Design of asynchronous function unit and software development tools for a low-power DSP

The requirement for extended battery life, reduced size and low electromagnetic interference (EMI) for mobile communication equipment has led to the development of a novel low-power asynchronous digital signal processor (DSP) device known as CADRE (configurable asynchronous DSP for reduced energy). The architecture of CADRE is based on an asynchronous ‘function unit’ (FU) which has been designed to reduce power consumption as far as possible without sacrificing speed. This paper describes current work in redesigning the FU hardware to achieve improvements in power efficiency with the use of pass-transistor logic, voltage scaling and modifications to the hardware multiplication and addition circuitry. Software support for the new DSP is needed to avoid manual assembly-level programming and a ‘C’ compiler is being developed to make the best use of the power saving features of CADRE when implementing speech coding algorithms as required by 3G mobile telephony. A cost database and ‘pattern’ program for guiding the energy aware compilation is used and three optimisation strategies are described. Results are presented which demonstrate the effectiveness of the optimisations.