## Fachbereich Elektrotechnik und Informationstechnik

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- Doctoral Thesis (43) (remove)

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- New Solving Techniques for Property Checking of Arithmetic Data Paths (2012)
- The increasing complexity of modern SoC designs makes tasks of SoC formal verification a lot more complex and challenging. This motivates the research community to develop more robust approaches that enable efficient formal verification for such designs. It is a common scenario to apply a correctness by integration strategy while a SoC design is being verified. This strategy assumes formal verification to be implemented in two major steps. First of all, each module of a SoC is considered and verified separately from the other blocks of the system. At the second step – when the functional correctness is successfully proved for every individual module – the communicational behavior has to be verified between all the modules of the SoC. In industrial applications, SAT/SMT-based interval property checking(IPC) has become widely adopted for SoC verification. Using IPC approaches, a verification engineer is able to afford solving a wide range of important verification problems and proving functional correctness of diverse complex components in a modern SoC design. However, there exist critical parts of a design where formal methods often lack their robustness. State-of-the-art property checkers fail in proving correctness for a data path of an industrial central processing unit (CPU). In particular, arithmetic circuits of a realistic size (32 bits or 64 bits) – especially implementing multiplication algorithms – are well-known examples when SAT/SMT-based formal verification may reach its capacity very fast. In cases like this, formal verification is replaced with simulation-based approaches in practice. Simulation is a good methodology that may assure a high rate of discovered bugs hidden in a SoC design. However, in contrast to formal methods, a simulation-based technique cannot guarantee the absence of errors in a design. Thus, simulation may still miss some so-called corner-case bugs in the design. This may potentially lead to additional and very expensive costs in terms of time, effort, and investments spent for redesigns, refabrications, and reshipments of new chips. The work of this thesis concentrates on studying and developing robust algorithms for solving hard arithmetic decision problems. Such decision problems often originate from a task of RTL property checking for data-path designs. Proving properties of those designs can efficiently be performed by solving SMT decision problems formulated with the quantifier-free logic over fixed-sized bit vectors (QF-BV). This thesis, firstly, proposes an effective algebraic approach based on a Gröbner basis theory that allows to efficiently decide arithmetic problems. Secondly, for the case of custom-designed components, this thesis describes a sophisticated modeling technique which is required to restore all the necessary arithmetic description from these components. Further, this thesis, also, explains how methods from computer algebra and the modeling techniques can be integrated into a common SMT solver. Finally, a new QF-BV SMT solver is introduced.

- Model-Based Cross-Design for Wireless Networked Control Systems (2013)
- This work shall provide a foundation for the cross-design of wireless networked control systems with limited resources. A cross-design methodology is devised, which includes principles for the modeling, analysis, design, and realization of low cost but high performance and intelligent wireless networked control systems. To this end, a framework is developed in which control algorithms and communication protocols are jointly designed, implemented, and optimized taking into consideration the limited communication, computing, memory, and energy resources of the low performance, low power, and low cost wireless nodes used. A special focus of the proposed methodology is on the prediction and minimization of the total energy consumption of the wireless network (i.e. maximization of the lifetime of wireless nodes) under control performance constraints (e.g. stability and robustness) in dynamic environments with uncertainty in resource availability, through the joint (offline/online) adaptation of communication protocol parameters and control algorithm parameters according to the traffic and channel conditions. Appropriate optimization approaches that exploit the structure of the optimization problems to be solved (e.g. linearity, affinity, convexity) and which are based on Linear Matrix Inequalities (LMIs), Dynamic Programming (DP), and Genetic Algorithms (GAs) are investigated. The proposed cross-design approach is evaluated on a testbed consisting of a real lab plant equipped with wireless nodes. Obtained results show the advantages of the proposed cross-design approach compared to standard approaches which are less flexible.

- Thermal Modeling and Management of Multi-Core Processors (2014)
- The work presented in this thesis discusses the thermal and power management of multi-core processors (MCPs) with both two dimensional (2D) package and there dimensional (3D) package chips. The power and thermal management/balancing is of increasing concern and is a technological challenge to the MCP development and will be a main performance bottleneck for the development of MCPs. This thesis develops optimal thermal and power management policies for MCPs. The system thermal behavior for both 2D package and 3D package chips is analyzed and mathematical models are developed. Thereafter, the optimal thermal and power management methods are introduced. Nowadays, the chips are generally packed in 2D technique, which means that there is only one layer of dies in the chip. The chip thermal behavior can be described by a 3D heat conduction partial differential equation (PDE). As the target is to balance the thermal behavior and power consumption among the cores, a group of one dimensional (1D) PDEs, which is derived from the developed 3D PDE heat conduction equation, is proposed to describe the thermal behavior of each core. Therefore, the thermal behavior of the MCP is described by a group of 1D PDEs. An optimal controller is designed to manage the power consumption and balance the temperature among the cores based on the proposed 1D model. 3D package is an advanced package technology, which contains at least 2 layers of dies stacked in one chip. Different from 2D package, the cooling system should be installed among the layers to reduce the internal temperature of the chip. In this thesis, the micro-channel liquid cooling system is considered, and the heat transfer character of the micro-channel is analyzed and modeled as an ordinary differential equation (ODE). The dies are discretized to blocks based on the chip layout with each block modeled as a thermal resistance and capacitance (R-C) circuit. Thereafter, the micro-channels are discretized. The thermal behavior of the whole system is modeled as an ODE system. The micro-channel liquid velocity is set according to the workload and the temperature of the dies. Under each velocity, the system can be described as a linear ODE model system and the whole system is a switched linear system. An H-infinity observer is designed to estimate the states. The model predictive control (MPC) method is employed to design the thermal and power management/balancing controller for each submodel. The models and controllers developed in this thesis are verified by simulation experiments via MATLAB. The IBM cell 8 cores processor and water micro-channel cooling system developed by IBM Research in collaboration with EPFL and ETHZ are employed as the experiment objects.