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
*
* 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
");MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Fake Battery driver for android");
==================================================================================================================
阿虚（Rockie Cheng）
本文为原创，转载请注明出处
如有错误，欢迎指正！
