Energy-efficient processing

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DocID17369 Rev 2

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Energy-efficient processing

The STM32L1 is built around the Cortex-M3, an industry standard 32-bit core, which has

been designed, among other criteria, for low power applications. The Cortex-M3 offers a

class-leading performance and code density. Although performance is not naturally linked

with low current consumption, it is a key benefit for most of the low power applications which

have to wake up periodically to execute software tasks. In this case, the Cortex-M3 spends

less time in Run mode due to its processing performance, thus maximizing the time in deep

sleep mode. If we consider only the processing consumption, expressed in mA/DMIPS

(DMIPS standing for Dhrystone MIPS measured using the public benchmark Rev 2.0), the

performance of the Cortex M3 is significantly better than that of the other architectures, in

particular 16-bit microcontrollers.

The performance in DMIPS/MHz being given by the core and its memory interface, the

processing consumption in mA/DMIPS can be maximized using voltage scaling. This

method, also called undervolting, consists of adapting dynamically the supply voltage of the

internal logic with the operating frequency. The STM32L1xx offers three dynamically

selectable voltage ranges, as summarized in the following figure, from 1.8 V (range 1) down

to 1.2 V (range 3), which offers a gain of more than 25% in terms of consumption.