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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：
- Data EEPROM Bank1: 0x08080000 ~ 0x08081FFF (8KB)
- Data EEPROM Bank2: 0x08082000 ~ 0x08083FFF (8KB)
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。
- Write PEKEY1= 0x89ABCDEF to the Program/erase key register (FLASH_PEKEYR)
- Write PEKEY2= 0x02030405 to the Program/erase key register (FLASH_PEKEYR)
/*** @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_PEKEY2to unlock the write access to the FLASH_PECR register anddata 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：
- Word 和 double word 擦除
- Mass 擦除
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：
- unlock
- erase
- write
- lock
/*** @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：
- 尽量以 4 字节为一个单位进行操作
- 在执行写入或者擦除操作的时候，尽量将全局中断关闭，以免中断触发引起其它的问题
- 不要对相同的一个 Bank 同时做多种操作，尽量保证一个 Bank 只有一种操作在执行
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);
}