GASP-a genetic algorithm for standard cell placement

This paper describes the implementation of the genetic algorithm for standard cell placement, GASP-1. As opposed to simulated annealing, which normally uses pairwise interchange for transforming the layout configuration, in a genetic algorithm, the crossover operator is used to combine two current configurations to generate a new configuration (similar to reproduction in living organisms). The traditional genetic crossover operator, as proposed by Holland (1985), cannot be applied to the cell placement problem without modification, because it occasionally results in illegal placement. A great deal of effort has therefore been directed towards finding an efficient crossover operator for this problem domain. Three powerful crossover operators have been implemented, and their performance in reducing the interconnect length has been compared. The results of this comparison were conclusively in favour of Cycle crossover. Besides crossover, two other genetic operators-mutation and inversion-have been used to improve the efficiency of the search process. In order to benchmark the performance of GASP-1, the best possible compromise of the parameters was picked, and the algorithm was run to place five industrial circuits consisting of 100 to 800 cells. The results were very encouraging