MSC Configuration

General Configuration

Class Instance Configuration

Before starting the communication phase, your application needs to initialize and configure the class to suit its needs. Table - Class Instance API Functions summarizes the initialization functions provided by the MSC implementation. Please refer to the MSC Functions reference for a full listing of the MSC API.

To successfully initialize the MSC, you need to follow these steps:

1. Call USBD_MSC_Init()
   This is the first function you should call, and it should be called only once regardless of the number of class instances you intend to have. This function will initialize all internal structures and variables that the class will need. It will also initialize the real-time operating system (RTOS) layer.
2. Call USBD_MSC_Add()
   This function will add a new instance of the MSC.
3. Call USBD_MSC_CfgAdd()
   Once the class instance is correctly configured and initialized, you will need to add it to a USB configuration. High speed devices will build two separate configurations, one for full speed and one for high speed by calling USBD_MSC_CfgAdd() for each speed configuration.
4. Call USBD_MSC_LunAdd()

Lastly, you add a logical unit to the MSC interface by calling this function. You will specify the type and volume of the logical unit you want to add as well as device details such as vendor ID string, product ID string, product revision level and read only flag. Logical units are identified by a string name composed of the storage device driver name and the logical unit number as follows: <device_driver_name>:<logical_unit_number>:. The logical unit number starts counting from number 0. For example, if a device has only one logical unit, the <logical_unit_number> specified in this field should be 0. Examples of logical units string name are ram:0:, sdcard:0:, etc. This function is called several times when a multiple logical unit configuration is created.

Listing - MSC Initialization shows how the latter functions are called during MSC initialization and an example of multiple logical units initialization.

USBD_ERR     err;
CPU_INT08U   msc_nbr;
CPU_BOOLEAN  valid;


USBD_MSC_Init(&err);                                                          (1)
if (err != USBD_ERR_NONE){
    return (DEF_FAIL);
}
 
msc_nbr = USBD_MSC_Add(&err);                                                 (2)
if (cfg_hs != USBD_CFG_NBR_NONE){
    valid = USBD_MSC_CfgAdd(msc_nbr,                                          (3)
                            dev_nbr,
                            cfg_hs,
                           &err);
    if (valid != DEF_YES) {
        return (DEF_FAIL);
    }
}
 
if (cfg_fs != USBD_CFG_NBR_NONE){
    valid = USBD_MSC_CfgAdd(msc_nbr,                                          (4)
                            dev_nbr,
                            cfg_fs,
                           &err);
    if (valid != DEF_YES) {
        return (DEF_FAIL);
    }
}

USBD_MSC_LunAdd((void *)"ram:0:",                                             (5)
                         msc_nbr,
                        "Micrium",
                        "MSC LUN 0 RAM",
                         0x0000,
                         DEF_TRUE,
                        &err);
if (err != USBD_ERR_NONE){
    return (DEF_FAIL);
}

USBD_MSC_LunAdd((void *)"sdcard:0:",                                          (6)
                         msc_nbr,
                        "Micrium",
                        "MSC LUN 1 SD",
                         0x0000,
                         DEF_FALSE,
                        &err);
if (err != USBD_ERR_NONE){
    return (DEF_FAIL);
}

return (DEF_OK);