The current status of VLSI layout and directions for future research are addressed, with emphasis on the authors' own work Necessary terminology and definitions and, whenever possible, a precise formulation of the problems are provided Placement and floorplanning for both the sea-of-gates and building-block designs are examined The former emphasizes the connectivity specification, whereas the latter must also consider module shape and size Global routing based on a method of successive cuts on a chip is discussed This is a hierarchical top-down approach that is useful for both of the above designs A two-dimensional detailed routing problem and the rip-up and rerouting problem are also discussed The field of computational geometry and its application to layout-in particular, to gridless routing and compaction-are reviewed, and layout engines are considered >

Recent advances in VLSI layout

This paper describes a new design for a hardware accelerator to support grid-based Maze Routing. Based on the direct mapped approach of Breuer and Shamsa [3], this work refines their design to substantially reduce the hardware requirements of each processing element while at the same time adding support for mulitilayer routing and fast iterative routing. An RTL implementation has been developed for this design in VHDL, and initial results show promise for its realization using ASIC, custom, or FPGA technology.

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A new look at hardware maze routing

A new parallel hierarchical algorithm for global routing (PHIGURE) is presented. The router is based on the work of M. Burstein and R. Pelavin, (IEEE Trans. CAD, vol.CAD-2, no.4, p.223-34, Oct. 1983) but has many extensions for general global routing and parallel execution. Main features of the algorithm include structured hierarchical decomposition into separate independent tasks which are suitable for parallel execution and adaptive simplex solution for adding feedthroughs and adjusting channel heights for row-based layout. The algorithm is described and results are presented for a shared-memory multiprocessor implementation. >

PHIGURE: a parallel hierarchical global router

The authors describe their experience and progress in accelerating an FPGA router. Placement and routing is undoubtedly the most time-consuming process in automatic chip design or configuring programmable logic devices as reconfigurable computing elements. Their goal is to accelerate routing of FPGAs by 10 fold with a combination of processor clusters and hardware acceleration. Coarse-grain parallelism is exploited by having several processors route separate groups of nets in parallel. A hardware accelerator is presented which exploits the fine-grain parallelism in routing individual nets.

Acceleration of an FPGA router

FPGA place and route is time consuming, often serving as the major obstacle inhibiting a fast edit-compile-test loop in prototyping and development and the major obstacle preventing late-bound hardware and design mapping for reconfigurable systems. Previous work showed that hardware-assisted routing can accelerate fanout-free routing on Fat-Trees by three orders of magnitude with modest modifications to the network itself. In this paper, we show how these techniques can be applied to any FPGA and how they can be implemented on top of LUT networks in cases where modification of the FPGA itself is not justified. We further show how to accommodate fanout and how to achieve comparable route quality to software-based methods. For a tree network, we estimate an FPGA implementation of our routing logic could route the Toronto Place and Route Benchmarks at least two orders of magnitude faster than a software Pathfinder while achieving within 3% of the aggregate quality. Preliminary results on small mesh benchmarks achieve within one track of vpr-fast.

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Stochastic, spatial routing for hypergraphs, trees, and meshes

A new parallel-processing wire-routing algorithm is presented and implemented on a parallel processor. The two main features of the parallel algorithm are the control of the path quality and the finding of a quasi-minimum Steiner tree. Both Lee's maze algorithm and the proposed algorithm are implemented on an AAP-1 two-dimensional array processor, and the performance is compared to that of software programming on a general-purpose computer. It is shown experimentally that routing by the proposed algorithm implemented on the AAP-1 is 230 times faster than a software maze router run on a 1-MIPS computer for a three-pin/net circuit on a 256 X 256 grid.

Y. Sugiyama

Papers

A Parallel Adaptable Routing Algorithm and its Implementation on a Two-Dimensional Array Processor