Harmonic scheduling of linear recurrences in digital filter design

Linear difference equations involving recurrences are fundamental equations that describe many important signal processing applications. For many high sample rate digital filter applications, we need to effectively parallelize the linear difference equations used to describe digital filters - a difficult task due to the recurrences inherent in the data dependences. We present a novel approach, Harmonic Scheduling, that exploits parallelism in these recurrences beyond loop-carried dependencies, and which generates optimal schedules for parallel evaluation of linear difference equations with resource constraints. This approach also enables us to derive a parallel schedule with minimum control overhead, given an execution time with resource constraints. We also present a Harmonic Scheduling algorithm that generates optimal schedules for digital filters described by second-order difference equations with resource constraints

Loop transformations for clustered VLIW architectures

With increasing demands for performance by embedded systems, especially by digital signal processing (DSP) applications, embedded processors must increase available instructionlevel parallelism (ILP) within significant constraints on power consumption and chip cost. Unfortunately, supporting a large amount of ILP on a processor while maintaining a single register file increases chip cost and potentially decreases overall performance due to increased cycle time. To address this problem, some modern embedded processors partition the register file into multiple low-ported register files, each directly connected with one or more functional units. These functional unit/register file groups are called clusters. Clustered VLIW (very long instruction word) architectures need extra copy operations or delays to transfer values among clusters. To take advantage of clustered architectures, the compiler must expose parallelism for maximal functional-unit utilization, and schedule instructions to reduce intercluster communication overhead. High-level loop transformations offer an excellent opportunity to enhance the abilities of low-level optimizers to generate code for clustered architectures. This dissertation investigates the effects of three loop transformations, i.e., loop fusion, loop unrolling, and unroll-and-jam, on clustered VLIW architectures. The objective is to achieve high performance with low communication overhead. This dissertation discusses the following techniques: Loop Fusion This research examines the impact of loop fusion on clustered architectures. A metric based upon communication costs for guiding loop fusion is developed and tested on DSP benchmarks. Unroll-and-jam and Loop Unrolling A new method that integrates a communication cost model with an integer-optimization problem is developed to determine unroll amounts for loop unrolling and unroll-and-jam automatically for a specific loop on a specific architecture. These techniques have been implemented and tested using DSP benchmarks on simulated, clustered VLIW architectures and a real clustered, embedded processor, the TI TMS320C64X. The results show that the new techniques achieve an average speedup of 1.72-1.89 on five different clustered architectures. These techniques have been implemented and tested using DSP benchmarks on simulated, clustered VLIW architectures and a real clustered, embedded processor, the TI TMS320C64X. The results show that the new techniques achieve an average speedup of 1.72-1.89 on five different clustered architectures

Articles indexats publicats per investigadors del Campus de Terrassa: 2013

Aquest informe recull els 228 treballs publicats per 177 investigadors/es del Campus de Terrassa en revistes indexades al Journal Citation Report durant el 2013Preprin

Percolation-based compiling for evaluation of parallelism and hardware design trade-offs

This thesis investigates parallelism and hardware design trade-offs of parallel and pipelined architectures. To explore these trade-offs we developed a retargetable compiler based on a set of powerful code transformations called Percolation Scheduling (PS) that map programs with real-time constraints and/or massive time requirements onto synchronous, parallel, high-performance or semi-custom architectures.High-performance is achieved through extraction of application inherent fine-grain parallelism and the use of a suitable architecture. Exploiting fine-grain parallelism is a critical part of exploiting all of the parallelism available in a given program, particularly since highly irregular forms of parallelism are often not visible at coarser levels and since the use of low-level parallelism has a multiplicative effect on the overall performance.To extract substantial parallelism from both the hardware and the compiler, we use a clean, highly parallel VLIW-like architecture that is synchronous, has multiple functional units and has a single program counter. The use of a hazard-free and homogeneous architecture does not result only in a better VLSI design but also considerably increases the compiler's ability to produce better code. To further enhance parallelism we modified the uni-cycle VLIW model and extended the transformations such that pipelined units that provide extra parallelism are used.Another approach presented is of resource constrained scheduling (RCS). Since the RCS problem is known to be NP-hard, in practice it may be solved only by a heuristic approach. We argue that using the heuristic after extraction of the unlimited-resources schedule may yield better results than if the heuristic has been applied at the beginning of the scheduling process.Through a series of benchmarks we evaluate hardware design trade-offs and show that speed-ups on average of one order of magnitude are feasible with sufficient functional units. However, when resources are limited we show that the number of functional units needed may be optimized for a particular suite of application programs

Algorithmic Compositional Methods and their Role in Genesis: A Multi-Functional Real-Time Computer Music System

Algorithmic procedures have been applied in computer music systems to generate compositional products using conventional musical formalism, extensions of such musical formalism and extra-musical disciplines such as mathematical models. This research investigates the applicability of such algorithmic methodologies for real-time musical composition, culminating in Genesis, a multi-functional real-time computer music system written for Mac OS X in the SuperCollider object-oriented programming language, and contained in the accompanying DVD. Through an extensive graphical user interface, Genesis offers musicians the opportunity to explore the application of the sonic features of real-time sound-objects to designated generative processes via different models of interaction such as unsupervised musical composition by Genesis and networked control of external Genesis instances. As a result of the applied interactive, generative and analytical methods, Genesis forms a unique compositional process, with a compositional product that reflects the character of its interactions between the sonic features of real-time sound-objects and its selected algorithmic procedures. Within this thesis, the technologies involved in algorithmic methodologies used for compositional processes, and the concepts that define their constructs are described, with consequent detailing of their selection and application in Genesis, with audio examples of algorithmic compositional methods demonstrated on the accompanying DVD. To demonstrate the real-time compositional abilities of Genesis, free explorations with instrumentalists, along with studio recordings of the compositional processes available in Genesis are presented in audiovisual examples contained in the accompanying DVD. The evaluation of the Genesis system’s capability to form a real-time compositional process, thereby maintaining real-time interaction between the sonic features of real-time sound objects and its selected algorithmic compositional methods, focuses on existing evaluation techniques founded in HCI and the qualitative issues such evaluation methods present. In terms of the compositional products generated by Genesis, the challenges in quantifying and qualifying its compositional outputs are identified, demonstrating the intricacies of assessing generative methods of compositional processes, and their impact on a resulting compositional product. The thesis concludes by considering further advances and applications of Genesis, and inviting further dissemination of the Genesis system and promotion of research into evaluative methods of generative techniques, with the hope that this may provide additional insight into the relative success of products generated by real-time algorithmic compositional processes

Radiomics for Response Assessment after Stereotactic Radiotherapy for Lung Cancer

Stereotactic ablative radiotherapy (SABR) is a guideline-specified treatment option for patients with early stage non-small cell lung cancer. After treatment, patients are followed up regularly with computed tomography (CT) imaging to determine treatment response. However, benign radiographic changes to the lung known as radiation-induced lung injury (RILI) frequently occur. Due to the large doses delivered with SABR, these changes can mimic the appearance of a recurring tumour and confound response assessment. The objective of this work was to evaluate the accuracy of radiomics, for prediction of eventual local recurrence based on CT images acquired within 6 months of treatment. A semi-automatic decision support system was developed to segment and sample regions of common post-SABR changes, extract radiomic features and classify images as local recurrence or benign injury. Physician ability to detect timely local recurrence was also measured on CT imaging, and compared with that of the radiomics tool. Within 6 months post-SABR, physicians assessed the majority of images as no recurrence and had an overall lower accuracy compared to the radiomics system. These results suggest that radiomics can detect early changes associated with local recurrence that are not typically considered by physicians. These appearances detected by radiomics may be early indicators of the promotion and progression to local recurrence. This has the potential to lead to a clinically useful computer-aided decision support tool based on routinely acquired CT imaging, which could lead to earlier salvage opportunities for patients with recurrence and fewer invasive investigations of patients with only benign injury

Proceedings of the 7th Sound and Music Computing Conference

Proceedings of the SMC2010 - 7th Sound and Music Computing Conference, July 21st - July 24th 2010

Control techniques for mechatronic assisted surgery

The treatment response for traumatic head injured patients can be improved by using an autonomous robotic system to perform basic, time-critical emergency neurosurgery, reducing costs and saving lives. In this thesis, a concept for a neurosurgical robotic system is proposed to perform three specific emergency neurosurgical procedures; they are the placement of an intracranial pressure monitor, external ventricular drainage, and the evacuation of chronic subdural haematoma. The control methods for this system are investigated following a curiosity led approach. Individual problems are interpreted in the widest sense and solutions posed that are general in nature. Three main contributions result from this approach: 1) a clinical evidence based review of surgical robotics and a methodology to assist in their evaluation, 2) a new controller for soft-grasping of objects, and 3) new propositions and theorems for chatter suppression sliding mode controllers. These contributions directly assist in the design of the control system of the neurosurgical robot and, more broadly, impact other areas outside the narrow con nes of the target application. A methodology for applied research in surgical robotics is proposed. The methodology sets out a hierarchy of criteria consisting of three tiers, with the most important being the bottom tier and the least being the top tier. It is argued that a robotic system must adhere to these criteria in order to achieve acceptability. Recent commercial systems are reviewed against these criteria, and are found to conform up to at least the bottom and intermediate tiers. However, the lack of conformity to the criteria in the top tier, combined with the inability to conclusively prove increased clinical benefit, particularly symptomatic benefit, is shown to be hampering the potential of surgical robotics in gaining wide establishment. A control scheme for soft-grasping objects is presented. Grasping a soft or fragile object requires the use of minimum contact force to prevent damage or deformation. Without precise knowledge of object parameters, real-time feedback control must be used to regulate the contact force and prevent slip. Moreover, the controller must be designed to have good performance characteristics to rapidly modulate the fingertip contact force in response to a slip event. A fuzzy sliding mode controller combined with a disturbance observer is proposed for contact force control and slip prevention. The robustness of the controller is evaluated through both simulation and experiment. The control scheme was found to be effective and robust to parameter uncertainty. When tested on a real system, however, chattering phenomena, well known to sliding mode research, was induced by the unmodelled suboptimal components of the system (filtering, backlash, and time delays). This reduced the controller performance. The problem of chattering and potential solutions are explored. Real systems using sliding mode controllers, such as the control scheme for soft-grasping, have a tendency to chatter at high frequencies. This is caused by the sliding mode controller interacting with un-modelled parasitic dynamics at the actuator-input and sensor-output of the plant. As a result, new chatter-suppression sliding mode controllers have been developed, which introduce new parameters into the system. However, the effect any particular choice of parameters has on system performance is unclear, and this can make tuning the parameters to meet a set of performance criteria di cult. In this thesis, common chatter-suppression sliding mode control strategies are surveyed and simple design and estimation methods are proposed. The estimation methods predict convergence, chattering amplitude, settling time, and maximum output bounds (overshoot) using harmonic linearizations and invariant ellipsoid sets