基于Andriod系统的平台在没有硬件充电指示的情况下只有进入andriod系统才能进行充电指示，而我们有时候仅仅需要充电而不需要进入系统，本文介绍了实现这种功能的方法。
具体过程如下：当内核启动后调用充电指示控制程序。充电指示程序发现如果外部供电就开始显示充电的画面，同时将设备的电源控制锁定为关闭状态（这样当拔掉电源时候系统自动关闭），如果在充电指示过程中又按了开机键，就重新开启电源按键。这个过程在单片机等简单系统上不值得一提，因为每个人都会想的比我好，这里重点介绍如何融合到andriod系统以及其中的我认为可以让别人参考的方法。
方法一 ui显示部分。显然我们不能让系统跑的太深，否则控制起来就过于麻烦，充电显示等老半天才启动别人也觉得奇怪。所以有必要仅仅使用微型系统，微型系统自然能用的功能就少，在图像显示上面只能使用c语言操作framebuff，我的方法是参考bootable/recovery/minui/里面的库，其支持png的图片也文本显示，对于充电指示足够用了。一个可能遇到的问题是andriod提供的minui显示使用驱动的双buffer机制，在有的系统上不具备该功能，你可以强制只使用一个，修改graphics.c的函数gr_flip，将gr_active_fb 赋值为0。
方法二 电池检测。 可以参考com_andriod_server_batteryService.cpp文件，基本上把里面的函数复制过来就可以使用。
完成的charge充电程序必须加入到init.rc中才能被调用，我把它当做一个只运行一次的服务运行。
service console /system/bin/busybox sh
console
#shuaiwen added,init.c has been hacked to block to wait this process to finish
service charge /system/bin/charge
oneshot
在init启动服务的过程都是非阻塞型的（新开一个线程运行），这会导致虽然服务已经被加入，但是系统还会完整启动，显然不能满足要求，实际的需求为当charge运行起来不应该运行其他服务。要实现这个目的，必须对init.c进行一点修改。我的方法是让init对启动的服务名称做判断，如果为charge就等待到该程序结束才继续运行。具体修改为改动init.c的函数service_start：
if (pid == 0) {
……..
}
//shuaiwen added begin
else{
int status;
if(strcmp(svc->name,"charge")==0)
{
wait(&status); //wait child to exist
load_565rle_image(INIT_IMAGE_FILE);//redraw background
}
// else printf("shuaiwen skip process %s.",svc->name);
}
//shuaiwen added end
if (pid < 0) {
….}
这样系统就会被charge阻塞住。Init.rc中排在charge后面的服务就暂时不会被启动。我上面改动的init.rc把charge服务放在console服务后面是因为我还是需要控制台调试。经过这样的改动，基本的充电服务就可以实现。我这里仅仅是举了一个例子，文中的例子仅仅供参考，请酌情参考。
我写的一个简单的充电指示文件内容列在下面供大家参考。
/*
Copyright:GNU
charge monitor.
revision history:
2010/5/10 create shuaiwen
icon path:
/res/images/%s.png
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/input.h>
#include <pthread.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/reboot.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include "minui/minui.h"
#include "minzip/Zip.h"
#define KEY_PWR 116
#define AC_ONLINE_PATH "/sys/class/power_supply/ac/online"
#define USB_ONLINE_PATH "/sys/class/power_supply/usb/online"
#define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status"
#define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health"
#define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present"
#define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity"
#define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol"
#define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp"
#define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology"
enum {
BACKGROUND_ICON_CHARGE0,
BACKGROUND_ICON_CHARGE1,
BACKGROUND_ICON_CHARGE2,
BACKGROUND_ICON_CHARGE3,
BACKGROUND_ICON_CHARGE4,
BACKGROUND_ICON_CHARGE5,
BACKGROUND_ICON_END,
};
enum {
STATUSCHARGING,
STATUSDISCHARGING,
STATUSFULL,
STATUSNOTCHARGING,
STATUSUNKNOWN
};
enum{
HEALTHDEAD,
HEALTHGOOD,
HEALTHOVERHEAT,
HEALTHOVERVOLTAGE,
HEALTHUNKNOWN,
HEALTHUNSPECIFIEDFAILURE,
};
static gr_surface gBackgroundIcon[BACKGROUND_ICON_END];
static const struct { gr_surface* surface; const char *name; } BITMAPS[] = {
{ &gBackgroundIcon[BACKGROUND_ICON_CHARGE0], "battery001" },
{ &gBackgroundIcon[BACKGROUND_ICON_CHARGE1], "battery002" },
{ &gBackgroundIcon[BACKGROUND_ICON_CHARGE2], "battery003" },
{ &gBackgroundIcon[BACKGROUND_ICON_CHARGE3], "battery004" },
{ &gBackgroundIcon[BACKGROUND_ICON_CHARGE4], "battery005" },
{ &gBackgroundIcon[BACKGROUND_ICON_CHARGE5], "battery006" },
{ NULL, NULL },
};
static int readFromFile(const char* path, char* buf, size_t size)
{
int fd = open(path, O_RDONLY, 0);
if (fd == -1) {
//LOGE("Could not open '%s'", path);
return -1;
}
size_t count = read(fd, buf, size);
if (count > 0) {
count = (count < size) ? count : size - 1;
while (count > 0 && buf[count-1] == '\n') count--;
buf[count] = '\0';
} else {
buf[0] = '\0';
}
close(fd);
return count;
}
static int getBatteryStatus(const char* status)
{
switch (status[0]) {
case 'C': return STATUSCHARGING; // Charging
case 'D': return STATUSDISCHARGING; // Discharging
case 'F': return STATUSFULL; // Not charging
case 'N': return STATUSNOTCHARGING; // Full
case 'U': return STATUSUNKNOWN; // Unknown
default: {
printf("Unknown battery status '%s'", status);
return STATUSUNKNOWN;
}
}
}
static int getBatteryHealth(const char* status)
{
switch (status[0]) {
case 'D': return HEALTHDEAD; // Dead
case 'G': return HEALTHGOOD; // Good
case 'O': {
if (strcmp(status, "Overheat") == 0) {
return HEALTHOVERHEAT;
} else if (strcmp(status, "Over voltage") == 0) {
return HEALTHOVERVOLTAGE;
}
printf("Unknown battery health[1] '%s'", status);
return HEALTHUNKNOWN;
}
case 'U': {
if (strcmp(status, "Unspecified failure") == 0) {
return HEALTHUNSPECIFIEDFAILURE;
} else if (strcmp(status, "Unknown") == 0) {
return HEALTHUNKNOWN;
}
// fall through
}
default: {
printf("Unknown battery health[2] '%s'", status);
return HEALTHUNKNOWN;
}
}
}
static void ui_set_background(int icon)
{
gr_surface gIcon;
gIcon=gBackgroundIcon[icon];
gr_color(0, 0, 0, 255);
gr_fill(0, 0, gr_fb_width(), gr_fb_height());
if (gIcon) {
//printf("set backgroupd:%s\n\r",gBackgroundIcon[icon].name);
int iconWidth = gr_get_width(gIcon);
int iconHeight = gr_get_height(gIcon);
int iconX = (gr_fb_width() - iconWidth) / 2;
int iconY = (gr_fb_height() - iconHeight) / 2;
gr_blit(gIcon, 0, 0, iconWidth, iconHeight, iconX, iconY);
}
gr_flip();
}
static void ui_init()
{
gr_init();
ev_init();
int i;
for (i = 0; BITMAPS[i].name != NULL; ++i) {
int result = res_create_surface(BITMAPS[i].name, BITMAPS[i].surface);
if (result < 0) {
printf("Missing bitmap %s\n(Code %d)\n", BITMAPS[i].name, result);
*BITMAPS[i].surface = NULL;
}
//else printf("create:%s\n\r",BITMAPS[i].name);
}
}
const int SIZE = 128;
int power_ac()
{
char buf[SIZE];
if (readFromFile(AC_ONLINE_PATH, buf, SIZE) > 0) {
if (buf[0] == '1') {
return 1;
}
}
return 0;
}
/*
function to indicate if the battery is present.
*/
int battery_present()
{
char buf[SIZE];
if (readFromFile(BATTERY_PRESENT_PATH, buf, SIZE) > 0) {
if (buf[0] == '1') {
return 1;
}
}
return 0;
}
int battery_capacity()
{
char buf[SIZE];
if (readFromFile(BATTERY_CAPACITY_PATH, buf, SIZE) > 0) {
return atoi(buf);
}
return 0;
}
int battery_voltage()
{
char buf[SIZE];
if (readFromFile(BATTERY_VOLTAGE_PATH, buf, SIZE) > 0) {
return atoi(buf);
}
return 0;
}
int battery_temperature()
{
char buf[SIZE];
if (readFromFile(BATTERY_TEMPERATURE_PATH, buf, SIZE) > 0) {
return atoi(buf);
}
return 0;
}
int capacity_full()
{
char buf[SIZE];
if (readFromFile(BATTERY_STATUS_PATH, buf, SIZE) > 0)
{
return getBatteryStatus(buf);
}
}
void do_nothing() //don't commnet it before fix zip error. shuaiwen
{
ZipArchive zip;
mzOpenZipArchive(NULL, &zip);
}
int main(int argc, char **argv)
{
int index=0;
#define CIRCLE 100 //1000x1000 microsecond
int circle=0;//interval to update battery status.
struct input_event ev;
//is AC power charging?
if(!power_ac())
{
printf("battery supply,don't enter charge mode.\n\r");
return 0; //continue runing.
}
printf("entern charge mode\n\r");
//powerio_low(); //fixme,set power io low to shutdown system when unplug the power.
ui_init();
while(1)
{
circle=0;
ui_set_background(capacity_full()==STATUSCHARGING?index++%BACKGROUND_ICON_END:BACKGROUND_ICON_END-1);//todo:more condition must be considered.
// ui_set_background(index++%BACKGROUND_ICON_END);
while(circle++<CIRCLE)
{
usleep(1000);
ev_get(&ev, 10);
if((ev.type == EV_KEY)&&(ev.code==62))
{
// powerio_high(); //fixme
ev_exit();
gr_exit();
return 0;//the system will continue running
}
//debug
if(ev.type==EV_KEY)printf("key:%d pressed\n",ev.code);
//
}
}
ev_exit();
gr_exit();
return 0;
}
对应的andriod.mk文件如下：
LOCAL_PATH :=$(call my-dir)
include $(CLEAR_VARS)
charge_local_path := $(LOCAL_PATH)
LOCAL_SRC_FILES :=main.c
LOCAL_MODULE := charge
LOCAL_FORCE_STATIC_EXECUTABLE := true
# This binary is in the recovery ramdisk, which is otherwise a copy of root.
# It gets copied there in config/Makefile. LOCAL_MODULE_TAGS suppresses
# a (redundant) copy of the binary in /system/bin for user builds.
# TODO: Build the ramdisk image in a more principled way.
LOCAL_MODULE_TAGS := eng
LOCAL_STATIC_LIBRARIES := libminzip libunz libminui libpixelflinger_static libpng libcutils libstdc++ libc
include $(BUILD_EXECUTABLE)
include $(charge_local_path)/minui/Android.mk
include $(charge_local_path)/minzip/Android.mk
PRODUCT_COPY_FILES += \
$(charge_local_path)/res/images/battery001.PNG:system/res/images/battery001.png \
$(charge_local_path)/res/images/battery002.PNG:system/res/images/battery002.png \
$(charge_local_path)/res/images/battery003.PNG:system/res/images/battery003.png \
$(charge_local_path)/res/images/battery004.PNG:system/res/images/battery004.png \
$(charge_local_path)/res/images/battery005.PNG:system/res/images/battery005.png \