An FPGA layout reconfiguration algorithm based on global routes for engineering changes in system design specifications

Rapid system prototyping is one of the main applications for field-programmable gate arrays (FPGAs). At the stage of rapid system prototyping, design specifications can often be changed since they cannot be determined completely. In this paper, layout design change is focused on and a layout reconfiguration algorithm is proposed for FPGAs. The target FPGA architecture is developed for transport processing. In order to implement more various circuits flexibly, it has three-input lookup tables (LUTs) as minimum logic cells. Since its logic granularity is finer than that of conventional FPGAs, it requires more routing resources to connect them and minimization of routing congestion is indispensable. In layout reconfiguration, the main problem is to add LUTs to initial layouts. Our algorithm consists of two steps: For given placement and global routing of LUTs, in Step 1 an added LUT is placed with allowing that the position of the added LUT may overlap that of a preplaced LUT; Then in Step 2 preplaced LUTs are moved to their adjacent positions so that the overlap of the LUT positions can be resolved. Global routes are updated corresponding to reconfiguration of placement. The algorithm keeps routing congestion small by evaluating global routes directly both in Steps 1 and 2. Especially in Step 2, if the minimum number of preplaced LUTs are moved to their adjacent positions, our algorithm minimizes routing congestion. Experimental results demonstrate that, if the number of added LUTs is at most 20% of the number of initial LUTs, our algorithm generates the reconfigured layouts whose routing congestion is as small as that obtained by executing a conventional placement and global routing algorithm. Run time of our algorithm is within approximately one second.