A practical approach to multiple-class retiming

Retiming is an optimization technique for synchronous circuits introduced by Leiserson and Saxe in 1983. Although powerful, retiming is not very widely used because it does not handle in a satisfying way circuits whose registers have load enable, synchronous and asynchronous set/clear inputs. We propose an extension of retiming whose basis is the characterization of registers into register classes. The new approach called multiple-class retiming handles circuits with an arbitrary number of register classes. We present results on a set of industrial FPGA designs showing the effectiveness and efficiency of multiple-class retiming.