Reducing display power to extend mobile battery life

April 10, 2013 //By Pawel Duc, Damian Modrzyk and Aris Aristodemou
Reducing display power to extend mobile battery life
Pawel Duc and Damian Modrzyk, Evatronix together with Aris Aristodemou, ARM examine how reducing display power is able to extend mobile battery life.  

One thing all of us miss when remembering old days of mobile phones is their battery life. As a happy owner of a Nokia 6210, I could afford forgetting a charger for a week of holiday. Of course, the roaming charges back then helped to save battery, but no one will argue the power consumption of today’s mobile devices has grown to become their greatest drawback.

There are many factors that affect the device’s power efficiency, which can be expressed in the number of hours between battery charges. Today, in the era of HD mobile screens there are two major issues that contribute to high battery drain – display brightness and power dissipation in the video and graphics subsystem. In this paper, we will discuss the latter one – smart video and display pipeline in the system-on-chip. Smart, which means providing similar performance to competitive solutions, but requiring much less power.

Challenges for video and graphics subsystems

The modern graphics SoC is required to render high resolutions at high frame rates, and above that perform multiple image post-processing tasks like scaling, rotation, pixel format conversion and others. The typical approach to this challenge is to employ a Graphics Processing Unit (GPU), however, due to its general purpose architecture the power efficiency during specific display processing operations is not optimal.

For such cases, Evatronix developed the PANTA DP IP cores, a family of display processors to take over these display specific tasks from the GPU and thus reduce the power dissipation significantly. The PANTA processors are optimized to execute tasks like multi-layer composition, YUVRGB conversion, rotation, alpha-blending, gamma correction and others before presenting the frame buffer for display. This enables significant reduction of overall SoC dynamic power consumption through partial or complete offload of the GPU. Further reduction of power consumption in the PANTA DP-aided SoC is achieved thanks to preserving the minimum system memory bandwidth through reduction of the number

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