Power Policy Manager

How the Power Policy Manager (PPM) works

With a layered approach, many power modes can be active at once, without hard-coding exceptions. Among the active power modes, system-determined hierarchies prevent power mode conflicts.

The Framework The PPM breaks down power policy management by using plug-ins, layers, and modes.

• Modes determines which layers to use.
• Layers contains the list of commands.
• Plug-ins communicate the commands to the hardware.

A mode contains the list of which layers to activate. Multiple modes can be active at the same time. If two modes select different layers, the commands sent to the plug-ins will be based on a combination of the layers. Higher priority layers take precedence.

For example, if one layer had the plug-in command, "cpu performance max", but a higher priority layer had the plug-in command, "cpu performance cool", the latter command would be sent to the cpu plug-in. Layers are transparent, which means that commands from lower priority layers that don’t overlap with commands from higher priority layers, are active.

A policy layer is a grouping of plug-in commands, with an associated priority.

Example layer 1 For example, a low-power layer might contain commands to:

• set the CPU to a low-power mode
• set the screensaver timeout to 2 minutes
• dim the screen

Example layer 2 A second layer, dealing with thermal issues, might:

• set the screensaver timeout to 30 seconds
• put the SATA hard drive into low power mode
• tell the CPU to go into "cool" mode

Which layer takes precedence? The thermal policy layer would have the highest priority, to make sure that the system doesn’t overheat.

Code example A layer file would look something like this (first release is simple text description):

• File name convention: Priority_Name (for example: 00_default)
• Policy file structure is three columns and N number of rows.
• First column is CLASS, referring to device classes.
• Second column is COMMAND, referring to operation to be invoked on the device or subsystem.
• Third column is VALUE, such as ON, OFF, MAX (depending on the device).

Layer content An example of the 00_default policy:

CPU		Performance	Max
radio		radio		allowed
wifi		radio		on
display		screensaver	user
display		brightness	50
bt		radio		off