前言

當Linux內核啟動時，它會從RTC中讀取時間與日期，作為基準值。然后通過軟件來維護系統時間和日期。Linux系統中提供了RTC核心層，對于驅動開發者而言，操作起來就變得很簡單了。我們來看看整體框架。

驅動框架

下面是整體框架圖 ：

與RTC核心有關的文件有：

重要結構體

• rtc_device

//RTC設備
struct rtc_device {
  struct device dev;
  struct module *owner;


  int id;


  const struct rtc_class_ops *ops; //rtc操作函數
  struct mutex ops_lock;


  struct cdev char_dev;
  unsigned long flags;


  unsigned long irq_data;
  spinlock_t irq_lock;
  wait_queue_head_t irq_queue;
  struct fasync_struct *async_queue;


  int irq_freq;
  int max_user_freq;


  struct timerqueue_head timerqueue;
  struct rtc_timer aie_timer; 
  struct rtc_timer uie_rtctimer;
  struct hrtimer pie_timer; /* sub second exp, so needs hrtimer */
  int pie_enabled;
  struct work_struct irqwork;
  /* Some hardware can't support UIE mode */
  int uie_unsupported;


  long set_offset_nsec;


  bool registered;


  struct nvmem_device *nvmem;
  /* Old ABI support */
  bool nvram_old_abi;
  struct bin_attribute *nvram;


  time64_t range_min;
  timeu64_t range_max;
  time64_t start_secs;
  time64_t offset_secs;
  bool set_start_time;


#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
  struct work_struct uie_task;
  struct timer_list uie_timer;
  /* Those fields are protected by rtc->irq_lock */
  unsigned int oldsecs;
  unsigned int uie_irq_active:1;
  unsigned int stop_uie_polling:1;
  unsigned int uie_task_active:1;
  unsigned int uie_timer_active:1;
#endif
};

上面的結構體表示一個RTC設備，比較簡單，主要就是中斷信息，字符設備對象，操作函數等。

• rtc_class_ops

//RTC操作函數
struct rtc_class_ops {
  int (*ioctl)(struct device *, unsigned int, unsigned long);
  int (*read_time)(struct device *, struct rtc_time *);
  int (*set_time)(struct device *, struct rtc_time *);
  int (*read_alarm)(struct device *, struct rtc_wkalrm *);
  int (*set_alarm)(struct device *, struct rtc_wkalrm *);
  int (*proc)(struct device *, struct seq_file *);
  int (*set_mmss64)(struct device *, time64_t secs);
  int (*set_mmss)(struct device *, unsigned long secs);
  int (*read_callback)(struct device *, int data);
  int (*alarm_irq_enable)(struct device *, unsigned int enabled);
  int (*read_offset)(struct device *, long *offset);
  int (*set_offset)(struct device *, long offset);
};

就是一些設置時間和讀取時間，以及鬧鐘等接口函數。

• rtc_time

//時間結構體
struct rtc_time {
  int tm_sec;
  int tm_min;
  int tm_hour;
  int tm_mday;
  int tm_mon;
  int tm_year;
  int tm_wday;
  int tm_yday;
  int tm_isdst;
};

API函數

// 注冊RTC class
static struct rtc_device *rtc_device_register(const char *name,
                struct device *dev,
                const struct rtc_class_ops *ops,
                struct module *owner)

struct rtc_device *devm_rtc_device_register(struct device *dev,
          const char *name,
          const struct rtc_class_ops *ops,
          struct module *owner)
//注銷RTC      
static void rtc_device_unregister(struct rtc_device *rtc)     
void devm_rtc_device_unregister(struct device *dev, struct rtc_device *rtc)

總結

RTC也是字符設備驅動，只是進行了封裝，封裝完之后我們調用起來其實就很簡單了。只要實現好接口函數，填充好結構體，然后進行注冊即可。