A high-level model of embedded flash energy consumption

James Pallister, Kerstin Eder, Simon J. Hollis, Jeremy Bennett

The alignment of code in the flash memory of deeply embedded SoCs can have a large impact on the total energy consumption of a computation. We investigate the effect of code alignment in six SoCs and find that a large proportion of this energy (up to 15% of total SoC energy consumption) can be saved by changes to the alignment. A flexible model is created to predict the read-access energy consumption of flash memory on deeply embedded SoCs, where code is executed in place. This model uses the instruction level memory accesses performed by the processor to calculate the flash energy consumption of a sequence of instructions. We derive the model parameters for five SoCs and validate them. The error is as low as 5%, with a 11% average normalized RMS deviation overall. The scope for using this model to optimize code alignment is explored across a range of benchmarks and SoCs. Analysis shows that over 30% of loops can be better aligned. This can significantly reduce energy while increasing code size by less than 4%. We conclude that this effect has potential as an effective optimization, saving significant energy in deeply embedded SoCs.

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