Elementary operations: a novel concept for source-level timing estimation

Early application timing estimation is essential in decision making during design space exploration of heterogeneous embedded systems in terms of hardware platform dimensioning and component selection. The decisions which have the impact on project duration and cost must be made before a platform prototype is available and software code is ready to be linked and thus timing estimation must be done using high-level models and simulators. Because of the ever increasing need to shorten the time to market, reducing the amount of time required to obtain the results is as important as achieving high estimation accuracy. In this paper, we propose a novel approach to source-level timing estimation with the aim to close the speed-accuracy gap by raising the level of abstraction and improving result reusability. We introduce a concept – elementary operations as distinct parts of source code which enable capturing platform behaviour without having the exact model of the processor pipeline, cache etc. We also present a timing estimation method which relies on elementary operations to craft hardware profiling benchmark and to build application and platform profiles. Experiments show an average estimation error of 5%, with maximum below 16%

Learning-based system-level power modeling of hardware IPs

Accurate power models for hardware components at high levels of abstraction are a critical component to enable system-level power analysis and optimization. Virtual platform prototypes are widely utilized to support early system-level design space exploration. There is, however, a lack of accurate and fast power models of hardware components at such high-levels of abstraction. In this dissertation, we present novel learning‑based approaches for extending fast functional simulation models of white-, gray-, and black-box custom hardware intellectual property components (IPs) with accurate power estimates. Depending on the observability, we extend high-level functional models with the capability to capture data-dependent resource, block, or I/O activity without a significant loss in simulation speed. We further leverage state-of-the-art machine learning techniques to synthesize abstract power models that can predict cycle-, block-, and invocation-level power from low-level hardware implementations, where we introduce novel structural decomposition techniques to reduce model complexities and increase estimation accuracy. Our white-box approach integrates with existing high-level synthesis (HLS) tools to automatically extract resource mapping information, which is used to trace data-dependent resource-level activity and drive a cycle-accurate online power-performance model during functional simulation. Our gray-box approach supports power estimation at coarser basic block granularity. It uses only limited information about block inputs and outputs to extract light-weight block-level activity from a functional simulation and drive a basic block-level power model that utilizes a control flow decomposition to improve accuracy and speed. It is faster than cycle-level models, while providing a finer granularity than invocation-level models, which allows to further navigate accuracy and speed trade-offs. We finally propose a novel approach for extending behavioral models of black-box hardware IPs with an invocation-level power estimate. Our black-box model only uses input and output history to track data-dependent pipeline behavior, where we introduce a specialized ensemble learning that is composed out of individually selected cycle-by-cycle models with reduced complexity and increased accuracy. The proposed approaches are fully automated by integrating with existing, commercial HLS tools for custom hardware synthesized by HLS. Results of applying our approaches to various industrial‑strength design examples show that our power models can predict cycle‑, basic block-, and invocation-level power consumption to within 10%, 9%, and 3% of a commercial gate-level power estimation tool, respectively, all while running at several order of magnitude faster speeds of 1-10Mcycles/sec.Electrical and Computer Engineerin

Spintronic terahertz emitters based on ferro- and ferrimagnetic thin film systems

Elektromagnetische Strahlung im Terahertzfrequenzbereich von 0.1 bis 30 THz bietet zahlreiche Anwendungsmöglichkeiten, beispielsweise in Spektroskopie- und Bildgebungsverfahren, sowohl im Bereich der Grundlagenforschung, als auch für industrielle Prozesse. Da der Terahertzspektralbereich jedoch zwischen den mit etablierten elektronischen und optischen Emittern gut zugänglichen Mikrowellen- und Infrarotspektralbereichen liegt, sind Emittersysteme immer noch teuer und limitiert in Bezug auf Leistung und Bandbreite. Ein neues vielversprechendes Konzept für die Terahertzerzeugung stellen die sogenannten spintronischen Emittersysteme dar. Diese bestehen aus Multilagensystemen ferromagnetischer (FM) und nichtmagnetischer (NM) Metallschichten mit Schichtdicken im Bereich weniger Nanometer. Die Anregung einer FM/NM-Bilage mit einem femtosekundenlangen optischen Laserpuls führt zur Ausbildung eines spinpolarisierten Ladungsstromes Js von der FM in die NM Schicht, der auf der Anregung spinpolarisierter Elektronen der FM Schicht über das Ferminiveau beruht. In der NM Schicht wird Js auf Grund des inversen Spin-Hall-Effekts in einen transversalen Ladungsstrompuls Jc konvertiert, der zur Emission elektromagnetischer Strahlung im Terahertzfrequenzbereich führt. Die Abstrahlcharakteristik der Emitter kann durch Variation der verwendeten Materialien, Schichtdicken, oder durch die Verwendung komplexerer Multilagensysteme optimiert werden. Die vorliegende Arbeit präsentiert Studien zu spintronischen Terahertzemittersystemen basierend auf verschiedenen magnetischen dünnen Filmen kombiniert mit Pt und W Schichten. Die Abhandlung kann in zwei Teilbereiche untergliedert werden. Das Ziel der ersten drei Studien war die Untersuchung des Einflusses der magnetischen Eigenschaften unterschiedlicher FM und insbesondere auch ferrimagnetischer (FI) Legierungsschichten auf die Terahertzemission. Hierfür wurden Bilagensysteme bestehend aus NM Pt Schichten in Kombination mit FM CoFe, sowie FI TbFe und GdFe Legierungsschichten mit variierendem Eisengehalt (0 ≤ x ≤ 1) hergestellt. Die laserangeregte Terahertzemission wurde in Abhängigkeit des angelegten Magnetfelds, der Fluenz des Anregungslasers und der Temperatur gemessen. Die Ergebnisse wurden unter Einbeziehung detaillierter Untersuchungen der strukturellen, magnetischen, elektrischen und optischen Eigenschaften der Proben erklärt. Der zweite Teilbereich der Arbeit befasst sich mit der Entwicklung komplexerer Multilagenterahertzemittersysteme, welche das Schalten der Amplitude zwischen Zuständen hoher und niedriger Terahertzemission ermöglichen und zudem Potential für eine Steigerung der Terahertzamplitude bieten. Hierfür wurde, basierend auf den Terahertzemissioncharakteristiken des zuvor untersuchten FI Pt/GdFe Systems, ein Emitter entwickelt, der das Schalten der Terahertzamplitude durch Veränderung der Temperatur ermöglicht. In einer weiteren Studie wurde zudem die Anwendung eines Spin-Valve-Systems als magnetisch schaltbares Emittersystem demonstriert. Dieses ermöglicht ein reversibles Schalten der Emissionsamplitude mit kleinen angelegten magnetischen Feldern in der Größenordnung weniger Millitesla.Electromagnetic radiation in the terahertz (THz) frequency range from 0.1 to 30 THz can be highly useful for spectroscopy and imaging experiments in fundamental scientific research as well as for industrial applications. However, as THz regime bridges the gap between electronic and optical frequencies, emitter systems are still expensive and limited in power and bandwidth. A novel approach to overcome these challenges is given by the so-called spintronic terahertz emitters, which are based on ferromagnetic (FM) and non-magnetic metal (NM) layers with thicknesses of a few nanometers. Excitation of a FM/NM bilayer with a femtosecond optical laser pump pulse leads to the formation of an ultrafast spin current Js from the FM toward the NM layer, which is caused by the excitation of spin-polarized electrons of the FM layer above the Fermi level. In the NM layer, Js is converted into a transverse charge current pulse Jc due to the inverse spin Hall effect, which leads to the emission of electromagnetic radiation in the THz frequency regime. The emission properties of the emitters can be optimized by utilizing different materials, layer thicknesses, or more complex multilayer structures. The present work shows studies of spintronic THz emitter systems that are based on different magnetic thin films combined with Pt and W layers. The experimental studies can be divided into two parts. The main goal of the first part was to investigate how the magnetic properties of different FM and in particular also ferrimagnetic (FI) materials are reflected in the THz emission properties of a spintronic emitter system. Therefore, thin bilayers consisting of FM CoFe, or FI TbFe or GdFe alloy thin films with varying Fe content (0 ≤ x ≤ 1), combined with Pt layers have been prepared. The laser-excited spintronic THz emission has been investigated in dependence on the applied magnetic field, the temperature, and the pump fluence of the excitation laser. The results have been explained with regard to detailed characterizations of the structural, magnetic, electrical, and optical properties of the samples. The second goal of this work was set on the development of more functional multilayer emitter systems that allow for the control of the THz emission amplitude between a high- and a low-amplitude state and also might open the way for higher THz emission amplitudes. Based on the results of the previously investigated FI Pt/GdFe bilayer emitter system, a new concept of a THz emitter that can be switched by a temperature change from a high- to a low-amplitude state has been developed. Additionally, the use of a spin-valve system as a spintronic emitter system that allows for the switching of the emission amplitude by small applied magnetic fields in the range of a few millitesla has been demonstrated