Initial results on fuzzy floating point computation for multimedia processors

During the recent years, the market of mid/low-end portable systems such as PDAs or mobile digital phones have experimented a revolution in both selling volume and features as handheld devices incorporate Multimedia applications. This fact brings to an increase in the computational demands of the devices, while still having the limitation of power (and energy) consumption. Instruction memoization is a promising technique to help alleviate the problem of power consumption of expensive functional units such as the floating-point one. Unfortunately, this technique could be energy-inefficient for low-end systems due to the additional power consumption of the relatively big tables required. In this paper we present a novel way of understanding multimedia floating point operations based on the fuzzy computation paradigm: losses in the computation precision may exchange performance for negligible errors in the output. Exploiting the implicit characteristics of media FP computation, we propose a new technique called fuzzy memoization. Fuzzy memoization expands the capabilities of classic memoization by attaching entries with similar inputs to the same output. We present a case of study for a SH4 like processor and report good performance and power-delay improvements with feasible hardware requirements.Peer ReviewedPostprint (published version

On the efficiency of reductions in µ-SIMD media extensions

Many important multimedia applications contain a significant fraction of reduction operations. Although, in general, multimedia applications are characterized for having high amounts of Data Level Parallelism, reductions and accumulations are difficult to parallelize and show a poor tolerance to increases in the latency of the instructions. This is specially significant for µ-SIMD extensions such as MMX or AltiVec. To overcome the problem of reductions in µ-SIMD ISAs, designers tend to include more and more complex instructions able to deal with the most common forms of reductions in multimedia. As long as the number of processor pipeline stages grows, the number of cycles needed to execute these multimedia instructions increases with every processor generation, severely compromising performance. The paper presents an in-depth discussion of how reductions/accumulations are performed in current µ-SIMD architectures and evaluates the performance trade-offs for near-future highly aggressive superscalar processors with three different styles of µ-SIMD extensions. We compare a MMX-like alternative to a MDMX-like extension that has packed accumulators to attack the reduction problem, and we also compare it to MOM, a matrix register ISA. We show that while packed accumulators present several advantages, they introduce artificial recurrences that severely degrade performance for processors with high number of registers and long latency operations. On the other hand, the paper demonstrates that longer SIMD media extensions such as MOM can take great advantage of accumulators by exploiting the associative parallelism implicit in reductions.Peer ReviewedPostprint (published version

Fuzzy memoization for floating-point multimedia applications

Instruction memoization is a promising technique to reduce the power consumption and increase the performance of future low-end/mobile multimedia systems. Power and performance efficiency can be improved by reusing instances of an already executed operation. Unfortunately, this technique may not always be worth the effort due to the power consumption and area impact of the tables required to leverage an adequate level of reuse. In this paper, we introduce and evaluate a novel way of understanding multimedia floating-point operations based on the fuzzy computation paradigm: performance and power consumption can be improved at the cost of small precision losses in computation. By exploiting this implicit characteristic of multimedia applications, we propose a new technique called tolerant memoization. This technique expands the capabilities of classic memoization by associating entries with similar inputs to the same output. We evaluate this new technique by measuring the effect of tolerant memoization for floating-point operations in a low-power multimedia processor and discuss the trade-offs between performance and quality of the media outputs. We report energy improvements of 12 percent for a set of key multimedia applications with small LUT of 6 Kbytes, compared to 3 percent obtained using previously proposed techniques.Peer ReviewedPostprint (published version

Three-dimensional memory vectorization for high bandwidth media memory systems

Vector processors have good performance, cost and adaptability when targeting multimedia applications. However, for a significant number of media programs, conventional memory configurations fail to deliver enough memory references per cycle to feed the SIMD functional units. This paper addresses the problem of the memory bandwidth. We propose a novel mechanism suitable for 2-dimensional vector architectures and targeted at providing high effective bandwidth for SIMD memory instructions. The basis of this mechanism is the extension of the scope of vectorization at the memory level, so that 3-dimensional memory patterns can be fetched into a second-level register file. By fetching long blocks of data and by reusing 2-dimensional memory streams at this second-level register file, we obtain a significant increase in the effective memory bandwidth. As side benefits, the new 3-dimensional load instructions provide a high robustness to memory latency and a significant reduction of the cache activity, thus reducing power and energy requirements. At the investment of a 50% more area than a regular SIMD register file, we have measured and average speed-up of 13% and the potential for power savings in the L2 cache of a 30%.Peer ReviewedPostprint (published version

Command vector memory systems: high performance at low cost

The focus of this paper is on designing both a low cost and high performance, high bandwidth vector memory system that takes advantage of modern commodity SDRAM memory chips. To successfully extract the full bandwidth from SDRAM parts, we propose a new memory system organization based on sending commands to the memory system as opposed to sending individual addresses. A command specifies, in a few bytes, a request for multiple independent memory words. A command is similar to a burst found in DRAM memories, but does not require the memory words to be consecutive. The command is sent to all sections of the memory array simultaneously, thus not requiring a crossbar in the proper sense. Our simulations show that this command based memory system can improve performance over a traditional SDRAM-based memory system by factors that range between 1.15 up to 1.54. Moreover, in many cases, the command memory system outperforms even the best SRAM memory system under consideration. Overall the command based memory system achieves similar or better results than a 10 ns SRAM memory system (a) using fewer banks and (b) using memory devices that are between 15 to 60 times cheaper.Peer ReviewedPostprint (published version

Exploiting a new level of DLP in multimedia applications

This paper proposes and evaluates MOM: a novel ISA paradigm targeted at multimedia applications. By fusing conventional vector ISA approaches together with more recent SIMD-like (Single Instruction Multiple Data) ISAs (such as MMX), we have developed a new matrix oriented ISA which efficiently deals with the small matrix structures typically found in multimedia applications. MOM exploits a level of DLP not reachable by neither conventional vector ISAs nor SIMD-like media ISA extensions. Our results show that MOM provides a factor of 1.3x to 4x performance improvement when compared with two different multimedia extensions (MMX and MDMX) on several kernels, which translates into up to a 50% of performance gain when measuring full applications (20% in average). Furthermore, the streaming nature of MOM provides additional advantages for executing multimedia applications, such as a very low fetch pressure or a high tolerance to memory latency, making MOM an ideal candidate for the embedded domain.Peer ReviewedPostprint (published version

Hacia una agricultura multifuncional

Es interesante ubicar las conquistas tecnológicas de estos últimos 20 años dentro de su contexto histórico y social. Resulta curioso que, para algunos la globalización tuviera como hito de inicio la caída del muro de Berlín en el año 1989 hace casi 20 años. Poco tiempo antes, 22 años, España había entrado en un nuevo entorno como el de la Unión Europea. Podemos ver como nuestro medio agrícola a lo largo de estos últimos 20 años se ha encontrado con un mercado más abierto, en libre competencia y en el que la economía -en especial la de la Unión Europea- está orientada hacia el conocimiento y las ideas, es decir hacia la ciencia y la innovación tecnológica

Modelación del proceso de biofiltro percolador para el tratamiento de emisiones en aire de Compuestos Orgánicos Volátiles de elevada solubilidad en agua

La contaminación del aire producida por las emisiones a la atmosfera de compuestos orgánicos volátiles (COV) es una de las causas más importantes asociadas al deterioro de la calidad ambiental. Una de las fuentes principales de emisión de COV son las industrias que utilizan disolventes. En este sentido, las industrias deben hacer un esfuerzo por adaptar sus procesos productivos para minimizar el impacto ambiental. Sin embargo, las propiedades de los disolventes los convierten en indispensables en algunas aplicaciones por lo que el tratamiento de las emisiones derivadas de su uso se convierte en una necesidad. El uso de biofiltros percoladores para la depuración de COV de elevada solubilidad en agua es una tecnología sostenible, habiéndose demostrado que es una alternativa viable técnica y económicamente, tal y como avalan las investigaciones realizadas en las últimas décadas. Sin embargo, el desarrollo de la investigación sobre esta tecnología requiere dar un paso más para lograr consolidarla en el entorno industrial. Este trabajo de tesis doctoral tiene como objetivo principal el de desarrollar una herramienta matemática que incluya los principales mecanismos involucrados en la depuración de aire contaminado con COV de elevada solubilidad en agua mediante el proceso de biofiltro percolador en condiciones de operación típicas de la industria. Los COV de elevada solubilidad en agua están presentes de manera habitual en las emisiones gaseosas procedentes de la industria entre otras, de impresión flexográfica. Pese a que son compuestos con una biodegradabilidad relativamente elevada, la depuración de este tipo de COV suele verse limitada por la disponibilidad de oxígeno en el interior de la biopelícula, lo que favorece la acumulación de contaminante en el interior del sistema. En este sentido, una parte importante de la tesis doctoral ha consistido en profundizar en los mecanismos de transferencia de materia de contaminante y de oxígeno mediante la determinación de los coeficientes de transferencia de materia para ambos compuestos. La herramienta matemática desarrollada en la presente tesis doctoral tiene como finalidad simular y predecir la respuesta transitoria de los biofiltros percoladores sometidos a condiciones de carga variable y riego intermitente. El modelo matemático ha sido aplicado tanto a biofiltros percoladores utilizados en el laboratorio, en condiciones controladas de operación, como a biofiltros percoladores situados en instalaciones industriales, en los que se suele observar patrones de emisión más amortiguados. En la primera etapa de este trabajo se llevó a cabo el estudio experimental a escala de laboratorio de eliminación de emisiones en aire que contenían isopropanol, elegido éste como contaminante modelo. Para ello se utilizaron dos biofiltros percoladores empaquetados con diferente material de relleno: uno desordenado y otro estructurado. Durante este estudio se sometieron a los reactores a condiciones discontinuas de alimentación y de riego intermitente, y se evaluó la respuesta del biofiltro percolador a cambios en la concentración de alimentación de contaminante y de caudal de gas. Los resultados indicaron que el uso de patrones de riego intermitente provocaba una emisión fugitiva de contaminante en la corriente gaseosa de salida del biofiltro percolador que coincidía con el momento del riego. Para evaluar este efecto se aplicaron diferentes condiciones de riego al sistema, concluyendo que el patrón de riego podía utilizarse como estrategia para aumentar el rendimiento del reactor. Así mismo se sometió al reactor a un periodo de 7 semanas sin alimentación de COV. La capacidad de recuperación de los biofiltros percoladores puso de manifiesto la robustez del sistema. La siguiente fase de la tesis se centró en el estudio de la transferencia de materia en los biofiltros percoladores. Para ello se determinaron los coeficientes de transferencia de materia de isopropanol y de oxígeno para diferentes velocidades superficiales de líquido y de gas y para varios materiales de relleno. Los datos obtenidos en este estudio permitieron desarrollar correlaciones empíricas para caracterizar la relación entre los coeficientes de transferencia de materia y las velocidades superficiales de gas y de líquido aplicadas en el biofiltro percolador. Así mismo, se evaluó un material de relleno de uso industrial en términos de transferencia de oxígeno con el objetivo de compararlo con los materiales de relleno empleados en el laboratorio, demostrándose que, en las velocidades de aplicación de los biofiltros percoladores industriales, la transferencia de oxígeno para este material era similar a la obtenida con los materiales utilizados en el laboratorio. En la última parte del presente estudio se desarrolló un modelo matemático para la predicción de la respuesta transitoria de los biofiltros percoladores en condiciones de estado no estacionario de carga y de riego intermitente. El desarrollo del modelo se basó en balances de materia de isopropanol y de oxígeno en la fase gas, en la fase líquida y en la biopelícula. El modelo matemático se desarrolló asumiendo condiciones cíclicas de periodos con riego y de periodos sin riego, ya que ésta es la forma habitual de operación a nivel industrial. Durante los periodos con riego se consideró una fase líquida móvil, mientras que durante los periodos sin riego se consideró una fase líquida estancada. La calibración y validación del modelo matemático se realizó con datos de biofiltros percoladores utilizados a escala de laboratorio y a escala industrial. Las principales hipótesis del modelo estuvieron relacionadas con la resistencia a la transferencia de materia tanto durante el riego (fase líquida móvil) como durante el no riego (fase líquida estancada). La calibración del modelo se llevó a cabo con datos de experimentos realizados a escala de laboratorio en biofiltros percoladores sometidos a riego discontinuo y carga de contaminante intermitente. Considerando despreciable la resistencia a la transferencia de materia producida por la fase líquida estancada durante los periodos sin riego, el modelo fue capaz de reproducir el rendimiento global del sistema así como el patrón de emisiones ocasionado por el riego discontinuo. Además, permitió identificar que la relación entre la concentración de carbono orgánico en el tanque de recirculación y la emisión fugitiva observada durante los periodos con riego estaba asociada al incremento de la resistencia a la transferencia de materia entre la fase gas y la fase líquida móvil con respecto a las determinaciones realizadas en condiciones abióticas. Este fenómeno se asoció al cambio de las propiedades físicas que ocasiona la presencia de biopelícula. La aplicación del modelo para la predicción de las emisiones de salida de un biofiltro percolador instalado en una industria de impresión flexográfica demostró la utilidad práctica del modelo. La aplicación del modelo para la simulación de esta corriente se basó en las hipótesis de la existencia de una resistencia a la transferencia de materia de la fase gas a la fase líquida móvil durante el riego y una resistencia adicional con respecto al biofiltro percolador de laboratorio a la transferencia de materia desde la fase gas a la fase líquida estancada durante los periodos sin riego. Se utilizó un mayor espesor de biopelícula que en los biofiltros percoladores empleados en el laboratorio ya que se identificó que ésta actuaba cíclicamente como fuente/sumidero asociado a los periodos diarios de fabricación/no fabricación. El elevado espesor de la biopelícula provocó que durante los periodos de alimentación de COV al sistema, la parte no degradada del contaminante se acumulara en la biopelícula, produciéndose su desorción en los periodos en los que circulaba aire limpio por el reactor. Todo ello demostró la capacidad del modelo para reproducir los fenómenos complejos involucrados en la respuesta dinámica de los biofiltros percoladores que tratan compuestos orgánicos volátiles de elevada solubilidad en agua. El modelo matemático se integró en una herramienta informática mediante una GUI (Graphical User Inteface) desarrollada con MATLAB®. A fin de facilitar la comunicación con el usuario final, se generaron dos interfaces: una interfaz para introducir los datos para realizar las simulaciones y una interfaz de resultados. La herramienta desarrollada permite introducir de una manera sencilla patrones de concentraciones y caudales de gas variables, así como el uso de patrones de riego intermitente. Al terminar la simulación, la herramienta ofrece una pantalla de resultados con la información más relevante para evaluar el funcionamiento de los biofiltros percoladores: gráficas de patrón de emisión de la concentración de contaminante en la fase gas a la entrada y a la salida del reactor y de la variación temporal de la concentración de carbono disuelto en el tanque de recirculación, así como datos promedio de concentración de contaminante en las emisiones gaseosas a la entrada y a la salida del bioreactor, de carga volumétrica y de capacidad de eliminación.Air pollution produced by the emission to the atmosphere of volatile organic compounds (VOCs) is one of the most important causes associated with deterioration of air quality. One of the main sources of VOC emissions are companies that use solvents. In this regard, they should make an effort to adapt their production processes in order to minimise environmental impact. However, the properties of solvents make them essential in certain applications, so the treatment of derivative emissions becomes a necessity. Use of biotrickling filters for the removal of highly water soluble VOCs is a sustainable technology, having been proven to be technologically and economically a viable alternative, as supported by research in the last few decades. However, research development on this technology requires one further step to achieve consolidation in the industrial environment. The main objective of this dissertation is to develop a mathematical tool that includes the principal mechanisms involved in the removal of VOCs of high solubility in water from air emissions by the biotrickling filtration process in typical industry operating conditions. VOCs of high solubility in water are usually present in gaseous emissions from the flexographic printing industry, among others. Despite being compounds with a relatively high biodegradability, biological removal of such compounds is often limited by oxygen availability within biofilm, which leads to pollutant accumulation within the system. In this regard, an important part of the thesis was focused on the study of the mechanisms of mass transfer of pollutants and oxygen by means of the determination of the mass transfer coefficients for both compounds. The mathematical tool developed here aims to simulate and predict the transient response of the biotrickling filters under variable loading conditions and intermittent spraying. The mathematical model has been applied to biotrickling filters used in the laboratory, under controlled operating conditions, as well as to biotrickling filters located in industrial facilities, in which more buffered emission patterns are observed. The first stage of this work comprises the removal of isopropanol in air emissions at the laboratory scale, selected as a model pollutant. For this purpose, two biotrickling filters filled with different packing materials were used: a random one and a structured one. The reactors were operated under discontinuous loading conditions and intermittent spraying. The response of the biotrickling filter to variations in the inlet concentration of pollutant, as well as in the gas flow, was evaluated. The results showed that intermittent spraying caused a fugitive pollutant emission in the outlet gaseous stream of the biotrickling during spraying. To evaluate this effect, different spraying conditions were tested, concluding that the spray pattern could be used as a strategy to increase the reactor performance. Likewise, a starvation period of seven weeks was applied to both reactors. The resilience of the biotrickling filters showed the robustness of the system. The next stage was focused on the study of mass transfer in biotrickling filters. For this purpose, the mass transfer coefficients of oxygen and of isopropanol were determined. Different superficial gas and liquid velocities as well as different packing materials were tested. Results allowed empirical correlations to be established, which characterised the relationship between the mass transfer coefficients and superficial velocities of liquid and of gas applied to the biotrickling filters. Likewise, a packing material for industrial use was evaluated in terms of oxygen mass transfer, in order to compare it to the packing materials applied in the laboratory. At typical industrial operating conditions, oxygen mass transfer for the industrial material was found to be similar to those obtained for the laboratory packing materials. In the final stage, a mathematical model was developed in order to predict the transient response of the biotrickling filters under non-steady conditions of pollutant loading and of intermittent spray. The model development was based on the mass balances of isopropanol and of oxygen in the gas phase, in the liquid phase and in the biofilm. The mathematical model was built assuming cyclic conditions of spraying/non-spraying periods, the common industrial operational protocol. During spraying periods, a mobile liquid phase was considered, while during non-spraying periods, a stagnant liquid phase was considered. The calibration and validation of the mathematical model was performed using data from biotrickling filters operated at laboratory and industrial scales. The main hypotheses of the model were related to mass transfer resistance during spraying (mobile liquid phase) and mass transfer resistance during non-spraying (stagnant liquid phase). Model calibration was carried out with laboratory biotrickling filters operated under discontinuous spraying and intermittent pollutant loading. By assuming negligible mass transfer resistance for the stagnant liquid phase during non-spraying, the model was able to reproduce the average system performance and the emission pattern occasioned by the discontinuous spraying. In addition, the relationship between VOC concentration in the recirculation tank and the fugitive emission observed during spraying periods was related to higher mass transfer resistance between the gas and the mobile liquid phase during spraying than that obtained during abiotic determinations. This phenomenon was associated with variations in the physical properties caused by the presence of biofilm. The model application for predicting outlet emissions of a biotrickling filter installed in the flexographic printing industrial facility demonstrated its practical usefulness. Model application for simulating this industrial air flow was based on the hypotheses of mass transfer resistance for the mobile liquid phase during spraying and an additional mass transfer resistance from the stagnant liquid phase during non-spraying with respect to laboratory experiments. It was identified that the biofilm acted as a source/sink associated with daily periods of manufacturing/ non-manufacturing. Thus, a greater thickness of biofilm than in the laboratory biotrickling filters was fixed. The thick biofilm caused the accumulation of the non-degraded pollutant during periods with VOCs feeding to the system. The stored pollutant in the biofilm led to desorption during periods when clean air circulated through the reactor. The model capability to reproduce the complex phenomena involved in the dynamic response of the biotrickling filters treating volatile organic compounds with high water solubility was demonstrated. The mathematical model was integrated into an informatics tool using a GUI (Graphical User Interface) developed with MATLAB®. In order to facilitate communication with the end user, two interfaces were generated: an interface to enter data for simulations, and a results interface. The developed tool allows for the introduction of variable patterns of concentration and gas flows in a simple way, and also the use of intermittent spraying patterns. When the simulation ends, the tool offers a results screen with the most relevant information to evaluate the performance of the biotrickling filters: graphic information regarding the pattern of the gaseous emissions at the inlet and at the outlet of the reactor, as well as graphic information regarding the variation of dissolved organic carbon in the recirculation tank. Average data regarding the concentration in the gaseous emission at the inlet and at the outlet of the bioreactor, and the inlet load and the elimination capacity, are also provided

An evaluation of different DLP alternatives for the embedded media domain

The importance of media processing has produced a revolution in the design of embedded processors. In order to face the high computational and technological demands of near future media applications, new embedded processors are including features that were commonly restricted to the general purpose and the supercomputing domains. In this paper we have evaluated the performance of various DLP (Data Level Parallelism) oriented embedded architectures and analyzed quantitative data in order to determine the highlights and disadvantages of each approach. Additionally we have analyzed the differences between the explicit parallel versions of code (often based on the standard algorithms) and the high-tuned, non-vectorizable versions usually found in real multimedia programs. We will show that sub-word SIMD architectures (like MMX) are a very costeffective solution, and that, while long vector architectures provide few improvements at a very high cost, a smart combination between vector and SIMD-like architectures is the alternative that leverages best performance at a reasonable cost. We will also show that the memory latency tolerance, typical of vector architectures, is partially compensated by the worse spatial locality found when executing vector code.Postprint (author's final draft

Computation of the optimal relative pose between overlapping grid maps through discrepancy minimization

Grid maps are a common environment representation in mobile robotics. Many Simultaneous Localization and Mapping (SLAM) solutions divide the global map into submaps, forming some kind of graph or tree to represent the structure of the environment, while the metric details are captured in the submaps. This work presents a novel algorithm that is able to compute a physically feasible relative pose between two overlapping grid maps. Our algorithm can be used for correspondence search (data association), but also for integrating negative information in a unified way. This paper proposes a discrepancy measure between two overlapping grid maps and its application in a quasi Newton optimization algorithm, with the hypothesis that minimizing such discrepancy could provide useful information for SLAM. Experimental evidence is provided showing the high potential of the algorithm