更新BootLoader为USB传输，替代V1版本中的usart

bootloader/Ymodem/flash_if.h

@@ -51,6 +51,18 @@
    Note: the 1st sector 0x08000000-0x08003FFF is reserved for the IAP code */
 #define APPLICATION_ADDRESS   (uint32_t)0x0800C000
 
+/* Exported types ------------------------------------------------------------*/
+
+#define UPGRADE_INFO_ADDRESS          (USER_FLASH_END_ADDRESS - sizeof(UpgradeInfo_t) + 1)
+// 定义升级信息结构体
+typedef struct {
+    uint32_t magic_word;      // 魔法字，如 0xDEADBEEF，用于标识此结构体有效
+    uint32_t upgrade_status;  // 升级状态标志
+    uint32_t new_app_size;    // 新APP的固件大小
+    uint32_t new_app_crc32;   // 新APP的CRC32校验和
+} UpgradeInfo_t;
+
+
 /* Exported macro ------------------------------------------------------------*/
 /* Exported functions ------------------------------------------------------- */
 void FLASH_If_Init(void);