Instantaneous current modeling in a complex VLIW processor core

Abstract

Measuring and modeling instantaneous current consumption or current dynamics of a processor is important in embedded system designs, wireless communications, low-energy mobile computing, security of communications, and reliability. In this paper, we introduce a new instruction-level based macromodeling approach for instantaneous current consumption in a complex processor core along with new instantaneous current measurement techniques at the instruction and program level. Current consumption and voltage supply waveforms of a processor core were acquired by a sampling oscilloscope through an external interrupt-based setup. Accurate measurements of current, power and energy consumption at the instruction, block, or program level were obtained from analyzing the stored current and voltage waveforms. The current simulation methodology uses elementary functions called atomic functions to approximate the instantaneous current consumption at the instruction level. Based on these atomic functions, a simulated instantaneous current waveform at the program level was built. First, a base waveform of the current simulation was generated by the use of four basic current superposition principles. Secondly, a final waveform of the simulated current was generated from the base waveform by applying a factorial adjustment as a function of the instruction parallelism and sequencing. Step-by-step modeling procedures with numerical examples are presented. The model captured 98% of the variation of the instantaneous current for six complex applications, with an average RMS error of less than 2.2% of the average measured mean. Energy estimates obtained by the use of the simulated current waveforms were within 1.4% of the measured values. This research is important, since for the first time highly accurate instruction-based models of instantaneous current and power for complex processor cores have been developed.