Posted on November 22, 2011 at 20:35You'll need different RTC initialization code paths based on the type of reset (power-on, standby, etc). For example there is clearly no point starting up and waiting for the LSE if it is already running. Take a look at some of the example code, it is really worth reviewing before coding randomly. Personally I find the STANDBY model to turn things off works significantly better than just killing the supply.
void RTC_Configuration(void)
{
/* Check if the StandBy flag is set */
if(PWR_GetFlagStatus(PWR_FLAG_SB) != RESET)
{/* System resumed from STANDBY mode */
/* Turn on led connected to GPIO_LED Pin7 */
GPIO_SetBits(GPIO_LED, GPIO_Pin_7);
/* Clear StandBy flag */
PWR_ClearFlag(PWR_FLAG_SB);
/* Wait for RTC APB registers synchronisation */
RTC_WaitForSynchro();
/* No need to configure the RTC as the RTC configuration(clock source, enable,
prescaler,...) is kept after wake-up from STANDBY */
}
else
{/* StandBy flag is not set */
/* RTC clock source configuration ----------------------------------------*/
/* Reset Backup Domain */
BKP_DeInit();
/* Enable 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);
/* Enable the RTC Clock */
RCC_RTCCLKCmd(ENABLE);
/* RTC configuration -----------------------------------------------------*/
/* Wait for RTC APB registers synchronisation */
RTC_WaitForSynchro();
/* Set the RTC time base to 1s */
RTC_SetPrescaler(32767);
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
}
}
/* Enable PWR and BKP clock */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);
/* Enable WKUP pin */
PWR_WakeUpPinCmd(ENABLE);
/* Allow access to BKP Domain */
PWR_BackupAccessCmd(ENABLE);
/* Configure RTC clock source and prescaler */
RTC_Configuration();
