Alarm 硬件时钟

Alarm就是一个硬件时钟，用于把设备从睡眠状态唤醒，同时它也提供了一个在设备睡眠时仍然会运行的时钟基准。基于内核的rtc机制完成。

Alarm的设备名为“/dev/alarm”。

“./include/linux/android_alarm.h”

 /drivers/rtc/alarm.c

enum android_alarm_type { /* return code bit numbers or set alarm arg */ ANDROID_ALARM_RTC_WAKEUP, // 表示触发Alarm时需要唤醒设备，反之则不需要唤醒设备 ANDROID_ALARM_RTC, // 表示在指定的某一时刻发出alarm ANDROID_ALARM_ELAPSED_REALTIME_WAKEUP, // ?? ANDROID_ALARM_ELAPSED_REALTIME, // 表示在设备启动后，流逝的时间达到总时间之后触发alarm ANDROID_ALARM_SYSTEMTIME, // 表示系统时间 ANDROID_ALARM_TYPE_COUNT, // alarm类型的计数 /* return code bit numbers */ /* ANDROID_ALARM_TIME_CHANGE = 16 */ };

/** * struct alarm - the basic alarm structure * @node: red black tree node for time ordered insertion * @type: alarm type. rtc/elapsed-realtime/systemtime, wakeup/non-wakeup. * @softexpires: the absolute earliest expiry time of the alarm. * @expires: the absolute expiry time. * @function: alarm expiry callback function * * The alarm structure must be initialized by alarm_init() * */ struct alarm { struct rb_node node; enum android_alarm_type type; ktime_t softexpires; ktime_t expires; void (*function)(struct alarm *); };