On the Determinism of Multi-core Processors

Hard real time systems are evolving in order to respond to the increasing demand in complex functionalities while taking advantage of newer hardware. Software development for safety critical systems has to comply with strict requirements that will facilitate the certification process. During this process, each part of the system is evaluated, requiring a certain level of assurance in order to provide confidence in the product. In particular there must be a level of confidence that the system behaves deterministically that may be based on functionality, resources and time. The success of system verification depends greatly on the capacity to determine its exact behavior. Nonetheless, hardware evolved in order to maximize the average computation power throughput with little to no regard to the deterministic aspect. Therefore modern architectural features of processors, like pipelines, cache memories and co-processors, make it hard to verify that all the needed properties are respected. The multi-core is furthermore difficult to analyze as the architecture employs mechanisms that compromise strong spatial and temporal partitioning when using shared resources without rigorous access control like shared caches or shared input/outputs. In this paper we identify and analyze the main sources of nondeterminism of the multi-cores with regard to the timing estimation. Precise determination of the worst case execution time is a challenging task even in single-core architectures. The problems are accentuated in the multi-core context mainly due to the resource sharing that can lead to highly complex interactions or to nondeterminism. Most of the units that generate behaviors that are hard to take into account can be deactivated, but it is not always easy to predict the impact on the performance. Nevertheless some of the features cannot be disabled (such as the out of order execution or some nondeterministic crossbar access policies) which leads to the invalidation of the respective platform for applications with high criticality level. We will address the problematic units, propose configuration or architecture guidelines and estimate their impact on the performance and determinism of the system

Détermination des pire-temps d’exécution (WCET) pour des plateformes embarquées par analyse statique

Nowadays real-time systems are omnipresent and embedded systems thrive in a variety of application fields. When they are integrated into safety-critical systems, the verification of their properties becomes a crucial part. Dependability is a primary design goal in environments that use hard real-time systems, whereas general-use microprocessors were designed with a high performance goal. The average-throughput maximization design choice is intrinsically opposed to design goals such as dependability that benefit mostly from highly deterministic architectures without local optimizations. Besides the growth in complexity of the embedded systems, platforms are getting more and more heterogeneous. With regard to the respect of the timing constraints, real-time systems are classified in two categories: hard real-time systems (the non respect of a deadline can lead to catastrophic consequences) and soft real-time systems (missing a deadline can cause performance degradation and material loss). We analyze hard real-time systems that need precise and safe determination of the worst-case execution time bounds in order to be certified.The validation of their non-functional properties is a complex and resource consuming task. One of the main reasons is that currently available solutions focus on delivering precise estimations through tools that are highly dependent on the underlying platform (in order to provide precise and safe results, the architecture of the system must be taken into account).In this thesis we address the above issues by introducing a timing analysis method that maintains a good level of precision while being applicable to a variety of platforms. This adaptability is achieved through separating as much as possible the worst-case execution time (WCET) estimation from the model of the hardware. Our approach consists in the introduction of a new formal modeling language that captures the complex behaviour of modern hardware and is guided by the timing analysis in order to achieve the needed precision to scalability tradeoff. The analysis drives a conjoint symbolic execution of the program's binary and the processor model using a dynamic prediction module that decides what states to merge in order to limit the state space explosion. Several state merging algorithms are introduced and applied that can also give an estimation of the introduced precision loss.La détermination précise de pires temps d’exécution (WCET) est un sujet de grand intérêt pour les systèmes embarqués critiques. Le sujet de la Thèse adresse des problèmes qui ne sont pas résolus dans la littérature notamment l’inertie notable dans le changement de plateformes cibles des analyseurs existants et la perte de précision lors du passage à l’échelle. Nos travaux se concentrent justement sur une souplesse au changement du processeur à analyser et la maitrise de la perte de précision à l’aide d’un nouvel langage de modélisation du matériel qui se trouve en étroit lien avec l’analyseur même.Une estimation sûre du WCET nécessite la prise en compte du matériel sur lequel le programme est exécuté. Les processeurs embarqués dans les systèmes critiques présentent des composants qui ont été conçus non pas pour faciliter leur analyse mais pour maximiser les performances moyennes, introduisant une variabilité temporelle significative. Le temps d'exécution est donc dépendent, entre autres des valeurs effectives de données mais aussi de l'historique d'exécution. Le but étant d'estimer le pire temps d'exécution, l'option de supposer qu'à chaque fois l'optimisation ne se produit pas et que le pire temps possible est nécessaire conduit à une surestimation trop importante. A ce problème se rajoute aussi le fait que nous ne pouvons pas supposer qu'un pire temps local (par exemple le nombre de cycles pendant une micro-opération du pipeline) contribuera au vrai pire temps global à cause des anomalies temporelles des processeurs. Tous les chemins d'exécution, engendrés par la totalité des entrées possibles doivent donc être analysés. Le fait de devoir gérer cette explosion combinatoire, nous a guidé dans les choix de conception du modèle utilisé pour simuler le processeur. Nous avons conçu une méthode de spécification et d'analyse de systèmes, basée sur la méthode des abstract state machines (ASM). L'extension HiTAsm consiste en l'incorporation des notions de hiérarchie et de temporalité, pour pouvoir gérer l'explosion combinatoire en choisissant une définition d'un composant parmi plusieurs niveaux d'abstraction possibles et pour pouvoir estimer le temps écoulé entre chaque transition des états du système. Cela permet l'estimation de la consommation temporelle et la variation dynamique du niveau d'abstraction du système analysé, afin d'analyser un grand nombre d'états, tout en minimisant la perte de précision. Le modèle du processeur et l'analyseur sont complètement séparés, ce qui est nécessaire pour rendre l'outil adaptable aux changements de plateforme. L'analyseur est basé sur une exécution symbolique conjointe du binaire et du modèle de processeur spécifié avec HiTAsm. En partant des valeurs symboliques, toutes les entrées possibles du binaire sont analysées, en utilisant des sur-approximations uniquement quand c'est nécessaire de manière à minimiser la perte de précision et fournir le pire-temps d’exécution du programme le plus proche de la valeur théorique

Polymer Translocation through Nanometer Pores

In this paper the loaded polymer transport and its escape via a nanometer size aperture, virtually by nanomembrane, the polymer being moved by an exterior electrostatic field, has been studied. Assuming a linear dependency of the friction coefficient on the number of segments m and a parabolic behavior for the open-free (Gibbs) energy, in attendance of a present electrical potential across nanopore, an explicit flux formula for the polymers passed over a dimensional restricted pore, was derived. In addition, the linear polymers transport through a nanometer-sized pore under the action of a constant force is presented. The important mechanical effects of superimposed steady force and the monomers number of macromolecule chain on the polymer translocation process by nanomembranes, in a 2D diffusion model, have been demonstrated. The escape time by a three-dimensional graph as a function of the electric field intensity and monomers number of polymer was represented

Electrical Signal Modeling in Cochlear Implants. Study of Temperature and Humidity Effects

The present paper discusses the climatic effects of humidity and temperature on cochlear implant functioning and the quality of the electrical sound signal. MATLAB Simulink simulations were prepared, offering insights into signal behavior under such climatic parameter changes. A simulation setup of the cochlear implant was developed, where a source type selection was used to change between a voice recording and a "chirp" sound. In addition, a DC blocking filter was applied to the input signal. A simulation code, with the application of the climatic influence via the air attenuation function, was developed. Thereby, the attenuation of temperature and humidity in the sound atmospheric circulation of the input signal, at T = 0 degrees C and RH = 0% and at T = 36 degrees C and RH = 40% was graphically represented. The results of the electrical pulse generator for each of the eight channels, with the IIR filter, Gaussian noise, temperature variation, humidity influence, and control of denoise block activity, were thus obtained

Time Estimation of Polymer Translocation through Nano-Membrane

In this paper, the charged polymer escapement phenomenon, via a little hole of nano-metric dimensions arranged in a constitutive biological membrane, is studied. We will present the case of the transport process of an ideal polymer in a 3-dimensional extended region separated by a fine boundary named membrane in a free energy barrier attendance. Additionally, the general translocation time formula, respectively, the transition time from the cis area to the trans area, is presented. The model for estimation of the likelihood, designated by P(x, t), as a macromolecular chain of lengthiness equal to x, to be able to pass by the nanopore in escape period t, was optimized. The longest-lasting likely escape time found with this model is indicated to be tp = 330 μs. Thus, the results obtained with the described formula are in good agreement with those announced in the specialized literature

Spatial Series and Fractal Analysis Associated with Fracture Behaviour of UO₂ Ceramic Material

SEM micrographs of the fracture surface for UO2 ceramic materials have been analysed. In this paper, we introduce some algorithms and develop a computer application based on the time-series method. Utilizing the embedding technique of phase space, the attractor is reconstructed. The fractal dimension, lacunarity, and autocorrelation dimension average value have been calculated

Fractal Modeling of Polymer Plasma Laser Ablation, Plasma Plume Tsallis Entropy and Its q-Statistics Interpretation, Part I: Theory

Polymer plasma produced by laser ablation is investigated in a theoretical manner. In relation to the fact that the charge carrier circulation is assumed to take place on fractal curves, the so-called fractality type, electrical charge transport can be resolved by an extended scale relativity method. In addition, an elegant mathematical model, utilizing a conjecture of fractal space-time, is elaborated. The complete solution and its graphical representation for temperature distribution in two-dimensional and three-dimensional cases are successfully introduced. The discrete physical behavior and irrevocable transformation of nanoscale microdomain substructures by laser ablation are realistically examined. Further, benefiting from the interpretation of the fractal analysis, each of the experimental results can be fairly explained. On top of that, this paper presents a proof of Tsallis nonextensive q-statistics, especially for the plasma plume studied. Tsallis entropy in direct connection with fractal dynamics and chaotic-type mechanics of the plasma plume and time-series representation of plasma temperature is introduced for the first time in the present publication, and the q-statistics of the plume plasma temperature are also studied, among others

A Multifractal Vision of 5-Fluorouracil Release from Chitosan-Based Matrix

A suite of four drug deliverance formulations grounded on 5-fluorouracil enclosed in a chitosan-founded intercellular substance was produced by 3,7-dimethyl-2,6-octadienal with in situ hydrogelation. The formulations have been examined from a morphological and structural point of view by Fourier transform infrared (FTIR) spectroscopy and microscopy with polarized light, respectively. The polarized optical microscopy (POM) pictures of the three representative formulations obtained were investigated by fractal analysis. The fractal dimension and lacunarity of each of them were thus calculated. In this paper, a novel theoretical method for mathematically describing medicament deliverance dynamics in the context of the polymeric medicament constitution limit has been advanced. Assuming that the polymeric drug motion unfolds only on the so-called non-differentiable curves (considered mathematically multifractal curves), it looks like in a one-dimensional hydrodynamic movement within a multifractal formalism, the drug-release physics models are provided by isochronous kinetics, but at a scale of resolution necessarily non-differentiable

Fractal Analysis and Time Series Application in ZY-4 SEM Micro Fractographies Evaluation

SEM microfractographies of Zircaloy-4 are studied by fractal analysis and the time-series method. We first develop a computer application that associates the fractal dimension and lacunarity to each SEM micrograph picture, and produce a nonlinear analysis of the data acquired from the quantitatively evaluated time series. Utilizing the phase space-embedding technique to reconstruct the attractor and to compute the autocorrelation dimension, the fracture surface of the Zircaloy-4 samples is investigated. The fractal analysis method manages to highlight damage complications and provide a description of morphological parameters of various fractures by calculating the fractal dimension and lacunarity

Fractal Analysis and Time Series Application in ZY-4 SEM Micro Fractographies Evaluation

SEM microfractographies of Zircaloy-4 are studied by fractal analysis and the time-series method. We first develop a computer application that associates the fractal dimension and lacunarity to each SEM micrograph picture, and produce a nonlinear analysis of the data acquired from the quantitatively evaluated time series. Utilizing the phase space-embedding technique to reconstruct the attractor and to compute the autocorrelation dimension, the fracture surface of the Zircaloy-4 samples is investigated. The fractal analysis method manages to highlight damage complications and provide a description of morphological parameters of various fractures by calculating the fractal dimension and lacunarity