STM32的flash数据页转存过程分析！

stm32模拟eeprom要实现flash数据页转存，实现函数为

/**
* @brief Transfers last updated variables data from the full Page to
* an empty one.
* @param VirtAddress: 16 bit virtual address of the variable
* @param Data: 16 bit data to be written as variable value
* @retval Success or error status:
* - FLASH_COMPLETE: on success
* - PAGE_FULL: if valid page is full
* - NO_VALID_PAGE: if no valid page was found
* - Flash error code: on write Flash error
*/
uint16_t EE_PageTransfer(uint16_t VirtAddress, uint16_t Data)

这个函数的过程为：

1. 得到当前可读有效页，并设置其为oldPage，另一页为NewPage。

2. 给NewPage设置RECEIVE_DATA状态

3.初始化写地址 切换到接收页

4. 写一个当前要保存的数据，如果单纯发起一次转存，则随意保存一个数据。

5. 读出除第三步保存过的所有要保存的变量数据，保存到NewPage中。

6. 擦除OldPage（执行时间15ms-2s，根据扇区大小而定（1K~128K））

7. 给NewPage设置VALID_PAGE状态。

第5步中 Get the valid Page end Address 

if((PageStatus0 == RECEIVE_DATA)||(PageStatus1 == RECEIVE_DATA))//当页传输的时候把valid Page end Address切换到可读有效页的最后
{
     Address = (uint32_t)((EEPROM_START_ADDRESS - 2) + (uint32_t)((1 + ValidPage) * PAGE_SIZE));
 }
 else
 {
     Address=CurWrAddress-2;
 }

转存完成后的各页的状态：NewPage:VALID_PAGE;

　　　　　　　　　　　  OldPage:ERASED;

但是在转存过程中系统断电，则各页的状态可能出现

1.NewPage:ERASED; OldPage:VALID_PAGE; 这种情况发生在EE_PageTransfer函数执行到第二步之前系统掉电。那么这次转存过程就当没有发生过，要保存的那个数据变量也得不到保存。

2.NewPage:RECEIVE_DATA; OldPage:VALID_PAGE; 这种情况发生在EE_PageTransfer函数执行到第六步之前系统掉电。

3.NewPage:RECEIVE_DATA; OldPage:ERASED; 这种情况发生第六步执行过程中系统掉电。

主要讨论第2、3中情况下开机初始化eeprom的时候处 

 1 //NewPage:RECEIVE_DATA; OldPage:VALID_PAGE; 2 InitCurrWrAddress();//初始化写地址
 2 //这里NewPage为PAGE1 OldPage为Page0
 3                   
  /* Transfer data from Page0 to Page1 */
  for (VarIdx = 0; VarIdx < NumbOfVar; VarIdx++)
  {
     if ((*(__IO uint16_t*)(PAGE1_BASE_ADDRESS + 6)) == VirtAddVarTab[VarIdx])
     {
          x = VarIdx;
     }
     if (VarIdx != x)
     {
         /* Read the last variables' updates */
          ReadStatus = EE_ReadVariable(VirtAddVarTab[VarIdx], &DataVar);
           /* In case variable corresponding to the virtual address was found */
          if (ReadStatus != 0x1)
          {
         　　/* Transfer the variable to the Page1 */
         　　 EepromStatus =     EE_VerifyPageFullWriteVariable(VirtAddVarTab[VarIdx], DataVar);
            /* If program operation was failed, a Flash error code is returned */
           if (EepromStatus != FLASH_COMPLETE)
           {
       　　　　　return EepromStatus;
           }
         }
     }
 }//for (VarIdx...
 /* Mark Page1 as valid */
 FlashStatus = FLASH_ProgramHalfWord(PAGE1_BASE_ADDRESS, VALID_PAGE);
 /* If program operation was failed, a Flash error code is returned */
 if (FlashStatus != FLASH_COMPLETE)
 {
     return FlashStatus;
 }
/* Erase Page0 */
FlashStatus = FLASH_EraseSector(PAGE0_ID, VOLTAGE_RANGE);
/* If erase operation was failed, a Flash error code is returned */
if (FlashStatus != FLASH_COMPLETE)
{
   return FlashStatus;
}

过程：

1.读出除第一个位置保存过的所有要保存的变量数据，保存到NewPage中。

2. 把RECEIVE_DATA状态改为VALID_PAGE

3. 擦除OldPage。

  //NewPage:RECEIVE_DATA; OldPage:ERASED;OldPage:Page0 NewPage:Page1
  /* Erase Page0 */
  FlashStatus = FLASH_EraseSector(PAGE0_ID, VOLTAGE_RANGE);
  /* If erase operation was failed, a Flash error code is returned */
  if (FlashStatus != FLASH_COMPLETE)
  {
     return FlashStatus;
  }
  /* Mark Page1 as valid */
 FlashStatus = FLASH_ProgramHalfWord(PAGE1_BASE_ADDRESS,VALID_PAGE);
 /* If program operation was failed, a Flash error code is returned */
 if (FlashStatus != FLASH_COMPLETE)
 {
    return FlashStatus;
 }

第三种情况下

1. 擦除OldPage

2. 把RECEIVE_DATA状态改为VALID_PAGE