USB Mass Storage Class (MSC) Device

The USB device stack includes a mass storage interface for implementing the mass storage class. The interface handles all requests from the attached host and forwards all disk I/O operations to a specified disk driver.

Media Storage

The mass storage interface uses a disk driver for the physical storage of the file system data. A media disk driver is assigned to a logical unit when it is added to a mass storage interface. The mass storage interface does support multiple logical units (LUNs).

The media disk drivers provide status information about the physical disk, such as media presence and write protection, to the mass storage interface. The mass storage interface automatically provides this information to the host.

Basic Usage

The code snippet below shows how to initialize a USB device stack instance along with a mass storage class interface for a given media disk driver.

#include "USB/Device/usbd.h"
#include "USB/Device/usbd_msc.h"
#include <assert.h>

/* Define a block information transferred to an attached host */
const BYTE SCSIInfo[] = {

    0x00,                                           /* Direct-access block device */
    0x80,                                           /* Removable medium */
    0x00,                                           /* ISO, ECMA, and ANSI-approved versions */
    0x01,                                           /* AEC, TrmIOP, and Response data format */

    0x1F,                                           /* Additional length */
    0x00,
    0x00,
    0x00,

    'D', 'Z', 'X', ' ', ' ', ' ', ' ', ' ',         /* Vendor identification (ASCII) (bytes 8-15) */

    'S', 'D', ' ', 'D', 'I', 'S', 'K', ' ',         /* Product identification (ASCII) (bytes 16-31) */
    ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ',
	
    '1', '.', '0', ' '                              /* Product revision level (bytes 32-35) */
};

static USBDDEVICE usb;                              /* Allocate a USB device stack instance */
static MSCDINTERFACE massintf;                      /* Allocate a mass storage interface instance */
static MSCDLUN lun;                                 /* Allocate a mass storage logical unit (LUN) */


void APP_InitMSC(DISK* disk)
{
    STATUS status;

                            
    status = USBD_Create(&usb,                      /* Create and initialize the USB device stack */
                         0,                         /* Port number */
                         0x0000,                    /* Device vendor ID */
                         0x0001);                   /* Device product ID */
    assert(status == SUCCESS);

    status = USBD_SetDeviceName(&usb,               /* Assign text names to the usb device */
                                "DZX",              /* Manufacturer name */
                                "MSC Demo",         /* Product name */
                                "123456789ABCD",    /* Serial number */
    assert(status == SUCCESS);

    status = MSCD_CreateInterface(&usb,             /* Create and initialize the mass storage interface */
                                  &massintf,        /* A pointer to the mass storage interface */
                                  0x01);            /* Logical endpoint number used by the interface */
    assert(status == SUCCESS);

    status = MSCD_AddLUN(&massintf,                 /* Add a logical unit to the mass storage interface */
                         &lun,                      /* A pointer to the logical unit instance to be initialized */
                         &disk.base,                /* A pointer to the media storage disk to handle I/O operations */
                         SCSIInfo,                  /* A pointer to the SCSI info */
                         sizeof(SCSIInfo));         /* Size, in bytes, of the SCSI info */
    assert(status == SUCCESS);

    status = USBD_Open(&usb);                       /* Enable USB device communications */
    assert(status == SUCCESS);
}