The MFIBVP real-time multiplier

This paper presents the architecture of the MFIBVP real-time multiplier which is The MFIBVP technique is a combination of the MSB–First computation, the Interval-Bounded Arithmetic and the Variable-Precision computation techniques.The MFIBVP computation guarantees the computation carried out will produce high accuracy from the early computation time, self error estimation and time-optimal computation. This paper shows the performance of the MFIBVP real-time multiplier unit that can gives accuracy of it’s intermediate-result more than 99% since the second phase of its process

Design of Energy-efficient Hierarchical Scheduling for Integrated Modular Avionics Systems

AbstractRecently the integrated modular avionics (IMA) architecture which introduces the concept of resource partitions becomes popular as an alternative to the traditional federated architecture. This study investigates the problem of designing hierarchical scheduling for IMA systems. The proposed scheduler model enables strong temporal partitioning, so that multiple hard real-time applications can be easily integrated into an uniprocessor platform. This paper derives the mathematic relationships among partition cycle, partition capacity and schedulability under the real-time condition, and then proposes an algorithm for optimizing partition parameters. Real-time tasks with arbitrary deadlines are considered for generality. To further improve the basic algorithm and reduce the energy consumption for embedded systems in aircraft, a power optimization approach is also proposed by exploiting the slack time. Experimental results show that the designed system can guarantee the hard real-time requirement and reduce the power consumption by at least 14%

Trusted Collaborative Real Time Scheduling in a Smart Card Exokernel

This paper presents the work we have conducted concerning real time scheduling in Camille, an exokernel dedicated to smart cards. We show that it is possible to embedded a flexible real-time operating system despite the important hardware limitations of the smart card platform. We present the major difficulties one has to face when integrating real time support in an exokernel embedded on a very resource-limited platform. We first present a naive solution consisting in allocating an equal time slice to every system extensions and letting each one share it as needed amongst its tasks. We show that this solution does not account for loading of new extensions in the system, and that it can fail if some extensions have much more work to carry out than the others. We then present a more complex solution based upon collaborative schedulers grouped as virtual extensions. We show that this solution supports dynamic loading of new extensions and works even for very unbalanced task repartitions. We finally address the issue of trust between the collaborating extensions and we propose a solution based on exhaustive testing and formal proving of the plan functions

MSB-First Interval-Bounded Variable-Precision RealTime Arithmetic Unit

This paper presents a paradigm of real-time processing on the lowest level of computing systems: the arithmetic unit. The arithmetic unit based on this principle containing addition, subtraction, multiplication and division operations is  described.  The  development  of  the  computation  model  is  based  on  the  Soft Computing and the Imprecise Computation paradigms, combined with the MSBFirst  and  the  Interval  Arithmetic  techniques.  Those  paradigms  and  techniques give  the  arithmetic  unit  design  the  ability  to  compute  with  precisions  as  a function  of time available or accuracy needed. The predictability of processing time and result's accuracy are obtained by means of processing granularity of k bits and by  using look-up tables. We present an evaluation of  the operation in time  delay  and  computation  accuracy  that  shows  significant  performance improvement over conventional arithmetic unit architecture, that is,  the ability to produce  intermediate-result  during  execution  time,  to  give  certainty  in computation  accuracy  even  before  the  process  finish  time  by  providing  two intermediate-results,  which  act  as  the  lower  and  upper  bound  of  the  real  and complete computation result, and finally, gain high computation accuracy from the early time of the execution process

Virtual Node - To Achieve Temporal Isolation and Predictable Integration of Real-Time Components

We present an approach of two-level deployment process for component models used in distributed real-time embedded systems to achieve predictable integration of real-time components. Our main emphasis is on the new concept of virtual node with the use of a hierarchical scheduling technique. Virtual nodes are used as means to achieve predictable integration of software components with real-time requirements. The hierarchical scheduling framework is used to achieve temporal isolation between components (or sets of components). Our approach permits detailed analysis, e.g., with respect to timing, of virtual nodes and this analysis is also reusable with the reuse of virtual nodes. Hence virtual node preserves real-time properties across reuse and integration in different contexts

Capacity sharing and stealing in serverbased real-time systems

A dynamic scheduler that supports the coexistence of guaranteed and non-guaranteed bandwidth servers is proposed. Overloads are handled by an efficient reclaiming of residual capacities originated by early completions as well as by allowing reserved capacity stealing of non-guaranteed bandwidth servers. The proposed dynamic budget accounting mechanism ensures that at a particular time the currently executing server is using a residual capacity, its own capacity or is stealing some reserved capacity, eliminating the need of additional server states or unbounded queues. The server to which the budget accounting is going to be performed is dynamically determined at the time instant when a capacity is needed. This paper describes and evaluates the proposed scheduling algorithm, showing that it can efficiently reduce the mean tardiness of periodic jobs. The achieved results become even more significant when tasks’ computation times have a large variance

Hierarchical Scheduling for Real-Time Periodic Tasks in Symmetric Multiprocessing

In this paper, we present a new hierarchical scheduling framework for periodic tasks in symmetric multiprocessor (SMP) platforms. Partitioned and global scheduling are the two main approaches used by SMP based systems where global scheduling is recommended for overall performance and partitioned scheduling is recommended for hard real-time performance. Our approach combines both the global and partitioned approaches of traditional SMP-based schedulers to provide hard real-time performance guarantees for critical tasks and improved response times for soft real-time tasks. Implemented as part of VxWorks, the results are confirmed using a real-time benchmark application, where response times were improved for soft real-time tasks while still providing hard real-time performance

Periodic Resource Model for Compositional Real-Time Guarantees

We address the problem of providing compositional hard real-time guarantees in a hierarchy of schedulers. We first propose a resource model to characterize a periodic resource allocation and present exact schedulability conditions for our proposed resource model under the EDF and RM algorithms. Using the exact schedulability conditions, we then provide methods to abstract the timing requirements that a set of periodic tasks demands under the EDF and RM algorithms as a single periodic task. With these abstraction methods, for a hierarchy of schedulers, we introduce a composition method that derives the timing requirements of a parent scheduler from the timing requirements of its child schedulers in a compositional manner such that the timing requirement of the parent scheduler is satisfied, if and only if, the timing requirements of its child schedulers are satisfied

Real-time hierarchical systems with arbitrary scheduling at global level

[EN] Partitioned architectures isolate software components into independent partitions whose execution will not interfere with other partitions, preserving temporal and spatial isolation. Hierarchical scheduling can effectively be used to schedule these systems. Schedulability analysis of hierarchical real-time systems is based on prior knowledge of the local and the global scheduling algorithms. In a partitioned system with safety and security issues and certification assurance levels, global scheduling is usually generated using a static table. Therefore, each partition must allocate task jobs only in the temporal windows reserved for that partition. Even if the static table can come originally from a periodic server or other scheduling policy, the final plan may be modified due to changes in the system requirements. As a consequence, the CPU assignment to a partition does not have to correspond to any known policy. In this case, it is not possible to use existing scheduling analysis for hierarchical systems. This paper studies a new scheduling problem: a hierarchical system in which global policy is not known but provided as a set of arbitrary time windows.This work has been funded by the Spanish government under grant TIN2014-56158-C4-1-P-AR and by the European Commission under FP7-ICT-2013.3.4 Programme with grant 610640Guasque Ortega, A.; Balbastre, P.; Crespo, A. (2016). Real-time hierarchical systems with arbitrary scheduling at global level. Journal of Systems and Software. 119:70-86. https://doi.org/10.1016/j.jss.2016.05.040S708611

Seamless composition and integration: a perspective on formal methods research

Formal methods are now a central component of computer-science education and research. However, there will always be advances in mathematical logic -- a.k.a. `formal methods' among computer scientists -- leading to advances in reliable, safe and secure computing. There are many research directions that will promote the impact of formal methods on computer science in significant and novel ways. We outline two directions, each associated with its own research challenges, that are complementary to the current state-of-the-art: one of composability and one of integration, each considered in a specific context drawn from our own recent research and teaching experience. We try to clarify why the study and ultimate resolution of these two challenges hold the promise of important breakthroughs in the accessability of formal methods and, ultimately, their applicability.National Science Foundation (CCF-0820138