VLSI placement with pre-placed modules based on less flexibility first principles

The locations of ROM, RAM, and CPU often were required to fix a priori while other modules are subject to be placed in the rest of the chip area. These situations were formulated as placement with pre-placed modules. Rectilinear substrate and holes of the substrate can be also modeled with the use of pre-placed modules. Unlike the coding scheme based stochastic optimization placement algorithms, which need special feasible checking of the representation for placement with pre-placed modules, we develop a new deterministic algorithm to cope with the same problem. The placement area is evaluated first. Then the flexibility of each placement module is calculated according to its packing location, size and connectivity among other neighbor modules. According to the less flexibility first principle, the placement is completed through a recursive packing process. Pre-placed modules just form the placement area, no extra calculation is needed. Experiment results show our algorithm is better than stochastic algorithm