System Power States (Compact 2013)
3/26/2014
Power Manager manages device power states within the context of system power states that you define, and you define these system power states as registry keys in your system configuration. You are also responsible for creating explicit mappings between your platform’s system power states and the predefined device power states of Windows Embedded Compact 2013. You define these mappings as registry values associated with system power state registry keys. For more information about how to define these power state mappings, see Implement System Power States.
Any given system power state explicitly specifies the maximum device power state for all devices in the system. You can define the system power states for your platform, and you can refer to these states by names that you choose (such as On, SystemIdle, OnBattery, InCradle, OutOfCradle, and so on). In Windows Embedded Compact 2013, there is no limit to how many system power states you can define, and the names of the power states do not have to be arranged from high-powered/high-function to low-power/low-function (as is necessary with power management mechanisms such as the Advanced Configuration and Power Interface (ACPI) model). In general, a system power state defines the maximum device power state for all devices in the system; it effectively defines the "ceiling" for device power state.
The following table describes some examples of system power states as implemented by the Power Manager sample code described later in this article.
System Power States
System Power State |
Description |
|---|---|
On |
Normal operating state when a user is interacting with the device. |
Resuming |
Initial state after the device wakes up from the Suspended state. |
BacklightOff |
State after a short period of user inactivity. The backlight is off, but other hardware components could also be turned off. |
ScreenOff |
State for applications that must turn off the screen through the display driver. A typical case is Windows Media Player, which can turn off the screen through a user-defined key press. |
Suspended |
Sleep state. No threads are running and the CPU is idle. The system can wake up only by means of a hardware wake-source interrupt. |
SystemIdle |
The user is not using the system, even passively. However, the system is not suspended and system programs may be running. Devices that are not actively doing work may be turned off. |
Unattended |
State in which a program runs without the user's knowledge or the need for interaction from the user (such as a synchronization program). Upon exiting such a program, the device goes directly to the Suspended state without waiting for the system idle timer to expire. |
UserIdle |
State after a longer period of user inactivity. The screen is either in low-power mode or powered off, depending on your configuration. Other hardware components could also be turned off. |
The UserIdle state is intended for situations when the user is using the device but is not actively interacting with it; for example, when the user is looking at the display. The SystemIdle state is intended for situations when the user is not directly using the system and might consider the device to be idle. For example, the user may stop using the system while system processes (such as file transfer operations) are still active.