stm32断电后时间不能保存是什么原因？

问题现象：
我用的芯片是 STM32F103VCT6，在VBAT脚加了3.3V电池，断电后，该引脚确实有电压
但是断电后，再上电，时间从新开始了，不能记录我之前修改好的
我看了一下寄存器，RTC_CNTH这个里面是用来存放断点之前的时钟数据的，但是断电之后再上电，这个里面的数据都没有了
但是软件复位就可以，依然有记录。
这是怎么回事呢？
void RTC_Configura tion(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 RTC_Config(void)
{
//l*** 2011.12.7 下面三句用来对BKP寄存器清0，缺一不可，只供实验用
//RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);

//Allow access to BKP Domain
//PWR_BackupAccessCmd(ENABLE);
//BKP_WriteBackupRegister(BKP_DR1, 0x0);
//BKP_WriteBackupRegister(BKP_DR1, 0x0);
//Reset Backup Domain
//2011.12.7

if (BKP_ReadBackupRegister(BKP_DR1) != 0xA5A5 )
{
//Backup data register value is not correct or not yet programmed (when the first time the program is executed)

// g_bNVRamBl=0; //电池电压低
//RTC Configuration
RTC_Configuration();

Os_InitTime(); //修改系统时间

BKP_WriteBackupRegister(BKP_DR1, 0xA5A5);
}
else
{
// g_bNVRamBl=1; //电池电压正常
//Check if the Power On Reset flag is set
if (RCC_GetFlagStatus(RCC_FLAG_PORRST) != RESET)
{
}
//Check if the Pin Reset flag is set
else if (RCC_GetFlagStatus(RCC_FLAG_PINRST) != RESET)
{
}
// Enable PWR and BKP clocks
RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);

//Allow access to BKP Domain
PWR_BackupAccessCmd(ENABLE);

Os_InitTime();

RTC_WaitForLastTask();
}

#ifdef RTCClockOutput_Enable
//Enable PWR and BKP clocks
RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);

//Allow access to BKP Domain
PWR_BackupAccessCmd(ENABLE);

//Disable the Tamper Pin
BKP_TamperPinCmd(DISABLE); //To output RTCCLK/64 on Tamper pin, the tamper
//functionality must be disabled

//Enable RTC Clock Output on Tamper Pin
BKP_RTCOutputConfig(BKP_RTCOutputSource_CalibClock);
#endif
//Clear reset flags
RCC_ClearFlag();
}
void Os_SetTime(TIME_S7* Time)
{
#if OS_CRITICAL_METHOD == 3 /* Storage for CPU status register */
OS_CPU_SR cpu_sr = 0;
#endif
u32 TimValue,IsLeap,i,DateNum=0;
OS_ENTER_CRITICAL();
sSysTime.Year = Time->Year;
sSysTime.Month = Time->Month;
sSysTime.Date = Time->Date;
sSysTime.Hour = Time->Hour;
sSysTime.Minute = Time->Minute;
sSysTime.Second = Time->Second;
sSysTime.MillSec = Time->MillSec;
IsLeap = IsLeapYear(&sSysTime);
if(IsLeap==0)
{
for(i=0;i Month;i++)
{
DateNum = DateNum + EachMonth[IsLeap] ;
}
TimValue=(sSysTime.Year-Ymark)*31536000+(DateNum+sSysTime.Date)*86400+sSysTime.Hour*3600
+ sSysTime.Minute*60 + sSysTime.Second+sSysTime.MillSec/1000;
}
else
{
for(i=0;i Month;i++)
{
DateNum = DateNum + EachMonth[IsLeap] ;
}
/* the value to store in RTC counter register */
TimValue=(sSysTime.Year-Ymark)*31622400+(DateNum+sSysTime.Date)*86400+sSysTime.Hour*3600
+ sSysTime.Minute*60 + sSysTime.Second+sSysTime.MillSec/1000;
}
/* Enable PWR and BKP clocks */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);
/* Allow access to BKP Domain */
PWR_BackupAccessCmd(ENABLE);
/* Change the current time */
RTC_SetCounter(TimValue);
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
// RTC_T_NUM = RTC_GetCounter();
// RTC_WaitForLastTask();
OS_EXIT_CRITICAL();
}

0