UM0290 datasheet(30/76 Pages) STMICROELECTRONICS

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Device firmware upgrade

UM0290

30/76

DFU mode configuration descriptor

This descriptor is identical to the standard configuration descriptor described in the USB

specification version 1.0, with the exception that the bNumInterfaces field must contain

the value 01h.

●

DFU Mode Interface Descriptor

This is the descriptor for the only interface available when operating in DFU mode.

Therefore, the value of the bInterfaceNumber field is always zero.

●

Alternate settings and string descriptor definition

This section describes the STMicroelectronics implementation for Alternate settings and the

corresponding string descriptor set that is not specified by the standard DFU specification in

section 4.2.3.

Alternate settings have to be used to access additional memory segments and other

memories (Flash memory, RAM, EEPROM) that may be physically implemented in the CPU

memory mapping or not, such as external serial SPI Flash memory or external NOR/NAND

Flash memory.

In this case, each alternate setting employs a string descriptor to indicate the target memory

segment as shown below:

@Target

Memory

Name/Start

Address/Sector(1)_Count*Sector(1)_Size

Sector(1)_Type,Sector(2)_Count*Sector(2)_SizeSector(2)_Type,......,

Sector(n)_Count*Sector(n)_SizeSector(n)_Type

Table 7.

DFU mode interface descriptor

Offset

Field

Size

Value

Description

bLength

09h

Size of this descriptor, in bytes.

bDescriptorType

04h

INTERFACE descriptor type.

bInterfaceNumber

00h

Number of this interface.

bAlternateSetting

Number

Alternate setting

bNumEndpoints

00h

Only the control pipe is used.

bInterfaceClass

FEh

Application Specific Class Code

bInterfaceSubClass

01h

Device Firmware Upgrade Code

bInterfaceProtocol

00h

The device does not use a class-specific

protocol on this interface

iInterface

Index

Index of string descriptor for this interface

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