void RTC_Configuration(void)
{
/* Enable PWR and BKP clocks */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);
/* Allow access to BKP Domain */
PWR_BackupAccessCmd(ENABLE);
/* Reset Backup Domain */
BKP_DeInit();
/* Enable LSE */
RCC_LSEConfig(RCC_LSE_ON);
/* Wait till LSE is ready */
while (RCC_GetFlagStatus(RCC_FLAG_LSERDY) == RESET)
{}
/* Select LSE as RTC Clock Source */
RCC_RTCCLKConfig(RCC_RTCCLKSource_LSE);
/* Enable RTC Clock */
RCC_RTCCLKCmd(ENABLE);
/* Wait for RTC registers synchronization */
RTC_WaitForSynchro();
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
/* Enable the RTC Second */
RTC_ITConfig(RTC_IT_SEC, ENABLE);
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
/* Set RTC prescaler: set RTC period to 1sec */
RTC_SetPrescaler(32767); /* RTC period = RTCCLK/RTC_PR = (32.768 KHz)/(32767+1) */
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
}



void StartRTC()
{
uint32_t min, hour;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);

PWR_BackupAccessCmd(ENABLE);
PWR_WakeUpPinCmd(DISABLE);
BKP_DeInit();
RCC_LSICmd(ENABLE);
while(RCC_GetFlagStatus(RCC_FLAG_LSIRDY) == RESET);
RCC_RTCCLKConfig(RCC_RTCCLKSource_LSI);
RCC_RTCCLKCmd(ENABLE);
RTC_WaitForSynchro();
RTC_SetPrescaler(32767);
RTC_WaitForLastTask();
RTC_SetCounter(0);
RTC_WaitForLastTask();
RTC_SetAlarm(1);
RTC_WaitForLastTask();
RTC_ITConfig(RTC_IT_ALR,ENABLE);
RTC_WaitForLastTask();
//PWR_EnterSTANDBYMode();
}

uint32_t SetElapsed(uint32_t e)
{
    PWR_BackupAccessCmd(ENABLE);
    RTC_SetCounter(e);
    RTC_WAITFORLASTTASK(1000);
    PWR_BackupAccessCmd(DISABLE); // else leave DBP bit set
    return GetElapsed();
}

RTC_SetCounter(0);