这是库自带的stm32f2xx_RTC.c,单步仿真发现 tmpreg =0x00170800  计算出来的日期是17年8月0号，
正确日期是7月31号，其他的时间小时分钟秒都是对的，有谁遇到过类似的吗？


/**
  * @brief  Get the RTC current date.
  * @param  RTC_Format: specifies the format of the returned parameters.
  *          This parameter can be one of the following values:
  *            @arg RTC_Format_BIN: Binary data format
  *            @arg RTC_Format_BCD: BCD data format
  * @param RTC_DateStruct: pointer to a RTC_DateTypeDef structure that will
  *                        contain the returned current date configuration.     
  * @retval None
  */
void RTC_GetDate(uint32_t RTC_Format, RTC_DateTypeDef* RTC_DateStruct)
{
  uint32_t tmpreg = 0;

  /* Check the parameters */
  assert_param(IS_RTC_FORMAT(RTC_Format));
  
  /* Get the RTC_TR register */
  tmpreg = (uint32_t)(RTC->DR & RTC_DR_RESERVED_MASK);

  /* Fill the structure fields with the read parameters */
  RTC_DateStruct->RTC_Year = (uint8_t)((tmpreg & (RTC_DR_YT | RTC_DR_YU)) >> 16);
  RTC_DateStruct->RTC_Month = (uint8_t)((tmpreg & (RTC_DR_MT | RTC_DR_MU)) >> 8);
  RTC_DateStruct->RTC_Date = (uint8_t)(tmpreg & (RTC_DR_DT | RTC_DR_DU));
  RTC_DateStruct->RTC_WeekDay = (uint8_t)((tmpreg & (RTC_DR_WDU)) >> 13);  

  /* Check the input parameters format */
  if (RTC_Format == RTC_Format_BIN)
  {
    /* Convert the structure parameters to Binary format */
    RTC_DateStruct->RTC_Year = (uint8_t)RTC_Bcd2ToByte(RTC_DateStruct->RTC_Year);
    RTC_DateStruct->RTC_Month = (uint8_t)RTC_Bcd2ToByte(RTC_DateStruct->RTC_Month);
    RTC_DateStruct->RTC_Date = (uint8_t)RTC_Bcd2ToByte(RTC_DateStruct->RTC_Date);
    RTC_DateStruct->RTC_WeekDay = (uint8_t)(RTC_DateStruct->RTC_WeekDay);   
  }
}