Power Consumption Modes (Windows CE 5.0)
While running, Windows CE target devices can generally be in one of three power consumption modes:
- Off. All power supplies are disconnected. The target device does not consume any power. The device enters this mode when a user presses the power button to turn off the device.
- Idle. The CPU has power but is not executing instructions or generating a clock signal. The device enters this mode when there are no threads ready to run.
- Active. The CPU has power and is executing instructions. RAM, flash memory, and other peripherals are active and are consuming power. The target device enters this mode when the user presses the power button to turn on the device or when a thread is ready to run.
The amount of power that a device consumes is the sum of the power consumed while idle and the power consumed while active.
Target devices typically spend the vast majority of their time in idle mode. For example, Windows Mobile Pocket PCs are often idle except for the instant that a stylus touches the screen, a key is pressed, or a peripheral generates an interrupt.
Because a device is usually in idle mode, often the most effective way to reduce power consumption is to reduce the amount of power consumed while idle.
Idle power consumption is typically dominated by the following hardware components:
- CPU
- SDRAM
- Display
- Display frontlight/backlight
The relative amount of power each of these hardware components consumes depends on the nature of the device and how the device is used. In most cases, the display frontlight/backlight consumes the most power. The display consumes more power than anything but the frontlight/backlight. When the CPU is idle, SDRAM usually consumes more power than the CPU; this relationship is switched when the CPU is active: the CPU then usually consumes more power than SDRAM.
For more information, see Hardware Considerations for Battery Life.
Idle power consumption is also affected by software considerations, such as:
- Device driver management of peripheral devices.
- Target device or peripheral device polling behavior.
For more information, see Software Considerations for Battery Life.
See Also
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