基于FAT的USB疑问
笔者使用硬石例程78（F4系列）基于FAT的USB HOST工程代码，在阅读代码时发现一个问题如下：在文件ff_gen_drv.h中定义了结构体Diskio_drvTypeDef和Disk_drvTypeDef：typedef struct{ DSTATUS (*disk_initialize) (BYTE); /*!< Initialize Disk Drive */ DSTATUS (*disk_status) (BYTE); /*!< Get Disk Status */ DRESULT (*disk_read) (BYTE,BYTE*, DWORD, UINT); /*!< ReadSector(s) */#if _USE_WRITE == 1 DRESULT (*disk_write) (BYTE,const BYTE*, DWORD, UINT); /*!< Write Sector(s) when _USE_WRITE = 0 */#endif /* _USE_WRITE == 1 */#if _USE_IOCTL == 1 DRESULT (*disk_ioctl) (BYTE,BYTE, void*); /*!< I/O control operation when _USE_IOCTL= 1 */#endif /* _USE_IOCTL == 1 */}Diskio_drvTypeDef;/** *@briefGlobal Disk IO Drivers structuredefinition*/ typedef struct{ uint8_t is_initialized; Diskio_drvTypeDef *drv; uint8_t lun; __IO uint8_t nbr;}Disk_drvTypeDef;在文件usbh_diskio.c中初始化了结构体Diskio_drvTypeDef：const Diskio_drvTypeDefUSBH_Driver ={ USBH_initialize, USBH_status, USBH_read, #if _USE_WRITE == 1 USBH_write,#endif /* _USE_WRITE == 1 */#if _USE_IOCTL == 1 USBH_ioctl,#endif /* _USE_IOCTL == 1 */};现在的问题是，在主程序中使用了f_read函数，而f_read函数调用了disk_read函数，而在disk_read函数中有如下语句：res =disk.drv->disk_read(disk.lun, buff, sector, count);但是经过程序仿真跟踪发现，上句真正执行的函数是usbh_diskio.c中USBH_read函数。上述的原因是什么？
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