A software controlled voltage tuning system using multi-purpose ring oscillators

TL;DR

This paper introduces a software-controlled voltage tuning system utilizing multi-purpose ring oscillators to adaptively reduce energy consumption in processors without performance loss.

Contribution

It presents a novel method using multi-purpose ROs for voltage tuning based on process and environment variations, demonstrated on XMOS microprocessors.

Findings

Up to 25% dynamic power savings achieved.

No performance reduction or impact on real-time constraints.

Method applicable across devices of the same model.

Abstract

This paper presents a novel software driven voltage tuning method that utilises multi-purpose Ring Oscillators (ROs) to provide process variation and environment sensitive energy reductions. The proposed technique enables voltage tuning based on the observed frequency of the ROs, taken as a representation of the device speed and used to estimate a safe minimum operating voltage at a given core frequency. A conservative linear relationship between RO frequency and silicon speed is used to approximate the critical path of the processor. Using a multi-purpose RO not specifically implemented for critical path characterisation is a unique approach to voltage tuning. The parameters governing the relationship between RO and silicon speed are obtained through the testing of a sample of processors from different wafer regions. These parameters can then be used on all devices of that model. The tuning method and software control framework is demonstrated on a sample of XMOS XS1-U8A-64 embedded microprocessors, yielding a dynamic power saving of up to 25% with no performance reduction and no negative impact on the real-time constraints of the embedded software running on the processor.