Area Optimization of Multi-Cycle Operators in High-Level Synthesis

Conventional high-level synthesis algorithms usually employ multi-cycle operators to reduce the cycle length in order to improve the circuit performance. These operators need several cycles to execute one operation, but the entire functional unit is not used in any cycle. Additionally, the execution of operations over wider multi-cycle operators is unfeasible if their results must be available in a smaller number of cycles than the functional unit delay. This obliges to add new functional resources to the datapath even if multi-cycle operators are idle when the execution of the operation begins. In this paper a new design technique to overcome the restricted reusability of multi-cycle operators is presented. It reduces the area of these functional units allowing their internal reuse when executing one operation. It also expands the possibilities of common hardware sharing as it allows the partial use of multicycle operators to calculate narrower operations faster than the functional unit delay. This technique is applied as an optimization phase at the end of the high-level synthesis process, and can optimize the circuits synthesized by any high-level synthesis tool