[转] Android电源管理

First written by Steve Guo, please keep the mark if forwarding.

Overview



The above picture shows the overall architecture design of Android
power management module. Android implements a very simple power
management mechanism. Currently it only supports set screen on/off,
screen backlight on/off, keyboard backlight on/off, button backlight
on/off and adjust screen brightness. It does not support Sleep or
Standby mode to fully use CPU’s capability.

The power management module has three channels to receive input: RPC
call, Batter state change event and Power Setting change event. It
communicated with other modules through either broadcasting intent or
directly API call. The module also provide reboot and shutdown service.
When battery is lower than thredshold, it will automatically shutdown
the device.

The module will automatically set screen dim and off according to
whether any user activity happens or not. The full state machine is
shown as follows:



Detail

PowerManagerService.java is the core service. It calls Power.java to do the real work.

PowerManager.java is the proxy to RPC call PowerManagerService.java.

Power.java communicates with the low level through JNI.

android_os_Power.cpp is the JNI native implementation for Power.java. It calls Power.c to do the real work.

Power.c controls the power device driver through read/write the following sys files.

"/sys/android_power/acquire_partial_wake_lock",

"/sys/android_power/acquire_full_wake_lock",

"/sys/android_power/release_wake_lock",

"/sys/android_power/request_state"

"/sys/android_power/auto_off_timeout",

"/sys/class/leds/lcd-backlight/brightness",

"/sys/class/leds/button-backlight/brightness",

"/sys/class/leds/keyboard-backlight/brightness"

BatteryService.java registers itself as a UEvent observer for the
path “/sys/class/power_supply”. If anything is changed in this path, it
gets current state through JNI and then broadcasts
ACTION_BATTERY_CHANGED intent.

com_android_server_BatteryService.cpp is the JNI native
implementation for BatteryService.java. It gets current battery state
through reading from the following files:

"/sys/class/power_supply/ac/online"

"/sys/class/power_supply/usb/online"

"/sys/class/power_supply/battery/status"

"/sys/class/power_supply/battery/health"

"/sys/class/power_supply/battery/present"

"/sys/class/power_supply/battery/capacity"

"/sys/class/power_supply/battery/batt_vol"

"/sys/class/power_supply/battery/batt_temp"

"/sys/class/power_supply/battery/technology"

How to use

To call power module in app, the following is the sample code:

PowerManager pm = (PowerManager)mContext.getSystemService(Context.POWER_SERVICE);

PowerManager.WakeLock wl = pm.newWakeLock(

PowerManager.SCREEN_DIM_WAKE_LOCK

| PowerManager.ON_AFTER_RELEASE,

TAG);

wl.acquire();

// ...

wl.release();