Dynamic Access Control of Instruction Buses by Using Active Bits Detection for Low Power Systems

Abstract External buses consume substantial power for their high capacitances of bus lines and I/O pins. In this paper, we reduce redundant dynamic power consumption on instruction buses. For expressing a small number, we need the small number of bits (the minimum bits are defined as active bits). But all bit lines on an instruction bus change their status and re-dundant power is consumed. Suppressing switching activity of inactive bits, we can reduce redundant power consumption. Since the active bits are different each data, we reduce power by dynamic analysis and control of the instruction buses. An instruction is constructed of several fields which indicate kinds of operations, register numbers and an immediate value. After analyzing the characteristics of active bits in each field by profiling we change opcode and register assignments by using vari-able length coding to reduce active bits. We achieve more efficient power reduction by using active bits with the code assign-ment of instruction sets. Experimental results illustrate up to 29.1 % switching activity reduction for MPEG2