Android 上层界面到内核代码的完整的流程分析，以alarm为例子

Alarm 调用流程，alarm的流程实现了从上层应用一直到下面driver的调用流程，下面简单阐述：

涉及代码;
./packages/apps/DeskClock/src/com/android/deskclock/Alarms.java
./frameworks/base/core/java/android/app/AlarmManager.java
./frameworks/base/services/java/com/android/server/AlarmManagerService.java
./frameworks/base/services/jni/com_android_server_AlarmManagerService.cpp
./kernel/kernel/drivers/rtc/alarm-dev.c
./kernel/kernel/include/linux/android_alarm.h
./kernel/kernel/drivers/rtc/alarm.c
./kernel/kernel/drivers/rtc/interface.c
./kernel/kernel/drivers/rtc/rtc-pcf8563.c


./packages/apps/DeskClock/src/com/android/deskclock/AlarmReceiver.java


./kernel/arch/arm/configs/mmp2_android_defconfig
./kernel/kernel/kernel/.config  


点击Clock 应用程序，然后设置新闹钟，会调到  Alarms.java  里面的
public static long setAlarm(Context context, Alarm alarm) {
....
setNextAlert(context);
....
}
然后这里面也会调用到 
public static void setNextAlert(final Context context) {
        if (!enableSnoozeAlert(context)) {
            Alarm alarm = calculateNextAlert(context);   //new 一个新的alarm
            if (alarm != null) {
                enableAlert(context, alarm, alarm.time);
            } else {
                disableAlert(context);
            }
        }
    }
然后继续调用到
private static void enableAlert(Context context, final Alarm alarm, final long atTimeInMillis) {
.......
am.set(AlarmManager.RTC_WAKEUP, atTimeInMillis, sender);   //这里是RTC_WAKEUP, 这就保证了即使系统睡眠了，都能唤醒，闹钟工作（android平台关机闹钟好像不行）
.....
}

然后就调用到了AlarmManager.java 里面方法
    public void set(int type, long triggerAtTime, PendingIntent operation) {
        try {
            mService.set(type, triggerAtTime, operation);
        } catch (RemoteException ex) {
        }
    }

然后就调用到了AlarmManagerService.java  里面方法
public void set(int type, long triggerAtTime, PendingIntent operation) {
        setRepeating(type, triggerAtTime, 0, operation);
    }

然后继续调用
public void setRepeating(int type, long triggerAtTime, long interval,
            PendingIntent operation) {
.....
synchronized (mLock) {
            Alarm alarm = new Alarm();
            alarm.type = type;
            alarm.when = triggerAtTime;
            alarm.repeatInterval = interval;
            alarm.operation = operation;

            // Remove this alarm if already scheduled.
            removeLocked(operation);

            if (localLOGV) Slog.v(TAG, "set: " + alarm);

            int index = addAlarmLocked(alarm);
            if (index == 0) {
                setLocked(alarm);
            }
        }
    }

然后就调用到
private void setLocked(Alarm alarm)
    {
    ......
    set(mDescriptor, alarm.type, alarmSeconds, alarmNanoseconds);   //mDescriptor  这里的文件是 /dev/alarm
    .....
}

这里就调用到jni了
private native void set(int fd, int type, long seconds, long nanoseconds);

这就调用到了com_android_server_AlarmManagerService.cpp 里面
static JNINativeMethod sMethods[] = {
     /* name, signature, funcPtr */
    {"init", "()I", (void*)android_server_AlarmManagerService_init},
    {"close", "(I)V", (void*)android_server_AlarmManagerService_close},
    {"set", "(IIJJ)V", (void*)android_server_AlarmManagerService_set},
    {"waitForAlarm", "(I)I", (void*)android_server_AlarmManagerService_waitForAlarm},
    {"setKernelTimezone", "(II)I", (void*)android_server_AlarmManagerService_setKernelTimezone},
};

set 对应的是android_server_AlarmManagerService_set， 具体是
static void android_server_AlarmManagerService_set(JNIEnv* env, jobject obj, jint fd, jint type, jlong seconds, jlong nanoseconds)
{
#if HAVE_ANDROID_OS
    struct timespec ts;
    ts.tv_sec = seconds;
    ts.tv_nsec = nanoseconds;
   
    int result = ioctl(fd, ANDROID_ALARM_SET(type), &ts);
    if (result < 0)
    {
        LOGE("Unable to set alarm to %lld.%09lld: %s\n", seconds, nanoseconds, strerror(errno));
    }
#endif
}

然后ioctl 就调用到了alarm-dev.c
static long alarm_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
....
    case ANDROID_ALARM_SET(0):
        if (copy_from_user(&new_alarm_time, (void __user *)arg,
            sizeof(new_alarm_time))) {
            rv = -EFAULT;
            goto err1;
        }
from_old_alarm_set:
        spin_lock_irqsave(&alarm_slock, flags);
        pr_alarm(IO, "alarm %d set %ld.%09ld\n", alarm_type,
            new_alarm_time.tv_sec, new_alarm_time.tv_nsec);
        alarm_enabled |= alarm_type_mask;
        alarm_start_range(&alarms[alarm_type],
            timespec_to_ktime(new_alarm_time),
            timespec_to_ktime(new_alarm_time));
        spin_unlock_irqrestore(&alarm_slock, flags);
        if (ANDROID_ALARM_BASE_CMD(cmd) != ANDROID_ALARM_SET_AND_WAIT(0)
            && cmd != ANDROID_ALARM_SET_AND_WAIT_OLD)
            break;
        /* fall though */
....

case ANDROID_ALARM_SET_RTC:
        if (copy_from_user(&new_rtc_time, (void __user *)arg,
            sizeof(new_rtc_time))) {
            rv = -EFAULT;
            goto err1;
        }
        rv = alarm_set_rtc(new_rtc_time);
        spin_lock_irqsave(&alarm_slock, flags);
        alarm_pending |= ANDROID_ALARM_TIME_CHANGE_MASK;
        wake_up(&alarm_wait_queue);
        spin_unlock_irqrestore(&alarm_slock, flags);
        if (rv < 0)
            goto err1;
        break;
....
}

然后这边就调用到了alarm_start_range  设置闹钟，   alarm_set_rtc  设置RTC
这两个函数在 android_alarm.h 声明，在 alarm.c 里实现
这是android_alarm.h 里面的声明
void alarm_start_range(struct alarm *alarm, ktime_t start, ktime_t end);
int alarm_try_to_cancel(struct alarm *alarm);
int alarm_cancel(struct alarm *alarm);
ktime_t alarm_get_elapsed_realtime(void);

/* set rtc while preserving elapsed realtime */
int alarm_set_rtc(const struct timespec ts);

下面看alarm.c 里面实现：
int alarm_set_rtc(struct timespec new_time)
{
....
ret = rtc_set_time(alarm_rtc_dev, &rtc_new_rtc_time);
....
}

alarm.c  里面实现了 alarm_suspend  alarm_resume 函数
就是如果系统没有suspend的时候，设置闹钟并不会往rtc 芯片的寄存器上写数据，因为不需要唤醒系统，所以闹钟数据时间什么的就通过上层写到设备文件/dev/alarm
里面就可以了，AlarmThread 会不停的去轮寻下一个时间有没有闹钟，直接从设备文件 /dev/alarm 里面读取
第二种，系统要是进入susupend的话，alarm 的alarm_suspend  就会写到下层的rtc芯片的寄存器上去， 然后即使系统suspend之后，闹钟通过rtc 也能唤醒系统



这里就调用到了interface.c 里面   //这里面 int rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm) 差不多 也是跟下面一样
int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
{
....
    err = rtc->ops->set_time(rtc->dev.parent, tm);
....
}

然后set_time 就看到具体的是那个RTC芯片，这边我们是rtc-pcf8563.c
static const struct rtc_class_ops pcf8563_rtc_ops = {
    .read_time    = pcf8563_rtc_read_time,
    .set_time    = pcf8563_rtc_set_time,
    .read_alarm    = pcf8563_rtc_read_alarm,
    .set_alarm    = pcf8563_rtc_set_alarm,
};
然后就到了
static int pcf8563_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
    unsigned char buf[TIME_NUM];
    int ret;

    ret = data_calc(buf, tm, TIME_NUM);
    if (ret < 0)
        goto out;
    ret = i2c_smbus_write_i2c_block_data(pcf8563_info->client, PCF8563_RTC_SEC, TIME_NUM, buf);  //这边就调用i2c统一接口，往pcf8563rtc芯片寄存器里面写出数据
out:
    return ret;
}

到此，闹钟时间就已经写到rtc 芯片的寄存器里面，第二个参数就是寄存器的名字，后面的buf就是要写入的时间，rtc芯片是额外供电的，所以系统suspend之后，系统kernel都关了，但是rtc里面还有电，寄存器里面数据还是有的（掉电就会丢失数据），所以闹钟到了，通过硬件中断机制就可以唤醒系统。

上面那个rtc下面有几十个rtc芯片驱动代码，没有结构基本一样，都有基本操作函数，注册函数，都是对各自芯片上特有的寄存器操作，为什么调用的是pcf8563rtc呢？这个要看你系统用的是那个芯片，这个可以通过./kernel/kernel/kernel/.config  查看，这边的pcf8563rtc  是当前系统正在使用的芯片型号 
# CONFIG_RTC_DRV_ISL1208 is not set
# CONFIG_RTC_DRV_X1205 is not set
CONFIG_RTC_DRV_PCF8563=y
# CONFIG_RTC_DRV_PCF8583 is not set
# CONFIG_RTC_DRV_M41T80 is not set



下面是系统唤醒之后，闹钟怎么工作的流程，简单阐述
系统没有suspend的话直接走下面流程，如果suspend的话会被RTC唤醒，然后还是走下面的流程

private class AlarmThread extends Thread
    {
        public AlarmThread()
        {
            super("AlarmManager");
        }
       
        public void run()
        {
        while (true)
            {
        int result = waitForAlarm(mDescriptor); //这里调用jni调用static jint android_server_AlarmManagerService_waitForAlarm，主要还是对 /dev/alarm  操作
        ....
        Alarm alarm = it.next();
                        try {
                            if (localLOGV) Slog.v(TAG, "sending alarm " + alarm);
                            alarm.operation.send(mContext, 0,
                                    mBackgroundIntent.putExtra(
                                            Intent.EXTRA_ALARM_COUNT, alarm.count),
                                    mResultReceiver, mHandler);
        ....
        }

    }
      }


static jint android_server_AlarmManagerService_waitForAlarm(JNIEnv* env, jobject obj, jint fd)
{
#if HAVE_ANDROID_OS
    int result = 0;
   
    do
    {
        result = ioctl(fd, ANDROID_ALARM_WAIT);
    } while (result < 0 && errno == EINTR);
   
    if (result < 0)
    {
        LOGE("Unable to wait on alarm: %s\n", strerror(errno));
        return 0;
    }
   
    return result;
#endif
}

AlarmManagerService  里面有个AlarmThread  会一直轮询 /dev/alarm文件，如果打开失败就直接返回，成功就会做一些动作，比如查找时间最近的
alarm，比如睡眠被闹钟唤醒的时候，这边就发一个intent出去，然后在AlarmReceiver.java里面弹出里面会收到就会调用下面的
        context.startActivity(alarmAlert);

然后弹出alarm  这个界面
        Class c = AlarmAlert.class;
其中public class AlarmAlert extends AlarmAlertFullScreen  所以系统睡眠之后被alarm唤醒弹出的alarm就是这边start的
public class AlarmReceiver extends BroadcastReceiver {

    /** If the alarm is older than STALE_WINDOW, ignore.  It
        is probably the result of a time or timezone change */
    private final static int STALE_WINDOW = 30 * 60 * 1000;

    @Override
    public void onReceive(Context context, Intent intent) {
    .........
        Intent alarmAlert = new Intent(context, c);
        alarmAlert.putExtra(Alarms.ALARM_INTENT_EXTRA, alarm);
        alarmAlert.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                | Intent.FLAG_ACTIVITY_NO_USER_ACTION);
        context.startActivity(alarmAlert);
    ........
}

到这里alarm 就显示出来了

我个人添加的log，验证了流程，suspend和不suspend的时候alarm的区别跟上面说的一样