SRAM-based Field Programmable Gate Arrays Research Articles

A New Algorithm for the Analysis of the MCUs Sensitiveness of TMR Architectures in SRAM-Based FPGAs

In this paper we present an analytical analysis of the fault masking capabilities of triple modular redundancy (TMR) hardening techniques in the presence of multiple cell upsets (MCUs) in the configuration memory of SRAM-based field-programmable gate arrays (FPGAs). The analytical method we developed allows an accurate study of the MCUs provoking domain crossing errors that defeat TMR. From our analysis we have found that most of the failures affect configurable logic block's routing resources. The experimental analysis has been performed on two realistic case study circuits. Experimental results are presented and discussed showing in particular that 2-bits MCUs may corrupt TMR 2.6 orders of magnitude more than single cell upsets (SCUs).

New Non-Volatile Memory Structures for FPGA Architectures

A new set of programmable elements (PEs) using a new non-volatile device for use with routing switches and logical elements within a field-programmable gate array (FPGA) is described. The PEs have small area, can be combined with components that use low operational voltage on the same CMOS logic process, are non-volatile, enable the use of fast thin-oxide pass transistors, and are reprogrammable. A novel non-volatile flip-flop for use within the logical elements is presented as well. In combination, these methods enable programmable logic devices with improved area efficiency, the speed advantages of SRAM-based FPGAs, and a wide range of opportunities for power down strategies.

A New Partial Reconfiguration-Based Fault-Injection System to Evaluate SEU Effects in SRAM-Based FPGAs

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.

Sharing of SRAM Tables Among NPN-Equivalent LUTs in SRAM-Based FPGAs

This article introduces a novel lookup table (LUT) and its usage in the configurable logic block (CLB) architectures for SRAM-based field-programmable gate array (FPGA) architectures. The proposed CLB allows sharing of SRAM tables of LUTs among NPN-equivalent functions to reduce the size of memories used for storing the functions and also reduces the number of configuration bits required. We measured many different characteristics of FPGAs using our new CLB architecture, including area, delay, routing, and power requirements. We experimentally found that for many different FPGA architectures, CLBs can share one-fourth of their SRAM tables between two basic logic elements (BLEs), which reduced both power consumption and area without negatively affecting routing or wirelength, and there was only a negligible increase in critical path delay of 0.27%. Specifically, we find that FPGAs consisting of CLBs with 16 BLEs and 34 inputs can be implemented with eight normal SRAMs and four SRAMs shared between two BLEs, for an overall reduction of four out of sixteen SRAM tables per CLB. With this new CLB architecture, we measured an approximate reduction in overall power consumption of 2% and an estimated reduction in area of 3%

A new reliability-oriented place and route algorithm for SRAM-based FPGAs

The very high integration levels reached by VLSI technologies for SRAM-based field programmable gate arrays (FPGAs) lead to high occurrence-rate of transient faults induced by single event upsets (SEUs) in FPGAs' configuration memory. Since the configuration memory defines which circuit an SRAM-based FPGA implements, any modification induced by SEUs may dramatically change the implemented circuit. When such devices are used in safety-critical applications, fault-tolerant techniques are needed to mitigate the effects of SEUs in FPGAs' configuration memory. In this paper, we analyze the effects induced by the SEUs in the configuration memory of SRAM-based FPGAs. The reported analysis outlines that SEUs in the FPGA's configuration memory are particularly critical since they are able to escape well-known fault masking techniques such as triple modular redundancy (TMR). We then present a reliability-oriented place and route algorithm that, coupled with TMR, is able to effectively mitigate the effects of the considered faults. The effectiveness of the new reliability-oriented place and route algorithm is demonstrated by extensive fault injection experiments showing that the capability of tolerating SEU effects in the FPGA's configuration memory increases up to 85 times with respect to a standard TMR design technique

Hardening FPGA-based Systems Against SEUs: A New Design Methodology

SRAM-based Field Programmable Gate Arrays (FPGAs) are very susceptible to Single Event Upsets (SEUs) that may have dramatic effects on the circuits they implement. In this paper we present a design flow composed by both standard tools, and ad-hoc developed tools, which designers can use fruitfully for developing circuits resilient to SEUs. Experiments are reported on both benchmarkscircuits and on a realistic circuit to show the capabilities of the proposed design flow.

Defect tolerance in multiple-FPGA systems

SRAM-based field programmable gate arrays (FPGAs) have an inherent capacity for defect tolerance. A simple scheme that exploits this potential in multiple-FPGA systems is proposed. The symmetry of the system is exploited to yield a large number of possible mappings of bitstreams on FPGAs, which results in a high probability that at least one functional mapping exists. It is shown that the behaviour of a system built using a large number of defective FPGAs approaches that of the ideal defect-free system. Various interconnection topologies such as the tree, the crossbar and a hybrid form are compared.

Configuration compression for FPGA-based embedded systems

Field programmable gate arrays (FPGAs) are a promising technology for developing high-performance embedded systems. The density and performance of FPGAs have drastically improved over the past few years. Consequently, the size of the configuration bit-streams has also increased considerably. As a result, the cost-effectiveness of FPGA-based embedded systems is significantly affected by the memory required for storing various FPGA configurations. This paper proposes a novel compression technique that reduces the memory required for storing FPGA configurations and results in high decompression efficiency. Decompression efficiency corresponds to the decompression hardware cost as well as the decompression rate. The proposed technique is applicable to any SRAM-based FPGA device since configuration bit-streams are processed as raw data. The required decompression hardware is simple and the decompression rate scales with the speed of the memory used for storing the configuration bit-streams. Moreover, the time to configure the device is not affected by our compression technique. Using our technique, we demonstrate up to 41% savings in memory for configuration bit-streams of several real-world applications.

Analysis of the robustness of the TMR architecture in SRAM-based FPGAs

Non radiation-hardened SRAM-based Field Programmable Gate Arrays (FPGAs) are very sensitive to Single Event Upsets (SEUs) affecting their configuration memory and thus suitable hardening techniques are needed when they are intended to be deployed in critical applications. Triple Module Redundancy is a known solution for hardening digital logic against SEUs that is widely adopted for traditional techniques (like ASICs). In this paper we present an analysis of the SEU effects in circuits hardened according to the Triple Module Redundancy to investigate the possibilities of successfully applying TMR to designs mapped on commercial-off-the-shelf SRAM-based FPGAs, which are not radiation hardened. We performed different fault-injection experiments in the FPGA configuration memory implementing TMR designs and we observed that the percentage of SEUs escaping TMR could reach 13%. In this paper we report detailed evaluations of the effects of the observed failure rates, and we proposed a first step toward an improved TMR implementation.

Simulation-based analysis of SEU effects in SRAM-based FPGAs

SRAM-based field programmable gate arrays (FPGAs) are particularly sensitive to single event upsets (SEUs) that, by changing the FPGA's configuration memory, may affect dramatically the functions implemented by the device. In This work we describe a new approach for predicting SEU effects in circuits mapped on SRAM-based FPGAs that combines radiation testing with simulation. The former is used to characterize (in terms of device cross section) the technology on which the FPGA device is based, no matter which circuit it implements. The latter is used to predict the probability for a SEU to alter the expect behavior of a given circuit. By combining the two figures, we then compute the cross section of the circuit mapped on the pre-characterized device. Experimental results are presented that compare the approach we developed with a traditional one based on radiation testing only, to measure the cross section of a circuit mapped on an FPGA. The figures here reported confirm the accuracy of our approach.

Errata to “Identification and Classification of Single-Event Upsets in the Configuration Memory of SRAM-Based FPGAs”

This paper presents the radiation testing of a commercial-off-the-shelf SRAM-based field-programmable gate arrays (FPGAs) with heavy ions. Test experiments have been conducted to identify and to classify the single-event upsets (SEUs) in the configuration memory that induce single-event functional interrupt for the user-implemented circuit. Moreover the paper presents a new approach for assessing the effects of SEUs based on the combination of radiation testing and simulation-based fault injection tool. First experimental results show the FPGA look-up table (LUT) resources (used to implement combinatorial logic) are the most sensitive to SEUs, whereas interconnect resources are the most critical for the device cross section because they use the largest number of configuration bits. The analysis of experimental data underlines that the most probable error affecting interconnections is the shorting of two nets. This observation indicates that new fault models should be considered along with the classic stuck-at one model designing fault-tolerant architectures, which are intended for implementation in FPGA devices.

SEU mitigation for half-latches in Xilinx Virtex FPGAs

The performance, in-system reprogrammability, flexibility, and reduced costs of SRAM-based field programmable gate arrays (FPGAs) make them very interesting for high-speed on-orbit data processing, but the current generation of radiation-tolerant SRAM-based FPGAs are based on commercial-off-the-shelf technologies and, consequently, are susceptible to single-event upset effects. In this paper, we discuss in detail the consequences of radiation-induced single-event upsets (SEUs) in the state of half-latch structures found in Xilinx Virtex FPGAs and describe methods for mitigating the effects of half-latch SEUs. One mitigation method's effectiveness is then illustrated through experimental data gathered through proton accelerator testing at Crocker Nuclear Laboratory, University of California-Davis. For the specific design and mitigation methodology tested, the mitigated design demonstrated more than an order of magnitude improvement in reliability over the unmitigated version of the design in regards to average proton fluence until circuit failure.

Identification and classification of single-event upsets in the configuration memory of SRAM-based FPGAs

This paper presents the radiation testing of a commercial-off-the-shelf SRAM-based field-programmable gate arrays (FPGAs) with heavy ions. Test experiments have been conducted to identify and to classify the single-event upsets (SEUs) in the configuration memory that induce single-event functional interrupt for the user-implemented circuit. Moreover the paper presents a new approach for assessing the effects of SEUs based on the combination of radiation testing and simulation-based fault injection tool. First experimental results show the FPGA look-up table (LUT) resources (used to implement combinatorial logic) are the most sensitive to SEUs, whereas interconnect resources are the most critical for the device cross section because they use the largest number of configuration bits. The analysis of experimental data underlines that the most probable error affecting interconnections is the shorting of two nets. This observation indicates that new fault models should be considered along with the classic stuck-at one model designing fault-tolerant architectures, which are intended for implementation in FPGA devices.

Detecting, diagnosing, and tolerating faults in SRAM-based field programmable gate arrays

Topics related to the faults in SRAM-based field programmable gate arrays (FPGAs) have been intensively studied in recent research studies. These topics include FPGA fault detection, FPGA fault dia...

Detecting, diagnosing, and tolerating faults in SRAM-based field programmable gate arrays: a survey

Topics related to the faults in SRAM-based field programmable gate arrays (FPGAs) have been intensively studied in recent research studies. These topics include FPGA fault detection, FPGA fault diagnosis, FPGA defect tolerance, and FPGA fault tolerance. This paper provides a guided tour to the approaches related to these topics. These include techniques, which are applied to the FPGA and others which have been recently introduced and can be applied to today's FPGAs.

The design of an SRAM-based field-programmable gate array. I. Architecture

Field-programmable gate arrays (FPGAs) are now widely used for the implementation of digital systems, and many commercial architectures are available. Although the literature and data books contain detailed descriptions of these architectures, there is very little information on how the high-level architecture was chosen, and no information on the circuit-level or physical design of the devices. This paper describes the high-level architectural design of a static-random-access memory programmable FPGA. A forthcoming Part II will address the circuit design issues through to the physical layout. The logic block and routing architecture of the FPGA was determined through experimentation with benchmark circuits and custom-built computer-aided design tools. The resulting logic block is an asymmetric tree of four-input lookup tables that are hard-wired together and a segmented routing architecture with a carefully chosen segment length distribution.

SRAM-Based FPGAs: Testing the Embedded RAM Modules

This paper addresses the problem of testing the RAM mode of the LUT/RAM modules of configurable SRAM-based Field Programmable Gate Arrays (FPGAs) using a minimum number of test configurations. A model of architecture for the LUT/RAM module with N inputs and 2N memory cells is proposed taking into account the LUT and RAM modes. Targeting the RAM mode, we demonstrate that a unique test configuration is required for a single module. The problem is shown equivalent to the test of a classical SRAM circuit allowing to use existing algorithms such as the March tests. We also propose a unique test configuration called ‘pseudo shift register’ for an m × m array of modules. In the proposed configuration, the circuit operates as a shift register and an adapted version of the MATS++ algorithm called ‘shifted MATS++’ is described.

Educational design of high-performance arithmetic circuits on FPGA

In many courses of digital system design, a large amount of time is spent introducing the students to architectural and circuit design. A typical laboratory application is the design of arithmetic digital circuits. In the past, as a hardware platform for educational digital design, programmable logic arrays (PLAs) have been widely used. Today, the field programmable gate arrays (FPGAs), seem to be the most suitable technology for this purpose. In this paper, among the many possible design examples, the Authors have chosen the implementation of the radix-4 SRT algorithm for division. As convenient trade-off between area cost and performance, SRT division implementation is being used in many recent general-purpose processors. The circuit offers a sufficient complexity to give practice to the students and to stimulate useful classroom discussions. Moreover, a system for rapid circuit prototyping and testing has been carried out. The prototyping-board allows the transfer of student designs into an SRAM-based FPGA chip and the performance of functional tests of the circuit. The prototyping system is directly controlled by a personal computer via ISA-bus and it allows students concentrate their attention on elaborating the digital design rather than striving with board assembly and PC-to-board communication.

Virtual signal processors

The introduction of SRAM-based field programmable gate arrays (FPGAs) has opened up a new dimension to parallel computing architectures. This paper describes an alternative approach to parallel computing — reconfigurable or virtual parallel processing (VPP). Rather than mapping an application onto a given parallel machine, the WP approach synthesizes the appropriate type and number of processing elements, as well as the interconnection topology, that is optimal for the application. For each application, configuration data is downloaded to the machine that personalizes the hardware for the task at hand. The paper provides a brief description of the authors reconfigurable computer, Archimedes. The benefits of the VPP approach are highlighted by two example applications — the 2-D FFT and a narrow-band digital filter. A novel parallel implementation of a polynomial transform based 2-D transform is described and compared with results for distributed memory parallel machines that have been reported in the literature. The comparison highlights the computational advantage provided by reconfigurable computing. The digital filter implementation employs sigma–delta modulation encoding to reduce the arithmetic workload. The application of this technology to a communications receiver is explained.

Some experiments about wave pipelining on FPGA's

Wave pipelining offers a unique combination of high speed, low latency, and moderate power consumption. The construction of wave pipelines is benefited by the use of gates and buffers with data-independent delays and the knowledge of the interconnection delays. These two features are present in several SRAM-based field programmable gate arrays (FPGA's): look-up tables (LUT's) allow the designer to mask the delay of different gates and combinational functions, and the timing characteristics of each wire segment are a priori known. This work describes a set of experiments about wave pipelining on FPGA's. The results show that a 13-LUT logic depth circuit mapped on an XC4005PC84-6 runs as high as 85 MHz (single phase clocking) or 80 MHz (intentionally skewed clocking), exhibiting a latency of 95 ns. This high throughput/latency ratio is unattainable using classic pipelining.