STM32内部EEPROM读写操作详解

STM32 的某些系列 MCU 自带 EEPROM。笔者使用的 STM32L151RET6 自带 16 KB 的 EEPROM，可以用来存储自定义的数据。在芯片选型时，自带 EEPROM 也可以作为一个考量点，省去了在外接 EEPROM 的烦恼。

下面简单介绍下 STM32 内部 EEPROM 的读写流程。

Memory Mapping

以笔者使用的这款 STM32L151RET6 MCU 为例，自带 16 KB 的 EEPROM。Map 到了 2 个 Bank 中：

Operations

内部 EEPROM 的操作无非就是 读取、写入、擦除 等操作。直接调用库函数或者 HAL 库中对应的 API 即可。这里只是对内部 EEPROM 的操作做一个简要的分析。

本文档主要以库函数中的 EEPROM 接口 API 进行分析。

Unlocking/locking memory

STM32 复位后，Data EEPROM 和 Program/erase 控制寄存器 (FLASH_PECR) 默认是 处于 lock 状态，需要 unlock 之后才能执行写入和擦除操作。

如何 unlock 可以参考芯片对应的 datasheet，简单的说就是往 Program/erase 密钥寄存器 (FLASH_PEKEYR) 写指定的密钥集即可。

/**
  * @brief  Unlocks the data memory and FLASH_PECR register access.
  * @param  None
  * @retval None
  */
void DATA_EEPROM_Unlock(void)
{
  if((FLASH->PECR & FLASH_PECR_PELOCK) != RESET)
  {  
    /* Unlocking the Data memory and FLASH_PECR register access*/
    FLASH->PEKEYR = FLASH_PEKEY1;
    FLASH->PEKEYR = FLASH_PEKEY2;
  }
}

#define FLASH_PEKEY1               ((uint32_t)0x89ABCDEF) /*!< Flash program erase key1 */
#define FLASH_PEKEY2               ((uint32_t)0x02030405) /*!< Flash program erase key: used with FLASH_PEKEY2
                                                               to unlock the write access to the FLASH_PECR register and
                                                               data EEPROM */

如何 lock 可以参考芯片对应的 datasheet，相较于 unlock，lock 仅需要置位 Program/erase 控制寄存器 (FLASH_PECR) 中的 FLASH_PECR 位。

/**
  * @brief  Locks the Data memory and FLASH_PECR register access.
  * @param  None
  * @retval None
  */
void DATA_EEPROM_Lock(void)
{
  /* Set the PELOCK Bit to lock the data memory and FLASH_PECR register access */
  FLASH->PECR |= FLASH_PECR_PELOCK;
}

Erasing memory

对于 EEPROM，支持以下 2 种擦除方式：

对于 Word 和 double word 擦除，这种方式仅针对 EEPROM；但是对于 Mass 擦除，这种方式针对 Program memory、EEPROM 和 Option bytes。所以尽量在使用 EEPROM 的时候采用 Word 和 double word 擦除方式。

EEPROM 擦除方式也很简单，只需要将值 0x00000000 写入到对应的有效的擦除地址中即可。

/**
  * @brief  Erase a word in data memory.
  * @param  Address: specifies the address to be erased.
  * @note   For STM32L1XX_MD, A data memory word is erased in the data memory only 
  *         if the address to load is the start address of a word (multiple of a word).
  * @note   To correctly run this function, the DATA_EEPROM_Unlock() function
  *         must be called before.
  *         Call the DATA_EEPROM_Lock() to disable the data EEPROM access
  *         and Flash program erase control register access(recommended to protect 
  *         the DATA_EEPROM against possible unwanted operation).
  * @retval FLASH Status: The returned value can be: 
  *   FLASH_ERROR_PROGRAM, FLASH_ERROR_WRP, FLASH_COMPLETE or FLASH_TIMEOUT.
  */
FLASH_Status DATA_EEPROM_EraseWord(uint32_t Address)
{
  FLASH_Status status = FLASH_COMPLETE;
  
  /* Check the parameters */
  assert_param(IS_FLASH_DATA_ADDRESS(Address));
  
  /* Wait for last operation to be completed */
  status = FLASH_WaitForLastOperation(FLASH_ER_PRG_TIMEOUT);
  
  if(status == FLASH_COMPLETE)
  {
    /* Write "00000000h" to valid address in the data memory" */
    *(__IO uint32_t *) Address = 0x00000000;
  }
   
  /* Return the erase status */
  return status;
}

Programming memory

写入 EEPROM 的步骤也很简单，一般的流程如下：

/**
  * @brief  Programs a word at a specified address in data memory without erase.
  * @note   To correctly run this function, the DATA_EEPROM_Unlock() function
  *         must be called before.
  *         Call the DATA_EEPROM_Lock() to disable the data EEPROM access
  *         and Flash program erase control register access(recommended to protect 
  *         the DATA_EEPROM against possible unwanted operation).
  * @note   The function  DATA_EEPROM_FixedTimeProgramCmd() can be called before 
  *         this function to configure the Fixed Time Programming.
  * @param  Address: specifies the address to be written.
  * @param  Data: specifies the data to be written.
  * @retval FLASH Status: The returned value can be:
  *   FLASH_ERROR_PROGRAM, FLASH_ERROR_WRP, FLASH_COMPLETE or  FLASH_TIMEOUT. 
  */
FLASH_Status DATA_EEPROM_ProgramWord(uint32_t Address, uint32_t Data)
{
  FLASH_Status status = FLASH_COMPLETE;
  
  /* Check the parameters */
  assert_param(IS_FLASH_DATA_ADDRESS(Address));
  
  /* Wait for last operation to be completed */
  status = FLASH_WaitForLastOperation(FLASH_ER_PRG_TIMEOUT);
  
  if(status == FLASH_COMPLETE)
  {
    *(__IO uint32_t *)Address = Data;

    /* Wait for last operation to be completed */
    status = FLASH_WaitForLastOperation(FLASH_ER_PRG_TIMEOUT);
  }
  /* Return the Write Status */
  return status;
}

Reading Momory

读取 EEPROM 中的数据就没那么多步骤了，直接读取对应的 Map 的 Bank 即可。

Note

对于 EEPROM 的操作，以下几点需要注意：

列出一段 EEPROM 的参考代码：

void EEPROM_Test(void)
{
	__set_PRIMASK(1);

	DATA_EEPROM_Unlock();

	/* EEPROM Operations */

	DATA_EEPROM_Lock();

	__set_PRIMASK(0);
}