Towards an embedded board-level tester: study of a configurable test processor

The demand for electronic systems with more features, higher performance, and less power consumption increases continuously. This is a real challenge for design and test engineers because they have to deal with electronic systems with ever-increasing complexity maintaining production and test costs low and meeting critical time to market deadlines. For a test engineer working at the board-level, this means that manufacturing defects must be detected as soon as possible and at a low cost. However, the use of classical test techniques for testing modern printed circuit boards is not sufficient, and in the worst case these techniques cannot be used at all. This is mainly due to modern packaging technologies, a high device density, and high operation frequencies of modern printed circuit boards. This leads to very long test times, low fault coverage, and high test costs. This dissertation addresses these issues and proposes an FPGA-based test approach for printed circuit boards. The concept is based on a configurable test processor that is temporarily implemented in the on-board FPGA and provides the corresponding mechanisms to communicate to external test equipment and co-processors implemented in the FPGA. This embedded test approach provides the flexibility to implement test functions either in the external test equipment or in the FPGA. In this manner, tests are executed at-speed increasing the fault coverage, test times are reduced, and the test system can be adapted automatically to the properties of the FPGA and devices located on the board. An essential part of the FPGA-based test approach deals with the development of a test processor. In this dissertation the required properties of the processor are discussed, and it is shown that the adaptation to the specific test scenario plays a very important role for the optimization. For this purpose, the test processor is equipped with configuration parameters at the instruction set architecture and microarchitecture level. Additionally, an automatic generation process for the test system and for the computation of some of the processor’s configuration parameters is proposed. The automatic generation process uses as input a model known as the device under test model (DUT-M). In order to evaluate the entire FPGA-based test approach and the viability of a processor for testing printed circuit boards, the developed test system is used to test interconnections to two different devices: a static random memory (SRAM) and a liquid crystal display (LCD). Experiments were conducted in order to determine the resource utilization of the processor and FPGA-based test system and to measure test time when different test functions are implemented in the external test equipment or the FPGA. It has been shown that the introduced approach is suitable to test printed circuit boards and that the test processor represents a realistic alternative for testing at board-level.Der Bedarf an elektronischen Systemen mit zusätzlichen Merkmalen, höherer Leistung und geringerem Energieverbrauch nimmt ständig zu. Dies stellt eine erhebliche Herausforderung für Entwicklungs- und Testingenieure dar, weil sie sich mit elektronischen Systemen mit einer steigenden Komplexität zu befassen haben. Außerdem müssen die Herstellungs- und Testkosten gering bleiben und die Produkteinführungsfristen so kurz wie möglich gehalten werden. Daraus folgt, dass ein Testingenieur, der auf Leiterplatten-Ebene arbeitet, die Herstellungsfehler so früh wie möglich entdecken und dabei möglichst niedrige Kosten verursachen soll. Allerdings sind die klassischen Testmethoden nicht in der Lage, die Anforderungen von modernen Leiterplatten zu erfüllen und im schlimmsten Fall können diese Testmethoden überhaupt nicht verwendet werden. Dies liegt vor allem an modernen Gehäuse-Technologien, der hohen Bauteildichte und den hohen Arbeitsfrequenzen von modernen Leiterplatten. Das führt zu sehr langen Testzeiten, geringer Testabdeckung und hohen Testkosten. Die Dissertation greift diese Problematik auf und liefert einen FPGA-basierten Testansatz für Leiterplatten. Das Konzept beruht auf einem konfigurierbaren Testprozessor, welcher im On-Board-FPGA temporär implementiert wird und die entsprechenden Mechanismen für die Kommunikation mit der externen Testeinrichtung und Co-Prozessoren im FPGA bereitstellt. Dadurch ist es möglich Testfunktionen flexibel entweder auf der externen Testeinrichtung oder auf dem FPGA zu implementieren. Auf diese Weise werden Tests at-speed ausgeführt, um die Testabdeckung zu erhöhen. Außerdem wird die Testzeit verkürzt und das Testsystem automatisch an die Eigenschaften des FPGAs und anderer Bauteile auf der Leiterplatte angepasst. Ein wesentlicher Teil des FPGA-basierten Testansatzes umfasst die Entwicklung eines Testprozessors. In dieser Dissertation wird über die benötigten Eigenschaften des Prozessors diskutiert und es wird gezeigt, dass die Anpassung des Prozessors an den spezifischen Testfall von großer Bedeutung für die Optimierung ist. Zu diesem Zweck wird der Prozessor mit Konfigurationsparametern auf der Befehlssatzarchitektur-Ebene und Mikroarchitektur-Ebene ausgerüstet. Außerdem wird ein automatischer Generierungsprozess für die Realisierung des Testsystems und für die Berechnung einer Untergruppe von Konfigurationsparametern des Prozessors vorgestellt. Der automatische Generierungsprozess benutzt als Eingangsinformation ein Modell des Prüflings (device under test model, DUT-M). Das entwickelte Testsystem wurde zum Testen von Leiterplatten für Verbindungen zwischen dem FPGA und zwei Bauteilen verwendet, um den FPGA-basierten Testansatz und die Durchführbarkeit des Testprozessors für das Testen auf Leiterplatte-Ebene zu evaluieren. Die zwei Bauteile sind ein Speicher mit direktem Zugriff (static random-access memory, SRAM) und eine Flüssigkristallanzeige (liquid crystal display, LCD). Die Experimente wurden durchgeführt, um den Ressourcenverbrauch des Prozessors und Testsystems festzustellen und um die Testzeit zu messen. Dies geschah durch die Implementierung von unterschiedlichen Testfunktionen auf der externen Testeinrichtung und dem FPGA. Dadurch konnte gezeigt werden, dass der FPGA-basierte Ansatz für das Testen von Leiterplatten geeignet ist und dass der Testprozessor eine realistische Alternative für das Testen auf Leiterplatten-Ebene ist

Enhancing Real-time Embedded Image Processing Robustness on Reconfigurable Devices for Critical Applications

Nowadays, image processing is increasingly used in several application fields, such as biomedical, aerospace, or automotive. Within these fields, image processing is used to serve both non-critical and critical tasks. As example, in automotive, cameras are becoming key sensors in increasing car safety, driving assistance and driving comfort. They have been employed for infotainment (non-critical), as well as for some driver assistance tasks (critical), such as Forward Collision Avoidance, Intelligent Speed Control, or Pedestrian Detection. The complexity of these algorithms brings a challenge in real-time image processing systems, requiring high computing capacity, usually not available in processors for embedded systems. Hardware acceleration is therefore crucial, and devices such as Field Programmable Gate Arrays (FPGAs) best fit the growing demand of computational capabilities. These devices can assist embedded processors by significantly speeding-up computationally intensive software algorithms. Moreover, critical applications introduce strict requirements not only from the real-time constraints, but also from the device reliability and algorithm robustness points of view. Technology scaling is highlighting reliability problems related to aging phenomena, and to the increasing sensitivity of digital devices to external radiation events that can cause transient or even permanent faults. These faults can lead to wrong information processed or, in the worst case, to a dangerous system failure. In this context, the reconfigurable nature of FPGA devices can be exploited to increase the system reliability and robustness by leveraging Dynamic Partial Reconfiguration features. The research work presented in this thesis focuses on the development of techniques for implementing efficient and robust real-time embedded image processing hardware accelerators and systems for mission-critical applications. Three main challenges have been faced and will be discussed, along with proposed solutions, throughout the thesis: (i) achieving real-time performances, (ii) enhancing algorithm robustness, and (iii) increasing overall system's dependability. In order to ensure real-time performances, efficient FPGA-based hardware accelerators implementing selected image processing algorithms have been developed. Functionalities offered by the target technology, and algorithm's characteristics have been constantly taken into account while designing such accelerators, in order to efficiently tailor algorithm's operations to available hardware resources. On the other hand, the key idea for increasing image processing algorithms' robustness is to introduce self-adaptivity features at algorithm level, in order to maintain constant, or improve, the quality of results for a wide range of input conditions, that are not always fully predictable at design-time (e.g., noise level variations). This has been accomplished by measuring at run-time some characteristics of the input images, and then tuning the algorithm parameters based on such estimations. Dynamic reconfiguration features of modern reconfigurable FPGA have been extensively exploited in order to integrate run-time adaptivity into the designed hardware accelerators. Tools and methodologies have been also developed in order to increase the overall system dependability during reconfiguration processes, thus providing safe run-time adaptation mechanisms. In addition, taking into account the target technology and the environments in which the developed hardware accelerators and systems may be employed, dependability issues have been analyzed, leading to the development of a platform for quickly assessing the reliability and characterizing the behavior of hardware accelerators implemented on reconfigurable FPGAs when they are affected by such faults

Memory hierarchy and data communication in heterogeneous reconfigurable SoCs

The miniaturization race in the hardware industry aiming at continuous increasing of transistor density on a die does not bring respective application performance improvements any more. One of the most promising alternatives is to exploit a heterogeneous nature of common applications in hardware. Supported by reconfigurable computation, which has already proved its efficiency in accelerating data intensive applications, this concept promises a breakthrough in contemporary technology development. Memory organization in such heterogeneous reconfigurable architectures becomes very critical. Two primary aspects introduce a sophisticated trade-off. On the one hand, a memory subsystem should provide well organized distributed data structure and guarantee the required data bandwidth. On the other hand, it should hide the heterogeneous hardware structure from the end-user, in order to support feasible high-level programmability of the system. This thesis work explores the heterogeneous reconfigurable hardware architectures and presents possible solutions to cope the problem of memory organization and data structure. By the example of the MORPHEUS heterogeneous platform, the discussion follows the complete design cycle, starting from decision making and justification, until hardware realization. Particular emphasis is made on the methods to support high system performance, meet application requirements, and provide a user-friendly programmer interface. As a result, the research introduces a complete heterogeneous platform enhanced with a hierarchical memory organization, which copes with its task by means of separating computation from communication, providing reconfigurable engines with computation and configuration data, and unification of heterogeneous computational devices using local storage buffers. It is distinguished from the related solutions by distributed data-flow organization, specifically engineered mechanisms to operate with data on local domains, particular communication infrastructure based on Network-on-Chip, and thorough methods to prevent computation and communication stalls. In addition, a novel advanced technique to accelerate memory access was developed and implemented

A Micro Power Hardware Fabric for Embedded Computing

Field Programmable Gate Arrays (FPGAs) mitigate many of the problemsencountered with the development of ASICs by offering flexibility, faster time-to-market, and amortized NRE costs, among other benefits. While FPGAs are increasingly being used for complex computational applications such as signal and image processing, networking, and cryptology, they are far from ideal for these tasks due to relatively high power consumption and silicon usage overheads compared to direct ASIC implementation. A reconfigurable device that exhibits ASIC-like power characteristics and FPGA-like costs and tool support is desirable to fill this void. In this research, a parameterized, reconfigurable fabric model named as domain specific fabric (DSF) is developed that exhibits ASIC-like power characteristics for Digital Signal Processing (DSP) style applications. Using this model, the impact of varying different design parameters on power and performance has been studied. Different optimization techniques like local search and simulated annealing are used to determine the appropriate interconnect for a specific set of applications. A design space exploration tool has been developed to automate and generate a tailored architectural instance of the fabric.The fabric has been synthesized on 160 nm cell-based ASIC fabrication process from OKI and 130 nm from IBM. A detailed power-performance analysis has been completed using signal and image processing benchmarks from the MediaBench benchmark suite and elsewhere with comparisons to other hardware and software implementations. The optimized fabric implemented using the 130 nm process yields energy within 3X of a direct ASIC implementation, 330X better than a Virtex-II Pro FPGA and 2016X better than an Intel XScale processor

Microarchitectural Low-Power Design Techniques for Embedded Microprocessors

With the omnipresence of embedded processing in all forms of electronics today, there is a strong trend towards wireless, battery-powered, portable embedded systems which have to operate under stringent energy constraints. Consequently, low power consumption and high energy efficiency have emerged as the two key criteria for embedded microprocessor design. In this thesis we present a range of microarchitectural low-power design techniques which enable the increase of performance for embedded microprocessors and/or the reduction of energy consumption, e.g., through voltage scaling. In the context of cryptographic applications, we explore the effectiveness of instruction set extensions (ISEs) for a range of different cryptographic hash functions (SHA-3 candidates) on a 16-bit microcontroller architecture (PIC24). Specifically, we demonstrate the effectiveness of light-weight ISEs based on lookup table integration and microcoded instructions using finite state machines for operand and address generation. On-node processing in autonomous wireless sensor node devices requires deeply embedded cores with extremely low power consumption. To address this need, we present TamaRISC, a custom-designed ISA with a corresponding ultra-low-power microarchitecture implementation. The TamaRISC architecture is employed in conjunction with an ISE and standard cell memories to design a sub-threshold capable processor system targeted at compressed sensing applications. We furthermore employ TamaRISC in a hybrid SIMD/MIMD multi-core architecture targeted at moderate to high processing requirements (> 1 MOPS). A range of different microarchitectural techniques for efficient memory organization are presented. Specifically, we introduce a configurable data memory mapping technique for private and shared access, as well as instruction broadcast together with synchronized code execution based on checkpointing. We then study an inherent suboptimality due to the worst-case design principle in synchronous circuits, and introduce the concept of dynamic timing margins. We show that dynamic timing margins exist in microprocessor circuits, and that these margins are to a large extent state-dependent and that they are correlated to the sequences of instruction types which are executed within the processor pipeline. To perform this analysis we propose a circuit/processor characterization flow and tool called dynamic timing analysis. Moreover, this flow is employed in order to devise a high-level instruction set simulation environment for impact-evaluation of timing errors on application performance. The presented approach improves the state of the art significantly in terms of simulation accuracy through the use of statistical fault injection. The dynamic timing margins in microprocessors are then systematically exploited for throughput improvements or energy reductions via our proposed instruction-based dynamic clock adjustment (DCA) technique. To this end, we introduce a 6-stage 32-bit microprocessor with cycle-by-cycle DCA. Besides a comprehensive design flow and simulation environment for evaluation of the DCA approach, we additionally present a silicon prototype of a DCA-enabled OpenRISC microarchitecture fabricated in 28 nm FD-SOI CMOS. The test chip includes a suitable clock generation unit which allows for cycle-by-cycle DCA over a wide range with fine granularity at frequencies exceeding 1 GHz. Measurement results of speedups and power reductions are provided