A constant-time dynamic storage allocator for real-time systems

Dynamic memory allocation has been used for decades. However, it has seldom been used in real-time systems since the worst case of spatial and temporal requirements for allocation and deallocation operations is either unbounded or bounded but with a very large bound. In this paper, a new allocator called TLSF (Two Level Segregated Fit) is presented. TLSF is designed and implemented to accommodate real-time constraints. The proposed allocator exhibits time-bounded behaviour, O(1), and maintains a very good execution time. This paper describes in detail the data structures and functions provided by TLSF. We also compare TLSF with a representative set of allocators regarding their temporal cost and fragmentation. Although the paper is mainly focused on timing analysis, a brief study and comparative analysis of fragmentation incurred by the allocators has been also included in order to provide a global view of the behaviour of the allocators. The temporal and spatial results showed that TLSF is also a fast allocator and produces a fragmentation close to that caused by the best existing allocators.

A Task Model to Reduce Control Delays

Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, these two phases have been developed in separate ways. Recently, some works have pointed out the necessity of the integration of the control design and its implementation. One of these works reduce the delay variance of control tasks (defined as the control action interval (CAI) and data acquisition interval (DAI) parameters) splitting every task into three parts. The CAI reduction method highly reduces the delay variance and improves the control performance. This work shows how to evaluate these delays under static and dynamic scheduling policies. A new task model is proposed in order to reduce the CAI and DAI parameters, which implies an improvement in the control performance. The new task model will be implemented in a real process, and the experimental measurements will show how, effectively, the control performance is highly improved with the methods presented in this paper.     

New recovery error indicator for adaptive finite-element analysis on waveguiding structures

The adaptive finite-element method (FEM) is an iterative variant of the FEM where, in a first step, an initial mesh with few and low-order elements is generated, the corresponding algebraic problem is solved and the error in the solution is estimated in order to add degrees of freedom in those regions of the domain with the biggest error estimation. This process is repeated until an ending condition is reached. The two basic stages in this method are the error indication and the mesh enrichment. In this paper, within the analysis of waveguiding structures, a new error indicator based on the curl recovery is described. In addition, an overview on refinement techniques is presented, and the h-refinement employed in this study is briefly described. Results obtained with the curl-recovery indicator are discussed and compared with the classical nonadaptive FEM and two previously developed error indicators: the residual and flux continuity indicators.     

Schedulability analysis of dynamic priority real-time systems with contention

The Journal of Supercomputing - In multicore scheduling of hard real-time systems, there is a significant source of unpredictability due to the interference caused by the sharing of hardware...     

Susceptibility analysis of arbitrarily shaped 2-D slotted screensusing a hybrid generalized scattering matrix finite-element technique

The electromagnetic susceptibility (EMS) inside slotted screens has been studied using a hybrid technique. The screen is characterized by a generalized admittance or impedance matrix, computed using the finite element method (FEM), which is then combined with a modal solution in free-space. The scattering matrix for the screen can then be easily computed. As a practical application, the electrical performance of a slotted square envelope has been studied. In general, it is shown that coupling to the interior of slotted screens is maximized at frequencies corresponding to resonances of the shorted screen, provided that the fields do not vanish near the aperture     

Analysis of general lossy inhomogeneous and anisotropic waveguidesby the finite-element method (FEM) using edge elements

Several finite element formulations based on edge elements have been developed in recent years, avoiding the appearance of spurious modes in waveguides. However, no formulation of this kind dealing with general lossy inhomogeneous and anisotropic waveguides has been found in the literature. In this paper, a new finite element scheme for the most general linear waveguides has been derived from vector wave equations via a Galerkin procedure. In this formulation, triangular and quadrilateral edge elements have been used in order to avoid the spurious solutions. Furthermore, the final eigensystem involves only very sparse matrices, thus allowing important savings in time and memory     

Assessment of Complex Radiated EMC Problems Involving Slotted Enclosures Using a 2-D Generalized Circuital Approach

A 2D version of the generalized circuital analysis (GCA) has been used along with the finite element method (FEM) to estimate both the radiated perturbation produced by an arbitrary current distribution (represented by a set of linear current sources) covered by a slotted enclosure, and the field coupled to a slotted screen due to a radiated perturbation. The effect of a given enclosure is modeled by means of a scattering matrix (which depends only on its geometry) obtained by the FEM. On the other hand, any arbitrary perturbating field can be expanded in a series of cylindrical harmonics, and then, the total field is computed everywhere using the scattering matrices. This method has the advantage over conventional FEM approaches that FEM is applied only once, and then a wide range of electromagnetic compatibility (EMC) problems can be solved with almost no extra computational effort. Two-dimensional models of relevant EMC problems involving both emission and immunity have been studied in order to extract useful information for actual 3D systems. In spite of the 2D approach, very interesting conclusions can be derived from the examples presented in this paper (like the effect of slot resonances in the field distribution within slotted enclosures or the coupling between two connected cavities).     

Microwave disinfestation of bulk timber.

In this paper a complete microwave system for bulk timber disinfestation is developed and tested. A commercial FEM simulator has been used to design the applicator, looking for structures providing uniform field distributions, which is a factor of capital relevance for a successful treatment. Special attention has also been given to the reduction of electromagnetic energy leakage. A dual polarized cylindrical applicator with a corrugated flange has been designed. The applicator has also been numerically tested emulating some real-life operating conditions. A prototype has been built using two low-cost magnetrons of 900 W and high power coaxial cables and it has been tested inside a shielded semianechoic chamber. The tests have been carried out in three stages: validation of the applicator design, determination of the lethal dosage as a function of the insect position and the maximum wood temperature allowed and statement of safe operation procedures.     

Analysis of window-constrained execution time systems

Feasibility tests for hard real-time systems provide information about the schedulability of the task set. However, this information is a yes or a no answer, that is, whether the task set achieves the test or not. From the real-time system design point of view, having more information available would be useful. For example, how much the computation time can vary without jeopardising the system feasibility. This work specifically provides methods to determine off-line how much a task can increase its computation time, by maintaining the system feasibility under a dynamic priority scheduling. The extra time can be determined not only in all the task activations, but in n of a window of m invocations. This is what we call a window-constrained execution time system. The results presented in this work can be used in all kinds of real-time systems: fault tolerance management, imprecise computation, overrun handling, control applications, etc. Patricia Balbastre is an assistant professor of Computer Engineering. She graduated in Electronic Engineering at the Technical University of Valencia, Spain, in 1998. And the Ph.D. degree in Computer Science at the same university in 2002. Her main research interests include real-time operating systems, dynamic scheduling algorithms and real-time control. Ismael Ripoll received the B.S. degree from the Polytechnic University of Valencia, Spain, in 1992; the Ph.D. degree in Computer Science at the Polytechnic University of Valencia, Spain, in 1996. Currently he is Professor in the DISCA Department of the same University. His research interests include embedded and real-time operating systems. Alfons Crespo is Professor of the Department of Computer Engineering of the Technical University of Valencia. He received the PhD in Computer Science from the Technical University of Valencia, Spain, in 1984. He held the position of Associate professor in 1986 and full Professor in 1991. He leads the group of Industrial Informatics and has been the responsible of several European and Spanish research projects. His main research interest include different aspects of the real-time systems (scheduling, hardware support, scheduling and control integration, …). He has published more than 60 papers in specialised journals and conferences in the area of real-time systems.