Category:How to - Low Power

Status

This page is a work in progress. Many users are running gumstix in power sensitive applications and therefore need to reduce power consumption as much as possible. There is no documentation available describing precisely the steps needed to reduce gumstix power consumption. As a result, I created this how to and am filling it in as I learn each step for reducing power.

Relevant Emails

sample numbers for Overo Earth power consumption

Building a linux omap3 pm for Overo

Background

The default omap3 openembedded build does not provide an optimal setup for power reduction on gumstix Overo COMS. In order to achieve the lowest power possible for your application, you have to perform a combination of the following:

• Use the latest OMAP Power Management (pm) kernel branch
• Enable power saving features such as sleep when idle and off mode
• Disable internal OMAP devices
• Hold unused external chips such as USB, Wifi, Bluetooth, etc. in reset
• Turn off unused LEDs

PM Kernel

The PM kernel is a development branch of the linux-omap kernel focused on developing the power management features of OMAP. Many of the changes of the PM branch have been merged to the mainstream linux-omap branch. Not all changes have been merged though so you must manually configure openembedded to use the PM kernel instead of the mainstream branch.

Compile PM Kernel

To enable the PM kernel edit the file

org.openembedded.dev/conf/machine/overo.conf

and change the line

PREFERRED_PROVIDER_virtual/kernel = "linux-omap3"

to

PREFERRED_PROVIDER_virtual/kernel = "linux-omap-pm"

Save the changes and then run bitbake as usual e.g.

$ bitbake omap3-console-image

The pm branch will be downloaded and compiled.

NOTE: Downloading the branch may take some time.

TODO: Add alternative method for downloading branch from mirror.

Once you have the PM kernel built, follow the instructions for copying the new image and filesystem to your microSD card.

Configure PM Kernel