decide the feasibility of sporadic tasks.

We present an approach to static priority preemptive process scheduling for the synthesis of hard real-time distributed embedded systems where communication plays an important role. The communication model is based on a time-triggered protocol. We have developed an analysis for the communication delays proposing four different message scheduling policies over a time-triggered communication channel. Optimization strategies for the synthesis of communication are developed, and the four approaches to message scheduling are compared using extensive experiments.

This paper presents several real-time scheduling algorithms developed to support rapid prototyping of embedded systems using the Computer Aided Prototyping System (CAPS). The CAPS tools are based on the Prototyping System Description Language (PSDL), which is a high-level language designed specifically to support the conceptual modeling of real-time embedded systems. This paper describes the scheduling algorithms used in CAPS along with the associated timing constraint and hardware models, which include single and multi-processor configurations.

Dynamic voltage/frequency scaling (DVFS) is one of the most effective techniques for reducing energy use. In this paper, we focus on the pinwheel task model to develop a variable voltage processor with d discrete voltage/speed levels. Depending on the granularity of execution unit to which voltage scaling is applied, DVFS scheduling can be defined in two categories: (i) inter-task DVFS and (ii) intra-task DVFS. In the periodic pinwheel task model, we modified the definitions of both intra- and inter-task and design their DVFS scheduling to reduce the power consumption of DVFS processors. Many previous approaches have solved DVFS problems by generating a canonical schedule in advance and thus require pseudo polynomial time and space because the length of a canonical schedule depends on the hyperperiod of the task periods and is generally of exponential length. To limit the length of the canonical schedules and predict their task execution, tasks with arbitrary periods are first transformed into harmonic periods and their key features are profiled. The proposed methods have polynomial time and space complexities, and experimental results show that, under identical assumptions, the proposed methods achieve more energy savings than the previous methods.