Organic embedded architecture for sustainable FPGA soft-core processors

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.

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.

On-board reconfiguration of FPGAs on a spacecraft offers the important advantage of allowing the reuse of the same hardware component for different functionalities during a mission. To be able to benefit from these features, a solution to cope with the challenges of using SRAMbased FPGAs in a radiation environment is required, and at the same time it is desired that the FPGA reconfiguration takes place at high speed. The BRAVE NG-MEDIUM FPGA offers a solution for this problem, by combining being radiation-hardened by design and reconfiguration of the programmable logic via a high-speed communication protocol, namely SpaceWire. In this paper we compare the performance of SpaceWire with Joint Test Action Group (JTAG) for NG-MEDIUM reconfiguration, in terms of the time elapsed when uploading a bitstream file from a Central Processing Unit (in our case from a computer) to the Field Programmable Gate Array (FPGA) and the time needed for uploading such bitstream and configuring the FPGA with the uploaded bitstream.

Recently, static random access memory (SRAM)-based field programmable gate arrays (FPGAs) are used for various systems. Since such SRAM-based FPGAs are programmable, their use over a long period must accommodate the use of a partly damaged programmable gate array. However, since current FPGAs use a serial configuration line for their configuration and the serial configuration circuit is invariably first broken circuit. Therefore, currently available FPGAs cannot accommodate the use of a partly damaged programmable gate array. However, if a partly damaged programmable gate array could be used, then the lifetime of VLSIs would be increased drastically. To extend the lifetime of programmable devices, FPGA should use a parallel configuration architecture instead of the serial configuration architecture of currently available FPGAs. This paper therefore clarifies the benefits of the parallel configuration architecture on an optically re-configurable gate array (ORGA) VLSI using the designs of an ORGA-VLSI and a currently available serial-configuration FPGA.

Self-healing reconfigurable logic using autonomous group testing

Modern SRAM-based field programmable gate array (FPGA) devices offer high capability in implementing complex system. Unfortunately, SRAM-based FPGAs are extremely sensitive to single event upsets (SEUs) induced by radiation particles. In order to successfully deploy safety- or mission-critical applications, designer need to validate the correctness of the obtained designs. In this paper we describe a system based on partial-reconfiguration for running fault-injection experiments within the configuration memory of SRAM-based FPGAs. The proposed fault-injection system uses the internal configuration capabilities that modern FPGAs offer in order to inject SEU within the configuration memory. Detailed experimental results show that the technique is orders of magnitude faster than previously proposed ones.

Recently, many researches have investigated efficient reverse engineering methods to restore Programmable Logic Points (PLPs) and Programmable Interconnect Points (PIPs) in SRAM-based Field Programmable Gate Arrays (FPGAs). However, the research on the restoration of Programmable Content Points (PCPs) such as memory data are rarely studied. In this paper, we propose an efficient reverse engineering method to recover Read Only Memory (ROM) data, which is essential for the implementation of modern digital circuits. First, we analyze the FPGA hardware resources mapped to Xilinx primitive library of ROM, and next the proposed reverse engineering process is explained using mapping relation between ROM data and hardware resources. As an example, XC3S50 FPGA of Xilinx Sparatan-3 family is utilized, and the process of restoring the SBOX of AES (Advanced Encryption Standard) is provided as a practical application.

This paper presents a new design for testing and diagnosing the SRAM-based field programmable gate arrays (FPGA). By slightly modifying the original FPGA's SRAM memory, the new architecture permits the configuration data to be looped on a chip. Then the full testing and diagnosing of the FPGA are achieved by loading typically only one testing configuration datum (carefully chosen) instead of loading the total required configurations data (which is a very slow process) in the normal cases. Other configurations data are obtained by shifting the first one inside the chip. Consequently the test becomes faster. This method does not need a large outside memory (off-chip memory) for the test. The evaluation proves that this method becomes very interesting when the complexity of the configurable blocks (CLBs) or the chip size increase.

Datacenter workloads demand high computational capabilities, flexibility, power efficiency, and low cost. It is challenging to improve all of these factors simultaneously. To advance datacenter capabilities beyond what commodity server designs can provide, we designed and built a composable, reconfigurable hardware fabric based on field programmable gate arrays (FPGA). Each server in the fabric contains one FPGA, and all FPGAs within a 48-server rack are interconnected over a low-latency, high-bandwidth network. We describe a medium-scale deployment of this fabric on a bed of 1632 servers, and measure its effectiveness in accelerating the ranking component of the Bing web search engine. We describe the requirements and architecture of the system, detail the critical engineering challenges and solutions needed to make the system robust in the presence of failures, and measure the performance, power, and resilience of the system. Under high load, the large-scale reconfigurable fabric improves the ranking throughput of each server by 95% at a desirable latency distribution or reduces tail latency by 29% at a fixed throughput. In other words, the reconfigurable fabric enables the same throughput using only half the number of servers.

Continuous shrinking of transistor size to provide high computation capability along with low power consumption has been accompanied by reliability degradations due to e.g., aging phenomenon. In this regard, with huge number of configuration bits, Field-Programmable Gate Arrays (FPGAs) are more susceptible to aging since aging not only degrades the performance, it may additionally result in corrupting the configuration cells and thus causing permanent circuit malfunctioning. While several works have investigated the aging effects in Look-Up Tables (LUTs), the routing fabric of these devices is seldom studied - even though it contributes to the majority of FPGAs' resources and configuration bits. Furthermore, there is a high prospect that errors in its state to propagate to the device outputs. In this paper, we first investigate aging effects in the routing fabric of FPGAs with respect to performance and reliability degradations. Based on this investigation, we enhance the conventional routing algorithm to mitigate the impact of aging by increasing the recovery time (i.e., the mechanism used to heal aging-induced defects) of transistors used in the routing resources. We examine our proposed method as reduction in stress time and required guardband to protect against aging in the routing fabric, as well as in improving the FPGA's lifetime. Our experiments show that the proposed method reduces the average stress time and aging-induced delay of routing resources by 41% and 18.3%, respectively. This, in turn, leads to improving the device lifetime by 130% compared to baseline routing. The proposed method can be applied by simple amending of conventional routing algorithms. Thus, it incurs negligible delay overhead.

The desirable use of Field-Programmable Gate Arrays (FPGAs) in aerospace & defense field has become a general consensus among IC and embedded system designers. Radiation-hardened (rad-hard) electronics used in this domain is regulated under severe and complex political and commercial treaties. In order to refrain from these undesired political and commercial barriers COTS FPGAs (despite the fact of their low reliability) have been considered as a promising alternative to replace rad-hard ICs. Moreover, SRAM-based FPGAs are pretermitted with respect to flash or anti-fuse devices. In this scenario, this paper analyses, by means of heavy-ion accelerator experiments, the Single-Event Upset (SEU) tolerance of the Microsemi ProAsic3E A3PE1500 COTS FPGA. This component is under pre-qualification process for use in some satellites of the Brazilian Space Program. Preliminary results are herein briefly presented and discussed. These experimental results allow us to consider this component as a strong candidate to replace rad-hard FPGAs, if its use is combined with strict system-level fault-tolerant strategies for error detection and correction.

International audience

This paper presents a new design for testing SRAM-based field programmable gate arrays (FPGAs). The original SRAM part is modified a bit so that the FPGA gets the ability to automatically shift the data on-chip and then the test becomes faster. This method does not need a large outside memory (off-chip memory) for saving the test data. It is proved that this method detects multiple faults and covers 100%; of modeled faults. The simulation results of Xilinix XC4000 family, using CAD tools, shows that the routing and the placement of this method are easily achieved.

SRAM-based field programmable gate arrays (FPGAs) are widely used in mission-critical applications, such as aerospace and avionics. Due to the increasing working frequency and technology scaling of ultra-nanometer technology, single event transients (SETs) are becoming a major source of errors for these devices. In this paper, we propose a workflow for evaluating the behavior of SETs in SRAM-based FPGAs. The method is able to compute the propagation-induced pulse broadening (PIPB) effect introduced by the logic resources traversed by transient pulses. Besides, we developed an accurate look-up table (LUT) layout model able to effectively predict the kinds of the SETs induced by radiation-particle and to accurately mimic the phenomena of the SET generation and propagation. The proposed methodology is applicable to any recent technology to provide the SET analysis, necessary for an efficient mitigation technology. The experimental results achieved from a set of benchmark circuits mapped on a 28-nm SRAM-based FPGA and compared with the fault injection experiments demonstrate the effectiveness of our technique.

According to the goal of independent college to cultivate application service-oriented talents.The paper presents the field programmable gate array(FPGA),Quartus II and Verilog HDL knowledge to the teaching method in the teaching of digital logic circuit using the combinational logic circuits and sequential logic circuits as a design example.The teaching practice shows that this teaching method can motivate students interest in learning.It plays a positive role in promoting students practice ability and innovation consciousness,thus enhance the teaching quality.