05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Efficient fault tolerance for selected scientific computing algorithms on heterogeneous and approximate computer architectures(2018) Schöll, Alexander; Wunderlich, Hans-Joachim (Prof. Dr.)Scientific computing and simulation technology play an essential role to solve central challenges in science and engineering. The high computational power of heterogeneous computer architectures allows to accelerate applications in these domains, which are often dominated by compute-intensive mathematical tasks. Scientific, economic and political decision processes increasingly rely on such applications and therefore induce a strong demand to compute correct and trustworthy results. However, the continued semiconductor technology scaling increasingly imposes serious threats to the reliability and efficiency of upcoming devices. Different reliability threats can cause crashes or erroneous results without indication. Software-based fault tolerance techniques can protect algorithmic tasks by adding appropriate operations to detect and correct errors at runtime. Major challenges are induced by the runtime overhead of such operations and by rounding errors in floating-point arithmetic that can cause false positives. The end of Dennard scaling induces central challenges to further increase the compute efficiency between semiconductor technology generations. Approximate computing exploits the inherent error resilience of different applications to achieve efficiency gains with respect to, for instance, power, energy, and execution times. However, scientific applications often induce strict accuracy requirements which require careful utilization of approximation techniques. This thesis provides fault tolerance and approximate computing methods that enable the reliable and efficient execution of linear algebra operations and Conjugate Gradient solvers using heterogeneous and approximate computer architectures. The presented fault tolerance techniques detect and correct errors at runtime with low runtime overhead and high error coverage. At the same time, these fault tolerance techniques are exploited to enable the execution of the Conjugate Gradient solvers on approximate hardware by monitoring the underlying error resilience while adjusting the approximation error accordingly. Besides, parameter evaluation and estimation methods are presented that determine the computational efficiency of application executions on approximate hardware. An extensive experimental evaluation shows the efficiency and efficacy of the presented methods with respect to the runtime overhead to detect and correct errors, the error coverage as well as the achieved energy reduction in executing the Conjugate Gradient solvers on approximate hardware.Item Open Access Fault emulation for reconfigurable scan networks(2018) Schwachhofer, DenisAt around their standardization by the IEEE the interest on Reconfigurable Scan Networks (RSNs) by research and industry sparked. The testing of RSNs also raises new challenges. To analyze and cope with these challenges researchers are required to perform fault simulation. And the industry incorporated RSNs into their designs and need to test them to which also requires fault simulation. But the runtime of it is significantly high due to the RSNs’ structure. This thesis introduces a platform for fault emulation of RSNs and analyzes its feasibility. The speedup compared to fault simulation is presented and advantages, limitations and possible optimizations are evaluated and discussed.Item Open Access Modeling of a multi-core microblaze system at RTL and TLM abstraction levels in systemC(2013) Eissa, KarimTransaction Level Modeling (TLM) has recently become a popular approach for modeling contemporary Systems-on-Chip (SoCs) on a higher abstraction level than Register Transfer Level (RTL). In this thesis a multi-core system based on the Xilinx MicroBlaze micro-processor is modeled at RTL and TLM abstraction levels in SystemC. Both implemented models have cycle accurate timing, and are verified against the reference VHDL model using a VHDL / SystemC mixed-language simulation with ModelSim. Finally, performance measurements are carried out to evaluate simulation speedup at the transaction level. Modeling of the MicroBlaze processor is based on a MicroBlaze Instruction Set Simulator (ISS) from SoCLib. A wrapper is therefore implemented to provide communication interfaces between the processor and the rest of the system, as well as control the timing of the ISS operation to reach cycle accurate models. Furthermore, a local memory module based on Block Random Access Memories (BRAMs) is modeled to simulate a complete system consisting of a processor and a local memory.Item Open Access Test planning for low-power built-in self test(2014) Zoellin, Christian G.; Wunderlich, Hans-Joachim (Prof. Dr. rer. nat. habil.)Power consumption has become the most important issue in the design of integrated circuits. The power consumption during manufacturing or in-system test of a circuit can significantly exceed the power consumption during functional operation. The excessive power can lead to false test fails or can result in the permanent degradation or destruction of the device under test. Both effects can significantly impact the cost of manufacturing integrated circuits. This work targets power consumption during Built-In Self-Test (BIST). BIST is a Design-for-Test (DfT) technique that adds additional circuitry to a design such that it can be tested at-speed with very little external stimulus. Test planning is the process of computing configurations of the BIST-based tests that optimize the power consumption within the constraints of test time and fault coverage. In this work, a test planning approach is presented that targets the Self-Test Using Multiple-input signature register and Parallel Shift-register sequence generator (STUMPS) DfT architecture. For this purpose, the STUMPS architecture is extended by clock gating in order to leverage the benefits of test planning. The clock of every chain of scan flip-flops can be independently disabled, reducing the switching activity of the flip-flops and their clock distribution to zero as well as reducing the switching activity of the down-stream logic. Further improvements are obtained by clustering the flip-flops of the circuit appropriately. The test planning problem is mapped to a set covering problem. The constraints for the set covering are extracted from fault simulation and the circuit structure such that any valid cover will test every targeted fault at least once. Divide-and-conquer is employed to reduce the computational complexity of optimization against a power consumption metric. The approach can be combined with any fault model and in this work, stuck-at and transition faults are considered. The approach effectively reduces the test power without increasing the test time or reducing the fault coverage. It has proven effective with academic benchmark circuits, several industrial benchmarks and the Synergistic Processing Element (SPE) of the Cell/B.E.™ Processor (Riley et al., 2005). Hardware experiments have been conducted based on the manufacturing BIST of the Cell/B.E.™ Processor and shown the viability of the approach for industrial, high-volume, high-end designs. In order to improve the fault coverage for delay faults, high-frequency circuits are sometimes tested with complex clock sequences that generate test with three or more at-speed cycles (rather than just two of traditional at-speed testing). In order to allow such complex clock sequences to be supported, the test planning presented here has been extended by a circuit graph based approach for determining equivalent combinational circuits for the sequential logic. In addition, this work proposes a method based on dynamic frequency scaling of the shift clock that utilizes a given power envelope to it full extent. This way, the test time can be reduced significantly, in particular if high test coverage is targeted.Item Open Access Efficient modeling and computation methods for robust AMS system design(2018) Gil, Leandro; Radetzki, Martin (Prof. Dr.-Ing.)This dissertation copes with the challenge regarding the development of model based design tools that better support the mixed analog and digital parts design of embedded systems. It focuses on the conception of efficient modeling and simulation methods that adequately support emerging system level design methodologies. Starting with a deep analysis of the design activities, many weak points of today’s system level design tools were captured. After considering the modeling and simulation of power electronic circuits for designing low energy embedded systems, a novel signal model that efficiently captures the dynamic behavior of analog and digital circuits is proposed and utilized for the development of computation methods that enable the fast and accurate system level simulation of AMS systems. In order to support a stepwise system design refinement which is based on the essential system properties, behavior computation methods for linear and nonlinear analog circuits based on the novel signal model are presented and compared regarding the performance, accuracy and stability with existing numerical and analytical methods for circuit simulation. The novel signal model in combination with the method proposed to efficiently cope with the interaction of analog and digital circuits as well as the new method for digital circuit simulation are the key contributions of this dissertation because they allow the concurrent state and event based simulation of analog and digital circuits. Using a synchronous data flow model of computation for scheduling the execution of the analog and digital model parts, very fast AMS system simulations are carried out. As the best behavior abstraction for analog and digital circuits may be selected without the need of changing component interfaces, the implementation, validation and verification of AMS systems take advantage of the novel mixed signal representation. Changes on the modeling abstraction level do not affect the experiment setup. The second part of this work deals with the robust design of AMS systems and its verification. After defining a mixed sensitivity based robustness evaluation index for AMS control systems, a general robust design method leading to optimal controller tuning is presented. To avoid over-conservative AMS system designs, the proposed robust design optimization method considers parametric uncertainty and nonlinear model characteristics. The system properties in the frequency domain needed to evaluate the system robustness during parameter optimization are obtained from the proposed signal model. Further advantages of the presented signal model for the computation of control system performance evaluation indexes in the time domain are also investigated in combination with range arithmetic. A novel approach for capturing parameter correlations in range arithmetic based circuit behavior computation is proposed as a step towards a holistic modeling method for the robust design of AMS systems. The several modeling and computation methods proposed to improve the support of design methodologies and tools for AMS system are validated and evaluated in the course of this dissertation considering many aspects of the modeling, simulation, design and verification of a low power embedded system implementing Adaptive Voltage and Frequency Scaling (AVFS) for energy saving.Item Open Access Item Open Access Development of an error detection and recovery technique for a SPARC V8 processor in FPGA technology(2011) Boktor, AndrewField-Programmable Gate Arrays (FPGAs) found widespread use in many areas of applications, including safety and mission-critical systems. More and more manufacturers are choosing to implement designs on FPGAs. However, SRAM-based FPGAs are proven to be much more prone to Single Event Upsets (SEUs) compared to traditional Application-Specific Integrated Circuit (ASIC) designs. Moreover, SEU affects FPGAs in more severe ways compared to ASIC. Techniques to provide fault-tolerance for SRAM-based FPGAs become essential to maintain their advantages over other technologies. This thesis presents a fault-tolerance technique for pipeline architectures in FPGA technology. It provides fault-tolerance against SEUs in the design and is able to detect faults in the FPGA configuration. It also proposes an additional mechanism that detects all SEUs independent of their location. Pipeline operation can be resumed with known techniques of partial reconfiguration. Both designs occupy a much smaller area compared to known techniques such as TMR in combination with Scrubbing. They introduce no additional time penalty in case of fault-free operation. Fault injection and simulation were used to validate the design and calculate the fault coverage.Item Open Access Software-basierter Selbsttest eingebetteter Speicher(2015) Ebinger, FelixProzessoren werden häufig mittels softwarebasierter Selbsttests (SBST) getestet, da dieses Testverfahren mehrere Vorteile besitzt. Zunächst ist der Test zerstörungsfrei, und wird im funktionalen Betriebszustand des Prozessors durchgeführt. Es ist weder eine Veränderung des Hardwaredesigns erforderlich noch ist ein Übertesten möglich. Die Testmethode ist flexibel einsetzbar und kann sowohl beim Herstellungstest als auch im Feld genutzt werden. Speicher werden dagegen üblicherweise mittels eingebauter Selbsttests (engl. built-in self-test, BIST) getestet, da der Overhead durch die zusätzliche Testhardware nur gering ausfällt und diese Tests bei Speichern ohne Performance-Einbußen realisiert werden können. In dieser Arbeit wird die softwarebasierte Umsetzung von Speichertests untersucht um die Vorteile softwarebasierter Selbsttests auch bei Speichertests nutzen zu können. Dies stellt eine Herausforderung dar, da softwarebasiert nicht jede Operationsfolge mit frei wählbarem Zeitverhalten erzeugt werden kann. Insbesondere bei dynamischen Fehlern kann dies zu einer Verringerung der Testabdeckung führen. Hierzu wird ein Framework zur automatischen Umwandlung von Marchtestbeschreibungen in Testprogramme für den miniMIPS-Prozessor vorgestellt. Dabei steht besonders die Laufzeit des Testprogramms und die erreichte Testabdeckung im Vordergrund. Die Testabdeckung wird durch Simulation und Fehlerinjektion experimentell bestimmt. Es zeigt sich, dass die Fehlerabdeckung für die untersuchten statische und dynamische Fehlermodelle durch die vorgestellte Implementierung in Software nicht beeinträchtigt wird.Item Open Access Online self-test wrapper for runtime-reconfigurable systems(2013) Wang, JilingReconfigurable Systems-on-a-Chip (SoC) architectures consist of microprocessors and Field Programmable Gate Arrays (FPGAs). In order to implement runtime reconfigurable systems, these SoC devices combine the ease of programmability and the flexibility that FPGAs provide. One representative of these is the new Xilinx Zynq-7000 Extensible Processing Platform (EPP), which integrates a dual-core ARM Cortex-A9 based Processing System (PS) and Programmable Logic (PL) in a single device. After power on, the PS is booted and the PL can subsequently be configured and reconfigured by the PS. Recent FPGA technologies incorporate the dynamic Partial Reconfiguration (PR) feature. PR allows new functionality to be programmed online into specific regions of the FPGA while the performance and functionality of the remaining logic is preserved. This on-the-fly reconfiguration characteristic enables designers to time-multiplex portions of hardware dynamically, load functions into the FPGA on an as-needed basis. The configuration access port on the FPGA can be used to load the configuration data from memory to the reconfigurable block, which enables the user to reconfigure the FPGA online and test runtime systems. Manufactured in the advanced 28 nm technologies, the modern generations of FPGAs are increasingly prone to latent defects and aging-related failure mechanisms. To detect faults contained in the reconfigurable gate arrays, dedicated on and off-line test methods can be employed to test the device in the field. Adaptive systems require that the fault is detected and localized, so that the faulty logic unit will not be used in future reconfiguration steps. This thesis presents the development and evaluation of a self-test wrapper for the reconfigurable parts in such hybrid SoCs. It comprises the implementation of Test Configurations (TCs) of reconfigurable components as well as the generation and application of appropriate test stimuli and response analysis. The self-test wrapper is successfully implemented and is fully compatible with the AMBA protocols. The TC implementation is based on an existing Java framework for Xilinx Virtex-5 FPGA, and extended to the Zynq-7000 EPP family. These TCs are successfully redesigned to have a full logic coverage of FPGA structures. Furthermore, the array-based testing method is adopted and the tests can be applied to any part of the reconfigurable fabric. A complete software project has been developed and built to allow the reconfiguration process to be triggered by the ARM microprocessor. Functional test of the reconfigurable architecture, online self-test execution and retrieval of results are under the control of the embedded processor. Implementation results and analysis demonstrate that TCs are successfully synthesized and can be dynamically reconfigured into the area under test, and subsequent tests can be performed accordingly.Item Open Access Effiziente mehrwertige Logiksimulation verzögerungsbehafteter Schaltungen auf datenparallelen Architekturen(2012) Schöll, AlexanderDie Validierung von Schaltungsentwürfen nimmt bis zu 70 Prozent der Entwurfsdauer von hochintegrierten Schaltungen in Anspruch. Validierungsaufgaben wie Fehlersimulationen, Alterungsanalysen, Untersuchungen zum Energieverbrauch, Testmengencharakterisierungen sowie die Bewertung der Zuverlässigkeit erfordern hochperformante verzögerungsbehaftete Logiksimulationen. Die Verzögerungen innerhalb hochintegrierter Schaltungen sind von Variationen geprägt. Die Berücksichtigung von Variationen innerhalb der Validierungsaufgaben erhöht den Aufwand nochmals erheblich. In der vorliegenden Arbeit wird die Simulationsumgebung CWTSim vorgestellt, welche die Anforderungen der Validierungsaufgaben erfüllt. CWTSim verfolgt den Ansatz einer kontinuierlichen Simulation von Stimulifolgen auf Gatterebene, wodurch eine Simulation von potentiell unbegrenzten Stimulifolgen ermöglicht wird. CWTSim ist fähig, verschiedene Simulationsinstanzen parallel zu simulieren, in denen Variationen des Verzögerungsverhaltens abgebildet wurden. Hierzu wurde CWTSim parallelisiert und auf eine datenparallele Architektur abgebildet. Die benötigte Zeit, welche zur Simulation einer Vielzahl von Verzögerungsvariationen aufgewendet werden muss, wird durch CWTSim signifikant reduziert. CWTSim erreicht Beschleunigungen bis zu 168x im Vergleich zur sequentiellen Auswertung mit einem kommerziellen Simulationswerkzeug.