IEEE transactions on computer-aided design of integrated circuits and systems : a publication of the IEEE Circuits and Systems Society

The main characteristic of Reconfigurable Computing is the presence of hardware that can be reconfigured to implement specific functionality more suitable for specially tailored hardware than on a simple uniprocessor. Reconfigurable computing systems join microprocessors and programmable hardware in order to take advantage of the combined strengths of hardware and software and have been used in applications ranging from embedded systems to high performance computing. Many of the fundamental theories have been identified and used by the Hardware/Software Co-Design research field. Although the same background ideas are shared in both areas, they have different goals and use different approaches.This book is intended as an introduction to the entire range of issues important to reconfigurable computing, using FPGAs as the context, or "computing vehicles" to implement this powerful technology. It will take a reader with a background in the basics of digital design and software programming and provide them with the knowledge needed to be an effective designer or researcher in this rapidly evolving field.

· Treatment of FPGAs as computing vehicles rather than glue-logic or ASIC substitutes
· Views of FPGA programming beyond Verilog/VHDL
· Broad set of case studies demonstrating how to use FPGAs in novel and efficient ways

Reconfigurable Computing: The Theory and Practice of FPGA-Based Computation

Field-Programmable Gate Arrays (FPGAs) have become one of the key digital circuit implementation media over the last decade. A crucial part of their creation lies in their architecture, which governs the nature of their programmable logic functionality and their programmable interconnect. FPGA architecture has a dramatic effect on the quality of the final device's speed performance, area efficiency, and power consumption. This survey reviews the historical development of programmable logic devices, the fundamental programming technologies that the programmability is built on, and then describes the basic understandings gleaned from research on architectures. We include a survey of the key elements of modern commercial FPGA architecture, and look toward future trends in the field.

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FPGA Architecture: Survey and Challenges

As the technology progresses, interconnect delays have become bottlenecks of chip performance. 3D integrated circuits are proposed as one way to address this problem. However, thermal problem is a critical challenge for 3D IC circuit design. We propose a thermal-driven 3D floorplanning algorithm. Our contributions include: (1) a new 3D floorplan representation, CBA and new interlayer local operations to more efficiently exploit the solution space; (2) an efficient thermal-driven 3D floorplanning algorithm with an integrated compact resistive network thermal model (CBA-T); (3) two fast thermal-driven 3D floorplanning algorithms using two different thermal models with different runtime and quality (CBA-T-Fast and CBA-T-Hybrid). Our experiments show that the proposed 3D floorplan algorithm with CBA representation can reduce the wirelength by 29% compared with a recent published result from (Hsiu et al., 2004). In addition, compared to a nonthermal-driven 3D floorplanning algorithm, the thermal-driven 3D floorplanning algorithm can reduce the maximum on-chip temperature by 56%.

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A thermal-driven floorplanning algorithm for 3D ICs

Classical floorplanning minimizes a linear combination of area and wirelength. When simulated annealing is used, e.g., with the sequence pair representation, the typical choice of moves is fairly straightforward. In this paper, we study the fixed-outline floorplan formulation that is more relevant to hierarchical design style and is justified for very large ASICs and SoCs. We empirically show that instances of the fixed-outline floorplan problem are significantly harder than related instances of classical floorplan problems. We suggest new objective functions to drive simulated annealing and new types of moves that better guide local search in the new context. Wirelength improvements and optimization of aspect ratios of soft blocks are explicitly addressed by these techniques. Our proposed moves are based on the notion of floorplan slack. The proposed slack computation can be implemented with all existing algorithms to evaluate sequence pairs, of which we use the simplest, yet semantically indistinguishable from the fastest reported . A similar slack computation is possible with many other floorplan representations. In all cases the computation time approximately doubles. Our empirical evaluation is based on a new floorplanner implementation Parquet-1 that can operate in both outline-free and fixed-outline modes. We use Parquet-1 to floorplan a design, with approximately 32000 cells, in 37 min using a top-down, hierarchical paradigm.

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Fixed-outline floorplanning: enabling hierarchical design

In this paper, we propose a transitive closure graph-based representation for general floorplans, called TCG, and show its superior properties. TCG combines the advantages of popular representations such as sequence pair, BSG, and B*-tree. Like sequence pair and BSG, but unlike O-tree, B*-tree, and CBL, TCG is P-admissible. Like B*-tree, but unlike sequence pair, BSG, O-tree, and CBL, TCG does not need to construct additional constraint graphs for the cost evaluation during packing, implying faster runtime. Further, TCG supports incremental update during operations and keeps the information of boundary modules as well as the shapes and the relative positions of modules in the representation. More importantly, the geometric relation among modules is transparent not only to the TCG representation but also to its operations, facilitating the convergence to a desired solution. All these properties make TCG an effective and flexible representation for handling the general floorplan/placement design problems with various constraints. Experimental results show the promise of TCG.

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TCG: a transitive closure graph-based representation for non-slicing floorplans

Power has become a burning issue in modern VLSI design. In modern integrated circuits, the power consumed by clocking gradually takes a dominant part. Given a design, we can reduce its power consumption by replacing some flip-flops with fewer multi-bit flip-flops. However, this procedure may affect the performance of the original circuit. Hence, the flip-flop replacement without timing and placement capacity constraints violation becomes a quite complex problem. To deal with the difficulty efficiently, we have proposed several techniques. First, we perform a co-ordinate transformation to identify those flip-flops that can be merged and their legal regions. Besides, we show how to build a combination table to enumerate possible combinations of flip-flops provided by a library. Finally, we use a hierarchical way to merge flip-flops. Besides power reduction, the objective of minimizing the total wirelength is also considered. The time complexity of our algorithm is Θ(n1.12) less than the empirical complexity of Θ(n2). According to the experimental results, our algorithm significantly reduces clock power by 20-30% and the running time is very short. In the largest test case, which contains 1 700 000 flip-flops, our algorithm only takes about 5 min to replace flip-flops and the power reduction can achieve 21%.

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Effective and Efficient Approach for Power Reduction by Using Multi-Bit Flip-Flops

In this brief, we introduce the concept of the P*-admissible representation and propose a P*-admissible, transitive closure graph-based representation for general floorplans, called transitive closure graph (TCG), and show its superior properties. TCG combines the advantages of popular representations such as sequence pair, BSG, and B*-tree. Like sequence pair and BSG, but unlike O-tree, B*-tree, and CBL, TCG is P*-admissible. Like B*-tree, but unlike sequence pair, BSG, O-tree, and CBL, TCG does not need to construct additional constraint graphs for the cost evaluation during packing, implying a faster runtime. Further, TCG supports incremental update during operations and keeps the information of boundary modules as well as the shapes and the relative positions of modules in the representation. More importantly, the geometric relation among modules is transparent not only to the TCG representation but also to its operation, facilitating the convergence to a desired solution. All of these properties make TCG an effective and flexible representation for handling the general floorplan/placement design problems with various constraints. Experimental results show the promise of TCG.

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TCG: A transitive closure graph-based representation for general floorplans

Floorplanning/placement allocates a set of modules into a chip so that no two modules overlap and some specified objective is optimized. To facilitate floorplanning/placement, we need to develop an efficient and effective representation to model the geometric relationship among modules. In this paper, we present a P-admissible representation, called corner sequence (CS), for nonslicing floorplans. CS consists of two tuples that denote the packing sequence of modules and the corners to which the modules are placed. CS is very effective and simple for implementation. Also, it supports incremental update during packing. In particular, it induces a generic worst case linear-time packing scheme that can also be applied to other representations. Experimental results show that CS achieves very promising results for a set of commonly used MCNC benchmark circuits.

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Corner sequence - a P-admissible floorplan representation with a worst case linear-time packing scheme

We extend in this paper the concept of the P-admissible floorplan representation to that of the P*-admissible one. A P*-admissible representation can model the most general floorplans. Each of the currently existing P*-admissible representations, SP, BSG, and TCG, has its strengths as well as weaknesses. We show the equivalence of the two most promising P*-admissible representations, TCG and SP, and integrate TCG with a packing sequence (part of SP) into a new representation, called TCG-S. TCG-S combines the advantages of SP and TCG and at the same time eliminates their disadvantages. With the property of SP, faster packing and perturbation schemes are possible. Inherited nice properties from TCG, the geometric relations among modules are transparent to TCG-S (implying faster convergence to a desired solution), placement with position constraints becomes much easier, and incremental update for cost evaluation can be realized. These nice properties make TCG-S a superior representation which exhibits an elegant solution structure to facilitate the search for a desired floorplan/placement. Extensive experiments show that TCG-S results in the best area utilization, wirelength optimization, convergence speed, and stability among existing works and is very flexible in handling placement with special constraints.

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Jai-Ming Lin

Papers

TCG: a transitive closure graph-based representation for non-slicing floorplans

Effective and Efficient Approach for Power Reduction by Using Multi-Bit Flip-Flops

TCG: A transitive closure graph-based representation for general floorplans

Corner sequence - a P-admissible floorplan representation with a worst case linear-time packing scheme

TCG-S: orthogonal coupling of P*-admissible representations for general floorplans