Implementing low-power configurable processors - practical options and tradeoffs

Configurable processors enable dramatic gains in energy efficiency, relative to traditional fixed instruction-set processors. This energy advantage comes from three improvements. First, configuration of the instruction set permits a much closer fit of the processor to the target applications, reducing the number of execution cycles required. Second, configuring the processor removes unneeded features, reducing power and area overhead. Third, automatic processor generation tools enable logic optimization, signal switching reductions, and seamless mapping into low-voltage circuits and processes, for very low-power operation. The first improvement has been well-studied. Analysis of the second and third improvements requires detailed circuit and layout experiments, which is the primary focus of this paper. Starting from a range of existing available power saving options, this work explores the tradeoff and analyzes the results: the design priority tradeoff, the process technology impact, and implementing low-power configurable processor using commercial scaled-VDD cell libraries compatible with mainstream SOC practices. These real processor designs can achieve power dissipation approaching 20μW/MHz at 0.8V and close to 10μW/MHz at 0.6V, using production 0.13μm libraries. Finally, this work quantifies the dramatic process, voltage and temperature dependence in post-layout leakage power for small processor designs.