Android电源管理-休眠简要分析

工作需要，需要对这一块深入学习。故在此做一点分析记录，存疑解惑。

一、开篇

1.Linux 描述的电源状态

- On（on） S0 - Working

- Standby （standby） S1 - CPU and RAM are powered but not executed

- Suspend to RAM（mem) S3 - RAM is powered and the running content is saved to RAM

- Suspend to Disk，Hibernation（disk） S4 - All content is saved to Disk and power down

S3 aka STR(suspend to ram),挂起到内存，简称待机。计算机将目前的运行状态等数据存放在内存，关闭硬 盘、外设等设备，进入等待状态。此时内存仍然需要电力维持其数据，但整机耗电很少。恢复时计算机从内存读出数据，回到挂起前的状态，恢复速度较快。对 DDR的耗电情况进行优化是S3性能的关键，大多数手持设备都是用S3待机。

S4 aka STD(suspend to disk),挂起到硬盘，简称休眠。把运行状态等数据存放在硬盘上某个文件或者某个特定的区域，关闭硬盘、外设等设备，进入关机状态。此时计算机完全关闭，不耗电。恢复时计算机从休眠文件/分区中读出数据，回到休眠前的状态，恢复速度较慢。电子书项目中，见过一款索尼的电子书，没有定义关机状态，只定义了S4,从而提高开机速度。

以上摘录自：http://cache.baiducontent.com/c?m=9f65cb4a8c8507ed4fece763104

6893b4c4380147d8c8c4668d4e419ce3b4c413037bfa6663f405a8e906b6075fc

4d5bedfb6079370123b598938f4a85ac925f75ce786a6459db0144dc5bf0dc475

5d627e44de8df4aa0fcad7384afa28d880311dd52756d87849c5b704f9634b6&p

=c933cc16d9c116f51ebd9b7d0a13cd&newp=8366c54ad5c444e411b3c22d0214cf2

31610db2151d6db10349dcd1e&user=baidu&fm=sc&query=pm_autosleep_init&qid=&p1=1

在阅读下面的内容之前，强烈建议阅读下。

Android在Linux内核原有的睡眠唤醒机制上面新增了三个，如下：

• Wake Lock 唤醒锁机制；

• Early Suspend 预挂起机制；

• Late Resume 迟唤醒机制；

我们来看一张Android睡眠唤醒机制的框架图：

void request_suspend_state(suspend_state_t new_state)
{
unsigned long irqflags;
int old_sleep;

#ifdef CONFIG_PLAT_RK
if (system_state != SYSTEM_RUNNING)
return;
#endif

spin_lock_irqsave(&state_lock, irqflags);
old_sleep = state & SUSPEND_REQUESTED;
if (debug_mask & DEBUG_USER_STATE) {
struct timespec ts;
struct rtc_time tm;
getnstimeofday(&ts);
rtc_time_to_tm(ts.tv_sec, &tm);
pr_info("request_suspend_state: %s (%d->%d) at %lld "
"(%d-%02d-%02d %02d:%02d:%02d.%09lu UTC)\n",
new_state != PM_SUSPEND_ON ? "sleep" : "wakeup",
requested_suspend_state, new_state,
ktime_to_ns(ktime_get()),
tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec, ts.tv_nsec);
}
if (!old_sleep && new_state != PM_SUSPEND_ON) {
state |= SUSPEND_REQUESTED;
//进入Early suspend处理，执行函数early_suspend
queue_work(suspend_work_queue, &early_suspend_work);
} else if (old_sleep && new_state == PM_SUSPEND_ON) {
state &= ~SUSPEND_REQUESTED;
wake_lock(&main_wake_lock);
//进入Late resume处理,执行函数late_resume
queue_work(suspend_work_queue, &late_resume_work);
}
requested_suspend_state = new_state;
spin_unlock_irqrestore(&state_lock, irqflags);
}

View Code

TAG：

const char * const OLD_PATHS[] = {
"/sys/android_power/acquire_partial_wake_lock",
"/sys/android_power/release_wake_lock",
};

const char * const NEW_PATHS[] = {
"/sys/power/wake_lock",
"/sys/power/wake_unlock",
};

static inline void
initialize_fds(void)
{
// XXX: should be this:
//pthread_once(&g_initialized, open_file_descriptors);
// XXX: not this:
if (g_initialized == 0) {
if(open_file_descriptors(NEW_PATHS) < 0)
open_file_descriptors(OLD_PATHS);
g_initialized = 1;
}

未完待续......

本文很多内容参考且摘录自：
http://blog.csdn.net/myarrow/article/details/8136691 http://blog.csdn.net/myarrow/article/details/8137952 http://blog.csdn.net/myarrow/article/details/8137566 http://blog.csdn.net/sunweizhong1024/article/details/17102047