FPGA布线通道分布对面积效率的影响研究

该文提出了现场可编程门阵列(FPGA)布线通道不均匀分布对芯片面积的影响。引入几个典型的数学分布函数(高斯,正弦和三角分布),实现通道容量随函数分布变化的新FPGA结构。将这些结构的FPGA与传统的布线通道均匀分布的FPGA作比较,结果表明按照数学分布变化的布线通道分布结构比均匀分布情况下的面积效率要高。亦即通道分布的变化趋势是峰值位置位于芯片中央,即通道容量最大,从中间位置向边缘按函数变化趋势逐渐变小。     

Speed and area tradeoffs in cluster-based FPGA architectures

One way to reduce the delay and area of field-programmable gate arrays (FPGAs) is to employ logic-cluster-based architectures, where a logic cluster is a group of logic elements connected with high-speed local interconnections. In this paper, we empirically evaluate FPGA architectures with logic clusters ranging in size from 1 to 20, and show that compared to architectures with size 1 clusters, architectures with size 8 clusters have 23% less delay (30% faster clock speed) and require 14% less area. We also show that FPGA architectures with large cluster sizes can significantly reduce design compile time-an increasingly important concern as the logic capacity of FPGA's rises. For example, an architecture that uses size 20 clusters requires seven times less compile time than an architecture with size 1 clusters     

Signal processing at 250 MHz using high-performance FPGA's

This paper describes an application in high-performance signal processing using reconfigurable computing engines: a 250 MHz cross correlator for radio astronomy. Experimental results indicate that complementary metal-oxide-semiconductor (CMOS) field programmable gate arrays (FPGA's) can perform useful computation at 250 MHz. The notion of an “event horizon” for FPGA's leads to clear design constraints for high-speed application developers, and can be applied to a variety of real-time signal processing algorithms. Recent estimates indicate that higher performance FPGA's available early in 1998 can attain speeds of over 300 MHz using 20% fewer logic elements than current designs. The results of this design work provide important clues on how to improve FPGA architectures for signal processing at hundreds of MHz. Direct routing channels between logic elements can significantly increase performance. Routing architectures with four-way symmetry allow for rotations and reflections of subcircuits needed for optimal packing density. Experimental results indicate that clock buffering often limits the top speed of the FPGA. Wave pipelining of the clock distribution network may improve FPGA performance     

Using bus-based connections to improve field-programmable gate-array density for implementing datapath circuits

As the logic capacity of field-programmable gate arrays (FPGAs) increases, they are increasingly being used to implement large arithmetic-intensive applications, which often contain a large proportion of datapath circuits. Since datapath circuits usually consist of regularly structured components (called bit-slices) which are connected together by regularly structured signals (called buses), it is possible to utilize datapath regularity in order to achieve significant area savings through FPGA architectural innovations. This paper describes such an FPGA routing architecture, called the multibit routing architecture, which employs bus-based connections in order to exploit datapath regularity. It is experimentally shown that, compared to conventional FPGA routing architectures, the multibit routing architecture can achieve 14% routing area reduction for implementing datapath circuits, which represents an overall FPGA area savings of 10%. This paper also empirically determines the best values of several important architectural parameters for the new routing architecture including the most area efficient granularity values and the most area efficient proportion of bus-based connections.     

The memory/logic interface in FPGAs with large embedded memoryarrays

As the capacities of field-programmable gate arrays (FPGAs) grow, they will be used to implement much larger circuits than ever before. These larger circuits often require significant amounts of storage. In order to address these storage requirements, FPGAs with large embedded memory arrays are now being developed by several vendors. One of the crucial components of an FPGA with on-chip memory is the routing structure between the memory arrays and logic resources. If this memory/logic interface is not flexible enough, many circuits will be unroutable, while if it is too flexible, it will be slower and consume more chip area than is necessary. In this paper, we show that an interconnect in which each memory pin can connect to between four and seven logic routing tracks is best in terms of both area and speed. We also show that by adding switches to support nets that connect multiple memory arrays, we can reduce the memory access time by up to 25% and improve the routability slightly     

Architecture of field-programmable gate arrays

A survey of field-programmable gate array (FPGA) architectures and the programming technologies used to customize them is presented. Programming technologies are compared on the basis of their volatility, size parasitic capacitance, resistance, and process technology complexity. FPGA architectures are divided into two constituents: logic block architectures and routing architectures. A classification of logic blocks based on their granularity is proposed, and several logic blocks used in commercially available FPGAs are described. A brief review of recent results on the effect of logic block granularity on logic density and performance of an FPGA is then presented. Several commercial routing architectures are described in the context of a general routing architecture model. Finally, recent results on the tradeoff between the flexibility of an FPGA routing architecture, its routability, and its density are reviewed     

Flexibility of interconnection structures for field-programmablegate arrays

The relationship between the routability of a field-programmable gate array (FPGA) and the flexibility of its interconnection structures is examined. The flexibility of an FPGA is determined by the number and distribution of switches used in the interconnection. While good routability can be obtained with a high flexibility, a large number of switches will result in poor performance and logical density because each switch has significant delay and area. The minimum number of switches required to achieve good routability is determined by implementing several industrial circuits in a variety of interconnection architectures. These experiments indicate that high flexibility is essential for the connection block that joins the logic blocks to the routing channel, but a relative low flexibility is sufficient for switch blocks at the junction of horizontal and vertical channels. Furthermore, it is necessary to use only a few more routing tracks than the absolute minimum possible with structures of surprisingly low flexibility     

An architecture for electrically configurable gate arrays

An architecture for electrically configurable gate arrays using a two-terminal antifuse element is described. The architecture is extensible, and can provide a level of integration comparable to mask-programmable gate arrays. This is accomplished by using a conventional gate array organization with rows of logic modules separated by wiring channels. Each channel contains segmented wiring tracks. The overhead needed to program the antifuses is minimized by an addressing scheme that utilizes the wiring segments, pass transistors between adjacent segments, shared control lines, and serial addressing circuitry at the periphery of the array. This circuitry can also be used to test the device prior to programming and observe internal nodes after programming. By providing sufficient wiring tracks segmented into carefully chosen lengths and a logic module with a high degree of symmetry, fully automated placement and routing is facilitated     

基于测试系统的FPGA逻辑资源的测试

FPGA在许多领域已经得到广泛应用,其测试问题也显得越来越突出。文章针对基于SRAM结构FPGA的特点,以Xilinx公司的XC4000系列芯片为例,利用检测可编程逻辑资源的多逻辑单元(CLB)混合故障的测试方法,阐述了如何在BC3192V50测试系统上实现FPGA的在线配置以及功能和参数测试。它是一种基于测试系统的通用的FPGA配置和测试方法。     

An efficient logic emulation system

The Realizer, is a logic emulation system that automatically configures a network of field-programmable gate arrays (FPGAs) to implement large digital logic designs, is presented. Logic and interconnect are separated to achieve optimum FPGA utilization. Its interconnection architecture, called the partial crossbar, greatly reduces system-level placement and routing complexity, achieves bounded interconnect delay, scales linearly with pin count, and allows hierarchical expansion to systems with hundreds of thousands of FPGA devices in a fast and uniform way. An actual multiboard system has been built, using 42 Xilinx XC3090 FPGAs for logic. Several designs, including a 32-b CPU datapath, have been automatically realized and operated at speed. They demonstrate very good FPGA utilization. The Realizer has applications in logic verification and prototyping, simulation, architecture development, and special-purpose execution     

The Triptych FPGA architecture

Field-programmable gate arrays (FPGAs) are an important implementation medium for digital logic. Unfortunately, they currently suffer from poor silicon area utilization due to routing constraints. In this paper we present Triptych, an FPGA architecture designed to achieve improved logic density with competitive performance. This is done by allowing a per-mapping tradeoff between logic and routing resources, and with a routing scheme designed to match the structure of typical circuits. We show that, using manual placement, this architecture yields a logic density improvement of up to a factor of 3.5 over commercial FPGAs, with comparable performance. We also describe Montage, the first FPGA architecture to fully support asynchronous and synchronous interface circuits     

The Transmogrifier-2: a 1 million gate rapid-prototyping system

This paper describes the Transmogrifier-2 (TM-2), a second-generation multifield programmable gate array (FPGA) rapid-prototyping system. The largest version of the system will comprise 16 boards that each contain two Altera 10K50 FPGA's, four I-Cube interconnect chips, and up to 8 Mbytes of memory. The inter-FPGA routing architecture of the TM-2 uses a novel interconnect structure, a nonuniform partial crossbar, that provides a constant delay between any two FPGA's in the system. The TM-2 architecture is modular and scalable, meaning that systems of various sizes can be constructed from copies of the same board, while maintaining routability and the constant delay feature. Other features include a system-level programmable clock that allows single-cycle access to off-chip memory, and programmable clock waveforms with edge resolution of 10 ns. The first Transmogrifier-2 boards have been manufactured and are functional. They have recently been used successfully in some simple graphics acceleration applications     

Antifuse field programmable gate arrays

An antifuse is an electrically programmable two-terminal device with small area and low parasitic resistance and capacitance. Field-programmable gate arrays (FPGAs) using antifuses in a segmented channel routing architecture now offer the digital logic capabilities of an 8000-gate conventional gate array and system speeds of 40-60 MHz. A brief survey of antifuse technologies is provided. the antifuse technology, routing architecture, logic module, design automation, programming, testing and use of ACT antifuse FPGAs are described. Some inherent tradeoffs involving the antifuse characteristics, routing architecture and logic module are illustrated     

Testing configurable LUT-based FPGA's

We present a new technique for testing field programmable gate arrays (FPGA's) based on look-up tables (LUT's). We consider a generalized structure for the basic FPGA logic element (cell); it includes devices such as LUT's, sequential elements (flip-flops), multiplexers and control circuitry. We use a hybrid fault model for these devices. The model is based on a physical as well as a behavioral characterization. This permits detection of all single faults (either stuck-at or functional) and some multiple faults using repeated FPGA reprogramming. We show that different arrangements of disjoint one-dimensional (l-D) cell arrays with cascaded horizontal connections and common vertical input lines provide a good logic testing regimen. The testing time is independent of the number of cells in the array (C-testability), We define new conditions for C-testability of programmable/reconfigurable arrays. These conditions do not suffer from limited I/O pins. Cell configuration affects the controllability/observability of the iterative array. We apply the approach to various Xilinx FPGA families and compare it to prior work     

Optimised bit serial modular multiplier for implementation on fieldprogrammable gate arrays

A high-speed architecture for bit serial modular multiplication is presented. The design of this array is highly regular, allowing the specific logic and routing resources available in field programmable gate arrays (FPGAs) to be exploited. Furthermore, an optimised array is presented which exploits the reprogrammability of the FPGA, such that a longer bit length can be implemented on the same FPGA     

Placement and routing tools for the Triptych FPGA

Field-programmable gate arrays (FPGAs) are becoming an increasingly important implementation medium for digital logic. One of the most important keys to using FPGAs effectively is a complete, automated software system for mapping onto the FPGA architecture. Unfortunately, many of the tools necessary require different techniques than traditional circuit implementation options, and these techniques are often developed specifically for only a single FPGA architecture. In this paper we describe automatic mapping tools for Triptych, an FPGA architecture with improved logic density and performance over commercial FPGAs. These tools include a simulated-annealing placement algorithm that handles the routability issues of fine-grained FPGAs, and an architecture-adaptive routing algorithm that can easily be retargeted to other FPGAs. We also describe extensions to these algorithms for mapping asynchronous circuits to Montage, the first FPGA architecture to completely support asynchronous and synchronous interface applications     

Hierarchical interconnection structures for field programmable gatearrays

Field programmable gate arrays (FPGA's) suffer from lower density and lower performance than conventional gate arrays. Hierarchical interconnection structures for field programmable gate arrays are proposed. They help overcome these problems. Logic blocks in a field programmable gate array are grouped into clusters. Clusters are then recursively grouped together. To obtain the optimal hierarchical structure with high performance and high density, various hierarchical structures with the same routability are discussed. The field programmable gate arrays with new architecture can be efficiently configured with existing computer aided design algorithms. The k-way min-cut algorithm is applicable to the placement step in the implementation. Global routing paths in a field programmable gate array can be obtained easily. The placement and global routing steps can be performed simultaneously. Experiments on benchmark circuits show that density and performance are significantly improved     

The yield enhancement of field-programmable gate arrays

The fine granularity and reconfigurable nature of field-programmable gate arrays (FPGA's) suggest that defect-tolerant methods can be readily applied to these devices in order to increase their maximum economic sizes, through increased yield. This paper identifies the inability to contain faults within single cells and the need for fast reconfiguration as the key obstacles to obtaining a significant increase in yield. Monte Carlo defect modeling of the photolithographic layers of VLSI FPGA's is used as a foundation for the yield modeling of various defect-tolerant architectures. Results suggest that a medium-grain architecture is the best solution, offering a substantial increase in size without significant side effects. This architecture is shown to produce greater gate densities than the alternative approach of realizing ultralarge scale FPGA's-multichip modules