Automatic selection of instruction op-codes of low-power core processors

A methodology is presented for automatically determining an assignment of instruction op-codes that guarantees the minimisation of bit transitions occurring inside the registers of the pipeline stages involved in instruction fetching and decoding. The assignment of the binary patterns to the op-codes is driven by the statistics concerning instruction adjacency collected through instruction-level simulation of typical software applications. Therefore the technique is best exploited when applied to encode the instruction set of core processors and microcontrollers, since components of these types are commonly used to execute fixed portions of machine code within embedded systems. The effectiveness of the methodology is illustrated through experimental data obtained on a realistic case study, namely, the MIPS R4000 RISC microprocessor