Pipelined compressor tree optimization using integer linear programming

Abstract

Compressor trees offer an effective realization of the multiple input addition needed by many arithmetic operations. However, mapping the commonly used carry save adders (CSA) of classical compressor trees to FPGAs suffers from a poor resource utilization. This can be enhanced by using generalized performance counters (GPCs). Prior work has shown that high efficient GPCs can be constructed by exploiting the low-level structure of the FPGA. However, due to their irregular shape, the selection of those is not straight forward. Furthermore, the compressor tree has to be pipelined to achieve the potential FPGA performance. Then, a selection between registered GPCs or flip-flops has to be done to balance the pipeline. This work defines the pipelined compressor tree synthesis as an optimization problem and proposes a (resource) optimal method using integer linear programming (ILP). Besides that, two new GPC mappings with high efficiency are proposed for Xilinx FPGAs.