stm32 flash读保护失效问题

stm32 flash可以设置三个级别的读保护，实现读保护以后，flash将不可以从外部读取，如果想再次烧录代码，需要解除保护，解除读保护也可以使用代码，例如在代码中添加触发机制，比如串口收到某个特殊字符，则调用函数解除读保护。又或者使用软件，依然还是STM32 ST-LINK Utiltity，操作过程和打开读保护一致，只不过在选择等级的时候选择Level 0，则会将flash上的数据全部擦除，接着就可以重新烧代码。

读保护、关闭保护代码实现

在调试代码前，需要先了解怎样擦除读保护（isp\jlink\ram启动 解除保护）

/****************************************************************
 * Function:    Flash_EnableReadProtection
 * Description: Enable the read protection of user flash area.
 * Input:
 * Output:
 * Return:      1: Read Protection successfully enable
 *              2: Error: Flash read unprotection failed
*****************************************************************/
uint32_t Flash_EnableReadProtection(void)
{
  /* Returns the FLASH Read Protection level. */
  if( FLASH_OB_GetRDP() == RESET )
  {
    /* Unlock the Option Bytes */
    FLASH_OB_Unlock();
    
    /* Sets the read protection level. */
    FLASH_OB_RDPConfig(OB_RDP_Level_1);
    
    /* Start the Option Bytes programming process. */  
    if (FLASH_OB_Launch() != FLASH_COMPLETE)
    {
      /* Disable the Flash option control register access (recommended to protect 
         the option Bytes against possible unwanted operations) */
      FLASH_OB_Lock();
      
      /* Error: Flash read unprotection failed */
      return (2);
    }
  
    /* Disable the Flash option control register access (recommended to protect 
       the option Bytes against possible unwanted operations) */
    FLASH_OB_Lock();
 
    /* Read Protection successfully enable */
    return (1);
  }
  
  /* Read Protection successfully enable */
  return (1);
}
 
/****************************************************************
 * Function:    Flash_DisableReadProtection
 * Description: Disable the read protection of user flash area.
 * Input:
 * Output:
 * Return:      1: Read Protection successfully disable
 *              2: Error: Flash read unprotection failed
*****************************************************************/
uint32_t Flash_DisableReadProtection(void)
{
  /* Returns the FLASH Read Protection level. */
  if( FLASH_OB_GetRDP() != RESET )
  {
    /* Unlock the Option Bytes */
    FLASH_OB_Unlock();
    
    /* Sets the read protection level. */
    FLASH_OB_RDPConfig(OB_RDP_Level_0);
    
    /* Start the Option Bytes programming process. */  
    if (FLASH_OB_Launch() != FLASH_COMPLETE)
    {
      /* Disable the Flash option control register access (recommended to protect 
         the option Bytes against possible unwanted operations) */
      FLASH_OB_Lock();
      
      /* Error: Flash read unprotection failed */
      return (2);
    }
  
    /* Disable the Flash option control register access (recommended to protect 
       the option Bytes against possible unwanted operations) */
    FLASH_OB_Lock();
 
    /* Read Protection successfully disable */
    return (1);
  }
  
  /* Read Protection successfully disable */
  return (1);
}

在main开始后加入Flash_EnableReadProtection（）；即可实现读保护。在内部后台调用Flash_DisableReadProtection（）解除保护。

• 在烧录前需要确保程序内无其他解除保护代码
• 烧录后需要掉电重启以运行程序（保护选项会在上电后自动载入一次）