An Efficient Multi-Output LUT Mapping Technique for Field-Programmable Gate Arrays

The use of multi-output look-up tables (LUTs) is a widely adopted approach in contemporary commercial field-programmable gate arrays (FPGAs). Larger LUT configurations (e.g., six-input LUTs) can be partitioned into smaller LUTs (e.g., two five-input LUTs, maintaining a total input count of less than six). This capability of generating a second output from a larger LUT is not only crucial for reducing logic cell count and enhancing the utilization efficiency of logic resources—thus conserving area—but also plays a key role in optimizing system-level delays and energy consumption. In this paper, we propose an efficient multi-output LUT mapping technique, incorporating several highly efficient technology mapping algorithms, which focus on optimizing the mapping from an interconnection perspective as alternatives to directly merging smaller LUTs. These algorithms include a side-fanout insertion algorithm, and a runtime multi-output cut generation algorithm. The proposed methods improve mapping efficiency and enhance performance. The benchmarking results demonstrate that the dual-output mapping algorithms achieve LUT area reductions of up to 35% and 6%, compared to the state-of-the-art ABC six-input, single-output LUT mapping technique and previous work focusing on dual-output LUT mapping techniques that optimize cut generation parameters. Moreover, FPGA system-level simulations also show that area, delay, and energy can all be optimized based on this multi-output mapping technique.