stm32 RTC用法

stm32的RTC时钟源有三个方式（截图来源正点原子资料）

1.HSE分频过来

2.LSE 32.768K晶体

3.LSI内部RC振荡器

下面示例采用的是HSE时钟源

1.RTC时钟源配置

#define RTC_CLOCK_SOURCE_HSE
#define RTC_FLAG_BKP  1

__IO uint32_t AsynchPrediv = 0, SynchPrediv = 0;

void RTC_Config(void)
{

#if defined (RTC_CLOCK_SOURCE_LSI)  /* LSI used as RTC source clock*/
	/* The RTC Clock may varies due to LSI frequency dispersion. */   
	/* Enable the LSI OSC */ 
	RCC_LSICmd(ENABLE);

	/* Wait till LSI is ready */  
	while(RCC_GetFlagStatus(RCC_FLAG_LSIRDY) == RESET)
	{
	}

	/* Select the RTC Clock Source */
	RCC_RTCCLKConfig(RCC_RTCCLKSource_LSI);

/*40khz  (0x18f+1)*(0x63+1)=40k */
	SynchPrediv = 0x18F;
	AsynchPrediv = 0x63;

#elif defined (RTC_CLOCK_SOURCE_LSE) /* LSE used as RTC source clock */
	/* Enable the LSE OSC */
	RCC_LSEConfig(RCC_LSE_ON);

	/* Wait till LSE is ready */  
	while(RCC_GetFlagStatus(RCC_FLAG_LSERDY) == RESET)
	{
	}

	/* Select the RTC Clock Source */
	RCC_RTCCLKConfig(RCC_RTCCLKSource_LSE);
	
/*32.768khz  (0xff+1)*(0x7f+1)=32.768k */
	SynchPrediv = 0xFF;
	AsynchPrediv = 0x7F;
	
#elif defined(RTC_CLOCK_SOURCE_HSE)
	RCC_HSEConfig(RCC_HSE_ON);

		/* Wait till HSE is ready */  
	while(RCC_GetFlagStatus(RCC_FLAG_HSERDY) == RESET)
	{
	}
	
/*外部晶振8M, 32分频 8M/32=250K*/
	RCC_RTCCLKConfig(RCC_RTCCLKSource_HSE_Div32);

/*250khz  (2499+1)*(99+1)=250k */
	SynchPrediv = 	2499;
	AsynchPrediv = 99;
	
#else
#error Please select the RTC Clock source inside the main.c file
#endif /* RTC_CLOCK_SOURCE_LSI */

	/* Enable the RTC Clock */
	RCC_RTCCLKCmd(ENABLE);

	/* Wait for RTC APB registers synchronisation */
	RTC_WaitForSynchro();
}

2.初始化RTC

void RTC_init(void)
{
	RTC_InitTypeDef RTC_InitStructure;
	RTC_TimeTypeDef  RTC_TimeStruct;	

	/* Enable the PWR clock */
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);

	/* Allow access to RTC */
	PWR_BackupAccessCmd(ENABLE);

	if(RTC_ReadBackupRegister(RTC_BKP_DR0) != RTC_FLAG_BKP)
	{
		/* RTC configuration  */
		RTC_Config();

		/* Configure the RTC data register and RTC prescaler */
		RTC_InitStructure.RTC_AsynchPrediv = AsynchPrediv;
		RTC_InitStructure.RTC_SynchPrediv = SynchPrediv;
		RTC_InitStructure.RTC_HourFormat = RTC_HourFormat_24;

		/* Check on RTC init */
		if (RTC_Init(&RTC_InitStructure) == ERROR)
		{
		  printf("\n\r        /!\\***** RTC Prescaler Config failed ********/!\\ \n\r");
		}

		  /* Set the time to 00h 00mn 00s AM */
		RTC_TimeStruct.RTC_H12     = RTC_H12_AM;
		RTC_TimeStruct.RTC_Hours   = 0x00;
		RTC_TimeStruct.RTC_Minutes = 0x00;
		RTC_TimeStruct.RTC_Seconds = 0x00;  
		RTC_SetTime(RTC_Format_BCD, &RTC_TimeStruct);
	  
	    	RTC_WriteBackupRegister(RTC_BKP_DR0, RTC_FLAG_BKP);
	}
	else
	{
		#ifdef RTC_CLOCK_SOURCE_LSI
	    	RCC_LSICmd(ENABLE);
		#endif

	    	RTC_WaitForSynchro();                            /*等待RTC与RTC_APB时钟同步*/
	}
}

RTC初始化完成，应用就可以

RTC_GetTime

RTC_GetDate

RTC_SetTime

RTC_SetDate

获取和设置日期和时间了。

样例采用的是HSE时钟源，RTC的误差非常小（几天才几秒，取决于外部晶体精度），如果是HEI时钟源，误差可能1天几分钟甚至几十分钟。

STM32时钟详细介绍参见http://bbs.elecfans.com/forum.php?mod=viewthread&tid=388275

感谢您的关注，承接STM32 + MC20/EC20/M5311的开发项目（Q190109829）