Android系统如果没有电源管理相关的驱动程序，在启动时将会提示如下错误：

I/SystemServer(   50): Starting Battery Service.

E/BatteryService(   50): Could not open '/sys/class/power_supply/ac/online'

E/BatteryService(   50): Could not open '/sys/class/power_supply/usb/online'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/present'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/capacity'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/batt_vol'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/batt_temp'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/status'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/health'

E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/technology'

I/SystemServer(   50): Starting Hardware Service.

此时启动完成后将显示Poweroff界面

图1

图2

这个问题的原因很简单，因为缺少相关电源部分驱动程序，Android系统无法获取/sys/class/power_supply/下的信息，从而导致启动不能。

对于开发板，开发的初期一般没有电源管理驱动程序，那要如何解决这个问题呢？

网上流传的解决办法是通过修改Android源码中的com_android_server_BatteryService.cpp，让android系统不去去读相关信息，强行赋值为电量充足。

但是如果无法重新编译android文件系统，应该如何处理？

其实，有一个更好的解决方法，就是在Linux内核中写一个虚拟电源驱动，这样的好处是增加电源芯片后，直接在此驱动上修改即可，也不用修改Android源码了。

/sys/class # cd power_supply/

/sys/class/power_supply # ls

ac       battery

/sys/class/power_supply # cd battery/

/sys/class/power_supply/battery # ls

capacity        manufacturer    subsystem       uevent

charge_counter power           technology      voltage_avg

current_avg     present         temp

device          serial_number   temp_ambient

health          status          type

/sys/class/power_supply/battery #

驱动源码：

=========================================================================================================

/*

* Fake Battery driver for android

*

* Copyright © 2009 Rockie Cheng < aokikyon@gmail.com >

*

* This program is free software; you can redistribute it and/or modify

* it under the terms of the GNU General Public License version 2 as

* published by the Free Software Foundation.

*/

#include

#include

#include

#include

#include

#include

#define BAT_STAT_PRESENT 0x01

#define BAT_STAT_FULL   0x02

#define BAT_STAT_LOW   0x04

#define BAT_STAT_DESTROY 0x08

#define BAT_STAT_AC   0x10

#define BAT_STAT_CHARGING 0x20

#define BAT_STAT_DISCHARGING 0x40

#define BAT_ERR_INFOFAIL 0x02

#define BAT_ERR_OVERVOLTAGE 0x04

#define BAT_ERR_OVERTEMP 0x05

#define BAT_ERR_GAUGESTOP 0x06

#define BAT_ERR_OUT_OF_CONTROL 0x07

#define BAT_ERR_ID_FAIL   0x09

#define BAT_ERR_ACR_FAIL 0x10

#define BAT_ADDR_MFR_TYPE 0x5F

static int android_ac_get_prop(struct power_supply *psy,

enum power_supply_property psp,

union power_supply_propval *val)

{

switch (psp)

{

case POWER_SUPPLY_PROP_ONLINE:

val->intval = BAT_STAT_AC;

break;

default:

break;

}

return 0;

}

static enum power_supply_property android_ac_props[] =

{

POWER_SUPPLY_PROP_ONLINE,

};

static struct power_supply android_ac =

{

.name = "ac",

.type = POWER_SUPPLY_TYPE_MAINS,

.properties = android_ac_props,

.num_properties = ARRAY_SIZE(android_ac_props),

.get_property = android_ac_get_prop,

};

static int android_bat_get_status(union power_supply_propval *val)

{

val->intval = POWER_SUPPLY_STATUS_FULL;

return 0;

}

static int android_bat_get_health(union power_supply_propval *val)

{

val->intval = POWER_SUPPLY_HEALTH_GOOD;

return 0;

}

static int android_bat_get_mfr(union power_supply_propval *val)

{

val->strval = "Rockie";

return 0;

}

static int android_bat_get_tech(union power_supply_propval *val)

{

val->intval = POWER_SUPPLY_TECHNOLOGY_LION;

return 0;

}

static int android_bat_get_property(struct power_supply *psy,

enum power_supply_property psp,

union power_supply_propval *val)

{

int ret = 0;

switch (psp)

{

case POWER_SUPPLY_PROP_STATUS:

ret = android_bat_get_status(val);

if (ret)

return ret;

break;

case POWER_SUPPLY_PROP_PRESENT:

val->intval = BAT_STAT_PRESENT;

break;

case POWER_SUPPLY_PROP_HEALTH:

ret = android_bat_get_health(val);

break;

case POWER_SUPPLY_PROP_MANUFACTURER:

ret = android_bat_get_mfr(val);

if (ret)

return ret;

break;

case POWER_SUPPLY_PROP_TECHNOLOGY:

ret = android_bat_get_tech(val);

if (ret)

return ret;

break;

case POWER_SUPPLY_PROP_VOLTAGE_AVG:

val->intval = 3;

break;

case POWER_SUPPLY_PROP_CURRENT_AVG:

val->intval = 3;

break;

case POWER_SUPPLY_PROP_CAPACITY:

val->intval = 100;

break;

case POWER_SUPPLY_PROP_TEMP:

val->intval = 50;

break;

case POWER_SUPPLY_PROP_TEMP_AMBIENT:

val->intval = 50;

break;

case POWER_SUPPLY_PROP_CHARGE_COUNTER:

val->intval = 10;

break;

case POWER_SUPPLY_PROP_SERIAL_NUMBER:

break;

default:

ret = -EINVAL;

break;

}

return ret;

}

static enum power_supply_property android_bat_props[] = {

POWER_SUPPLY_PROP_STATUS,

POWER_SUPPLY_PROP_PRESENT,

POWER_SUPPLY_PROP_HEALTH,

POWER_SUPPLY_PROP_TECHNOLOGY,

POWER_SUPPLY_PROP_VOLTAGE_AVG,

POWER_SUPPLY_PROP_CURRENT_AVG,

POWER_SUPPLY_PROP_CAPACITY,

POWER_SUPPLY_PROP_TEMP,

POWER_SUPPLY_PROP_TEMP_AMBIENT,

POWER_SUPPLY_PROP_MANUFACTURER,

POWER_SUPPLY_PROP_SERIAL_NUMBER,

POWER_SUPPLY_PROP_CHARGE_COUNTER,

};

/*********************************************************************

*   Initialisation

*********************************************************************/

static struct platform_device *bat_pdev;

static struct power_supply android_bat =

{

.properties = android_bat_props,

.num_properties = ARRAY_SIZE(android_bat_props),

.get_property = android_bat_get_property,

.use_for_apm = 1,

};

static int __init android_bat_init(void)

{

int ret = 0;

bat_pdev = platform_device_register_simple("battery", 0, NULL, 0);

ret = power_supply_register(&bat_pdev->dev, &android_ac);

if (ret)

goto ac_failed;

android_bat.name = bat_pdev->name;

ret = power_supply_register(&bat_pdev->dev, &android_bat);

if (ret)

goto battery_failed;

goto success;

power_supply_unregister(&android_bat);

battery_failed:

power_supply_unregister(&android_ac);

ac_failed:

platform_device_unregister(bat_pdev);

success:

return ret;

}

static void __exit android_bat_exit(void)

{

power_supply_unregister(&android_bat);

power_supply_unregister(&android_ac);

platform_device_unregister(bat_pdev);

}

module_init(android_bat_init);

module_exit(android_bat_exit);

MODULE_AUTHOR("Rockie Cheng < aokikyon@gmail.com >");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("Fake Battery driver for android");

==================================================================================================================

阿虚(Rockie Cheng)

如有错误，欢迎指正！