Energy efficient computing in a DSP has become an important research issue in order to have a longer battery operating time to support the modern portable devices. The energy efficient functional unit has been designed and implemented for an in-house asynchronous DSP named, Configurable Asynchronous DSP for Reduced Energy (CADRE). CADRE-successor (CADRE-s) has been implemented as a full custom design and simulations are presented to successfully demonstrate the energy-efficiency of the FU. The results show that the FU designed can achieve an energy improvement by a factor of 5 in the multiply accumulator units and a factor of nearly 2 for the overall system compared with the original CADRE system.