Incremental reconfiguration of multi-FPGA systems

In reconfigurable computing, circuits implemented on multi-FPGA systems have to be incrementally modified. Since reconfiguring an FPGA is time-consuming, the time for reconfiguration depends on the number of FPGAs to be reconfigured. Our objective is to reduce the number of such FPGAs. In this paper, we consider the specific problem of incrementally reconfiguring a multi-FPGA system that utilizes the direct interconnection architecture, where routing connections between FPGAs are to neighbors that are near. This problem can be divided into a net addition problem and a net deletion problem. We show that the net addition problem is a generalization of the NP-complete Steiner tree problem. Our algorithm for this problem is based on an adaptation of the Klein-Ravi approximation algorithm for the node-weighted Steiner tree problem. As for the net deletion problem, we prove that it is NP-complete but the problem is solvable in polynomial time for tree topologies. Based on the algorithm for trees, we design an effective heuristic algorithm for the general net deletion problem. Finally, we present an algorithm for solving the incremental reconfiguration problem which handles both placement of new gates and inter-FPGA routing.