UM0290 datasheet(46/76 Pages) STMICROELECTRONICS

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Mass storage demo

UM0290

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For more information about the double buffer transfer mode please refer to the STR71x

reference manual.

5.3.3

Class specific requests

The Mass Storage Class specification describes two class specific requests:

Bulk-only Mass Storage reset

This request is used to reset the Mass Storage device and its associated interface. This

class specific request is to make the device ready for the next CBW sent by the PC host.

To issue the BOT Mass Storage Reset, the host issues a device request on the default pipe

(endpoint 0) of:

●

bmRequestType: Class, Interface, Host to device

●

bRequest field set to 0xFF

●

wValue field set to 0

●

wIndex field set to the interface number (0 for this implementation)

●

wLength field set to 0

This request is implemented as a no data class-specific request in the function

MASS_NoData_Setup()

(file usb_prop.c).

After receiving this request, the device clears the data toggle of the two bulk endpoints,

initializes the CBW signature to the default value and sets the BOT state machine to the

state BOT_IDLE to be ready to receive the next CBW.

GET MAX LUN request

A Mass Storage Device may implement several logical units that share common device

characteristics. The host uses bCBWLUN to designate which logical unit of the device is the

destination of the CBW.

The Get Max LUN device request is used to determine the number of logical units supported

by the device.

To issue a Get Max LUN request the host must issue a device request on the default pipe

(endpoint 0) of:

●

bmRequestType: Class, Interface, Host to device

●

bRequest field set to 0xFE

●

wValue field set to 0

●

wIndex field set to the interface number (0 for this implementation)

●

wLength field set to 1

This request is implemented as a Data class specific request in the function

MASS_Data_Setup()

(file usb_prop.c).

Note:

In the two implementations, there is only one LUN so the Get Max LUN is returned directly

with the Value 0x00. If the user wants to implement other LUNs he has to return the number

of implemented LUNs as response to this request.

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