arduino中time.h的使用方法

官方文档地址：https://playground.arduino.cc/Code/Time/

1. 变量类型

首先，在TimeLib.h中，定义了
typedef unsigned long time_t;
time_t 的取值范围0~4294967295，表示的是1970年1月1日以来的秒数。

2. 主要函数

int     hour();            // the hour now 
int     hour(time_t t);    // the hour for the given time
int     hourFormat12();    // the hour now in 12 hour format
int     hourFormat12(time_t t); // the hour for the given time in 12 hour format
uint8_t isAM();            // returns true if time now is AM
uint8_t isAM(time_t t);    // returns true the given time is AM
uint8_t isPM();            // returns true if time now is PM
uint8_t isPM(time_t t);    // returns true the given time is PM
int     minute();          // the minute now 
int     minute(time_t t);  // the minute for the given time
int     second();          // the second now 
int     second(time_t t);  // the second for the given time
int     day();             // the day now 
int     day(time_t t);     // the day for the given time
int     weekday();         // the weekday now (Sunday is day 1) 
int     weekday(time_t t); // the weekday for the given time 
int     month();           // the month now  (Jan is month 1)
int     month(time_t t);   // the month for the given time
int     year();            // the full four digit year: (2009, 2010 etc) 
int     year(time_t t);    // the year for the given time

3. 设置系统时间

设置系统时间的方法有两种，一种用秒数，另一种是使用年月日等多个参数。

void setTime(time_t t) { 
#ifdef TIME_DRIFT_INFO
 if(sysUnsyncedTime == 0) 
   sysUnsyncedTime = t;   // store the time of the first call to set a valid Time   
#endif

  sysTime = (uint32_t)t;  
  nextSyncTime = (uint32_t)t + syncInterval;
  Status = timeSet;
  prevMillis = millis();  // restart counting from now (thanks to Korman for this fix)
} 

void setTime(int hr,int min,int sec,int dy, int mnth, int yr){
 // year can be given as full four digit year or two digts (2010 or 10 for 2010);  
 //it is converted to years since 1970
  if( yr > 99)
      yr = yr - 1970;
  else
      yr += 30;  
  tm.Year = yr;
  tm.Month = mnth;
  tm.Day = dy;
  tm.Hour = hr;
  tm.Minute = min;
  tm.Second = sec;
  setTime(makeTime(tm));
}

在与ds1307的通讯中，又使用了下面的方法

 setSyncProvider(RTC.get);   // the function to get the time from the RTC
void setSyncProvider( getExternalTime getTimeFunction){
  getTimePtr = getTimeFunction;  
  nextSyncTime = sysTime;
  now(); // this will sync the clock
}