Low-power Processor Design

Power has become an important aspect in the design of general purpose processors. This thesis explores how design tradeoffs affect the power and performance of the processor. Scaling the technology is an attractive way to improve the energy efficiency of the processor. In a scaled technology a processor would dissipate less power for the same performance or higher performance for the same power. Some microarchitectural changes, such as pipelining and caching, can significantly improve efficiency. Unfortunately many other architectural tradeoffs leave efficiency unchanged. This is because a large fraction of the energy is dissipated in essential functions and is unaffected by the internal organization of the processor. Another attractive technique for reducing power dissipation is scaling the supply and threshold voltages. Unfortunately this makes the processor more sensitive to variations in process and operating conditions. Design margins must increase to guarantee operation, which reduces the efficiency of the processor. One way to shrink these design margins is to use feedback control to regulate the supply and threshold voltages thus reducing the design margins. Adaptive techniques can also be used to dynamically trade excess performance for lower power. This results in lower average power and therefore longer battery life. Improvements are limited, however, by the energy dissipation of the rest of the system.