Instruction Subsetting: Trading Power for Programmability

Power consumption is an increasingly important consideration in the design of mixed hardware/software systems. This work defines the notion of instruction subsetting and explores its use as a means of reducing power consumption from the system level of design. Instruction subsetting is defined as creating an application specific instruction set processor from a more general processor, such as a DSP. Although not as effective as an ASIC solution, instruction subsetting provides much of the power savings while maintaining some level of programmability. Instruction set choice strongly affects the savings. We synthesized 5 ASIPs through place and route and found that a poorly chosen instruction set may consume more than 4 times the energy of an ASIP with a proper instruction set choice. This finding will allow designers to consider another set of trade-offs in their hardware/software design space exploration.