Enhanced FPGA reliability through efficient run-time fault reconfiguration

Field Programmable Gate Arrays (FPGAs) have been indispensable components of embedded systems and datacenter infrastructures. However, energy efficiency of FPGAs has become a hard barrier preventing their expansion to more application contexts, due to two physical limitations: (1) The massive usage of routing multiplexers causes delay and power overheads as compared to ASICs. To reduce their power consumption, FPGAs have to operate at low supply voltage but sacrifice performance because the transistors drive degrade when working voltage decreases. (2) Using volatile memory technology forces FPGAs to lose configurations when powered off and to be reconfigured at each power Resistive Random Access Memories (RRAMs) have strong potentials in overcoming the physical limitations of conventional FPGAs. First of all, RRAMs grant FPGAs non-volatility, enabling FPGAs to be Normally powered off, Instantly powered on. Second, by combining functionality of memory and pass-gate logic in one unique device, RRAMs can greatly reduce area and delay of routing elements. Third, when RRAMs are embedded into datpaths, the performance of circuits can be independent from their working voltage, beyond the limitations of CMOS circuits. However, researches and development of RRAM-based FPGAs are in their infancy. Most of area and performance predictions were achieved without solid circuit-level simulations and sophisticated Computer Aided Design (CAD) tools, causing the predicted improvements to be less convincing. In this thesis,we present high-performance and low-power RRAM-based FPGAs fromtransistorlevel circuit designs to architecture-level optimizations and CAD tools, using theoretical analysis, industrial electrical simulators and novel CAD tools. We believe that this is the first systematic study in the field, covering: From a circuit design perspective, we propose efficient RRAM-based programming circuits and routing multiplexers through both theoretical analysis and electrical simulations. The proposed 4T(ransitor)1R(RAM) programming structure demonstrates significant improvements in programming current, when compared to most popular 2T1R programming structure. 4T1R-based routingmultiplexer designs are proposed by considering various physical design parasitics, such as intrinsic capacitance of RRAMs and wells doping organization. The proposed 4T1R-based multiplexers outperformbest CMOS implementations significantly in area, delay and power at both nominal and near-Vt regime. From a CAD perspective, we develop a generic FPGA architecture exploration tool, FPGASPICE, modeling a full FPGA fabric with SPICE and Verilog netlists. FPGA-SPICE provides different levels of testbenches and techniques to split large SPICE netlists, in order to obtain better trade-off between simulation time and accuracy. FPGA-SPICE can capture area and power characteristics of SRAM-based and RRAM-based FPGAs more accurately than the currently best analyticalmodels. From an architecture perspective, we propose architecture-level optimizations for RRAMbased FPGAs and quantify their minimumrequirements for RRAM devices. Compared to the best SRAM-based FPGAs, an optimized RRAM-based FPGA architecture brings significant reduction in area, delay and power respectively. In particular, RRAM-based FPGAs operating in the near-Vt regime demonstrate a 5x power improvement without delay overhead as compared to optimized SRAM-based FPGA operating at nominal working voltage.

A low power CMOS Static Random Access Memory (SRAM) based Field Programmable Gate Arrays (FPGA) architecture is being presented in this paper. The architecture presented here is based on CMOS logic and CMOS SRAMs that are used for on-chip dynamic reconfiguration. This architecture employs the fast and low-power SRAM blocks that are based on 10T SRAM cells. These blocks are employed in fast access of the configuration bits by using the shadow SRAM technique. The dynamic reconfiguration delay is being hidden behind the computation delay through the use of shadow SRAM cells. The combined effect of both the SRAM memory cells and the shadow SRAM scheme enables to support in reducing the delay and also to achieve reduced power consumption. Experimental results show reduced delay of about 8.035ns and power consumption of about 0.015W for the 10T SRAM memory cell with an overhead in area, relative to 4T and 6T SRAM cells. Also, the experimental results include the values of delay of about 8.979ns and power consumption of about 0.052W, achieved for the LB of FPGA architecture which employs CMOS SRAMs using the 10T SRAM memory cells in it.

The type of Field Programmable Gate Arrays (FPGAs) technology and device family used in a design is a key factor for system reliability. Though antifuse-based FPGAs are widely used in aerospace because of their high reliability, current antifuse-based FPGA devices are expensive and leave no room for mistakes or changes since they are not reprogrammable. The substitute for antifuse-based FPGAs are needed in aerospace design, they should be both reprogrammable and highly reliable to Single Event Upset effects (SEUs). SRAM-based FPGAs are widely and systematically used in complex embedding digital systems both in a single chip industry and commercial applications. They are reprogrammable and high in density because of the smaller SRAM cells and logic structures. But the SRAM-based FPGAs are especially sensitive to cosmic radiation because the configuration information is stored in SRAM memory. The ideal FPGA for aerospace use should be high-density SRAM-based which is also insensitive to cosmic radiation induced SEUs. Therefore, in order to enable the use of SRAM-based FPGAs in safety critical applications, new techniques and strategies are essential to mitigate the SEU errors in such devices. In order to improve the reliability of SRAM-based FPGAs which are very sensitive to SEU errors, techniques such as reconfiguration and Triple Module Redundancy (TMR) are widely used in the aerospace electronic systems to mitigate the SEU and Single Event Functional Interrupt (SEFI) errors. Compared to reconfiguration and triplication, scrubbing and partial reconfiguration will utilize fewer or even no internal resources of FPGA. What's more, the detection and repair process can detect and correct SEU errors in configuration memories of the FPGA without affecting or interrupting the proper working of the system while reconfiguration would terminate the operation of the FPGA. This paper presents a payload system realized on Xilinx Virtex-4 FPGA which mitigates SEU effects in the internal FPGA by implementing scrubbing strategy and thus improve the reliability of the whole system.

The growing complexity of embedded systems makes reconfiguration and embedded OSs (Operating Systems) more and more interesting. FPGAs (Field-Programmable Gate Arrays) are able to perform such a feature with success. With most of the FPGAs, the OS is stored into an external memory (usually Flash) and running on a processor embedded into the FPGA. We consider that FPGA embedded processor is able to process the OS update through, for instance, an insecure network. However, these features may give rise to security flaws affecting the system integrity or freshness. Integrity can be altered by spoofing or modifying data in order to introduce malicious code. In the same way, freshness can be affected by replaying an old configuration in order to downgrade the system. This work proposes a trusted computing mechanism taking into account the whole security chain from bit stream-to-kernel-boot ensuring, both hardware and software, integrity while preventing replay attacks. This paper summarizes the current counter-measures ensuring integrity, confidentiality and freshness of the bit stream. Then we propose a solution to protect OS kernel against malicious modifications thanks to already trusted bit stream power-up. We also evaluate the area and performance overhead of the proposed architecture and its improvement using asymmetric cryptography. Adding security and increasing performances, this solution generates between 0 and 40% of area overhead depending on the re-usability consideration.

Although redundant addition is widely used to design parallel multioperand adders for ASIC implementations, the use of redundant adders on Field Programmable Gate Arrays (FPGAs) has generally been avoided. The main reasons are the efficient implementation of carry propagate adders (CPAs) on these devices (due to their specialized carry-chain resources) as well as the area overhead of the redundant adders when they are implemented on FPGAs. This paper presents different approaches to the efficient implementation of generic carry-save compressor trees on FPGAs. They present a fast critical path, independent of bit width, with practically no area overhead compared to CPA trees. Along with the classic carry-save compressor tree, we present a novel linear array structure, which efficiently uses the fast carry-chain resources. This approach is defined in a parameterizable HDL code based on CPAs, which makes it compatible with any FPGA family or vendor. A detailed study is provided for a wide range of bit widths and large number of operands. Compared to binary and ternary CPA trees, speedups of up to 2.29 and 2.14 are achieved for 16-bit width and up to 3.81 and 3.11 for 64-bit width.

Chapter 5 - FPGA Device-Level Design Decisions

Managing leakage power in field programmable gate arrays (FPGAs) has become critical for the FPGA industry to remain competitive in the semiconductor market and enter the mobile applications domain. This paper proposes and evaluates several dual-Vt-based designs of FPGA architecture for reducing the leakage power. A dual-Vt FPGA computer-aided design (CAD) framework has been proposed, which is used to develop and evaluate different dual-Vt FPGA architectures. The logic elements and the routing resources are considered as candidates for dual-Vt assignment. The authors estimate the number of the logic elements that can be assigned as high-Vt in the ideal case by using a dual-Vt assignment algorithm in the CAD framework. Based upon this estimate, the authors develop and evaluate two kinds of architectures, homogenous and heterogenous. The results indicate that an average leakage-power savings of up to 50% can be obtained from these architectures. This CAD framework can also be used for developing and evaluating different dual-Vt FPGA architectures other than the ones proposed in this paper

The demand for high-performance computing and rapidly increasing power consumption has increased the necessity for application-specific accelerators. In the datacenter and mobile system, more applications are increasingly relying on accelerators. Field-programmable gate arrays (FPGAs) emerge as a good candidate because they have high programmability and power efficiency. As the number of applications requiring acceleration increases, there is huge demand for FPGAs that support multiple contexts. Previous FPGA designs that support multicontext have various shortcomings such as volatility, poor power efficiency, large performance, area, and reconfiguration overhead. In this article, we propose a spin-transfer torque magnetic RAM (STT-MRAM)-based nonvolatile multicontext FPGA (NVMC-FPGA) that overcomes these shortcomings. We introduce the NVMC-FPGA architecture and operation modes that take advantage of nonvolatility and support multicontext. We also develop the multicontext-aware FPGA computer aided design flow to make the most of the NVMC-FPGA. Compared to the conventional SRAM-based FPGA, when eight identical circuits are mapped, the NVMC-FPGA improves the performance by 15.3% on average and reduces the power consumption by 11.2%–80.7%, depending on the number of simultaneously activated circuits. Moreover, when eight different circuits are mapped, the NVMC-FPGA improves the performance by 58.5% on average and reduces the power consumption by 6.2%–63.3%, depending on the number of simultaneously activated circuits.

The application diversity and evolution of AI accelerator architectures require innovative DFT solutions to address issues such as test time, test power, performance and area overhead. Full scan DFT, because of its enhanced controllability and observability, is an industrial de facto test strategy. However, it may not yield an optimal test solution with stringent design constraints of edge-based AI accelerators. In this paper, a novel test architecture based on selective-partial scan is proposed for performance, power and area (PPA) overhead constrained edge-based systolic AI accelerator. In this architecture, the structural test patterns are applied partly in functional manner, which reduces the testability problem of an array to that of a single processing element (PE); thus, resulting in reduced test time and test data volume. Moreover, a delay fault testing method based on Launch-on-Capture is presented for the partial scan based proposed architecture. Experimental results show that proposed architecture is efficient in terms of test power and test time when compared to full scan DFT.

Field Programmable Gate Arrays (FPGAs) have become a popular medium for the implementation of many digital circuits. Mapping applications into FPGAs requires a set of efficient Computer-Aided Design (CAD) tools to obtain high-quality Integrated Circuits (ICs). One critical issue of FPGA implementation is the quality and efficiency of associated CAD algorithms. In this paper, we are interested in investigating clustering algorithms aspect to optimize Mesh of Clusters (MoCs) FPGA performance. In fact, the way we distribute Logic Blocks (LBs) between FPGA clusters has an important impact on performance. In this paper, we explore the effects of two clustering algorithms (First Choice (FC) and T-VPack) on MoCs FPGA architecture based only on short routing wires. This paper highlights and experimentally demonstrates that FC clustering algorithm ameliorates power consumption, area, critical path delay and energy by an average of 17%, 11%, 13% and 24% respectively compared to T-VPack for MoCs FPGA.

Due to technology advances and complexity of designs, thermal issue is a bottleneck in electronics designs. Various dynamic thermal management techniques have been proposed to address this issue. To effectively apply thermal management techniques, providing an accurate thermal map of chips is highly required. For this goal, a network of temperature sensors ought to be provided. There are various implementations for temperature sensors and network of sensors on Field Programmable Gate Arrays (FPGAs). This work defines and formulates four metrics and criteria, in terms of area, thermal, and power overheads and thermal map accuracy for exploring and evaluating efficiency of different implementations of Ring Oscillator-based Temperature Sensor (ROTS) networks on FPGAs and reports the comparison results for 12 networks with various sensor configurations. According to our metrics and experiments, the sensor that it is composed of NOT gates with open latches and RNS ring counter has lower thermal and power overheads compared to other configurations. Moreover, in this work, a new ROTS is presented that occupies 25% less resources than the most compact temperature sensor. Also, it provides 1.72 times higher sensitivity than the best sensitive ROTS design.

An FPGA (Field Programmable Gate Array) based distributed IP (Intellectual Property) watermarking method is presented for reusable IP protection. The signature is encrypted by the hash algorithm MD5, generating 128 bits digital digest. The digest is then transformed into watermark positions and watermark bits with high security. The watermark bits is finally embedded into the LUTs(Lookup Table) of FPGA design by identical logic configuration. The normal function of original design will not change and the actual embedded watermark is reduced drastically due to the transformation. The experimental results on Xilinx Virtex II Pro XC2VP4 FPGA show low resource and timing overhead and high security by comparing with other method.

Hardware acceleration using field programmable gate arrays (FPGAs) has become increasingly popular for computationally intensive digital signal processing (DSP) applications. Unfortunately, while FPGAs have a reasonably tractable computer aided design (CAD) flow and performance, they have poor power characteristics when compared to direct application specific integrated circuit (ASIC) fabrication. ASICs exhibit better performance and power than FPGAs, but require complex CAD and large non-recurring engineering (NRE) costs. A reconfigurable device that exhibits ASIC-like power characteristics and FPGA-like costs and tool support is desirable to fill this void. Several coarse-grained fabric architectures proposed during the last decade have been focused on performance and area-efficient architectural techniques. Even though power is becoming one of the critical design concerns for semiconductor industry, this issue has not been adequately addressed in the existing coarse-grained fabric architectures. In this paper, a low-power and high-performance hardware acceleration engine for DSP style applications is described. This reconfigurable fabric model is generic and parameterizable allowing design parameters to be adjusted within the architecture. The impact of varying different design parameters such as functional unit granularity, and multiplexer cardinality are studied for their implications on power and performance. The low-power fabric was designed to operate within the SuperCISC processor architecture designed at the University of Pittsburgh

3 - Configurable Computing

Background: In recent years, the rising demand for high-performance radar systems in aeronautics, astronautics, national defense, and civil communication has driven the widespread application of phased-array technology. The design of beam controllers, the core of phased-array systems, faces many challenges. Traditional implementation schemes are usually based on application-specific integrated circuits (ASIC) or discrete components, which have a long development cycle, poor flexibility, and limited adaptability. Field-programmable gate arrays (FPGA), with their high parallelism, reconfigurability, and powerful signal processing capabilities, offer a new way to implement phased-array control systems. But FPGA design has traditionally relied on register transfer level (RTL) description, which is inefficient and struggles to keep up with the rapid iteration of complex algorithms. With the development of high-level synthesis (HLS) technology, it has become possible to develop FPGAs using high-level languages such as C/C++. However, improving development efficiency while ensuring hardware performance remains a key issue in the design of phased-array beam controllers. Materials and Methods: This study employs an HLS - RTL co - design method to build a phased - array beam controller. This approach combines the strengths of HLS's efficient algorithm implementation and RTL's precise hardware interface control. The system architecture consists of three parts: the host - machine control layer, FPGA processing layer, and phase - control output layer. In the FPGA processing layer, the core beam - forming algorithm is implemented via HLS. Based on phased - array principles, this algorithm converts target angles to wave vectors and calculates phase - compensation values for each element in an 8×8 array. Pipelining and parallel processing techniques are used in the HLS design to optimize algorithm throughput and latency. The phase - control output layer, designed with RTL, repackages 64 calculated phase values and distributes them to 16 physical phase - shifter chips. Each phase - shifter manages four elements and receives control data through an SPI interface. Results: The proposed FPGA-based phased-array beam controller design in this paper has successfully achieved high - speed, high - precision beam control. By using the HLS - RTL co - design method, it has solved the problem of low algorithm implementation efficiency in traditional FPGA development and ensured the high performance and reliability of hardware interfaces. Experimental results indicate that the system meets or surpasses design targets on key performance indicators. Its end - to - end latency is kept within 130μs, it supports an angle update rate of over 5,000 times per second, and can satisfy the requirements for tracking highly dynamic targets in practical applications. Conclusion: The major contributions of this research are as follows: presenting an HLS - RTL co - design methodology for complex FPGA system development; designing an efficient phased - array beam - forming algorithm and its hardware implementation; and developing a flexible and scalable phased - array control system architecture that supports different array configurations. These findings are highly significant for beamforming technologies in phased - array radar and 5G communication systems, as well as for other FPGA applications requiring high - speed signal processing.