5

7618C–AVR–07/08

4.3.2

DFU Configuration Descriptor

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

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

01h.

4.3.2.1

DFU 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.

Table 4-3.

DFU Mode Interface Description

Note:

1. Alternate settings can be used by an application to access additional memory segments. In this case, it is suggested that

each alternate setting employ a string descriptor to indicate the target memory segment; e.g., “EEPROM”. Details concern-

ing other possible uses of alternate settings are beyond the scope of this document. However, their use is intentionally not

restricted because the authors anticipate that implements will devise additional creative uses for alternate settings.

4.4

Commands Description

The protocol implemented in the AT90USB bootloader allows to:

• Initiate the communication

• Program the Flash or EEPROM Data

• Read the Flash or EEPROM Data

• Program Configuration Information

• Read Configuration and Manufacturer Information

• Erase the Flash

• Start the application

Overview of the protocol is detailed in “Appendix-A” on page 18.

15

iProduct

1

0

Index of string descriptor

16

iSerialNumber

1

0

Index of string descriptor

17

bNumConfigurations

1

01h

One configuration only for DFU

Offset

Field

Size

Value

Description

Offset

Field

Size

Value

Description

0

bLength

1

09h

Size of this descriptor, in bytes

1

bDescriptorType

1

04h

INTERFACE descriptor type

2

bInterfaceNumber

1

00h

Number of this interface

3

bAlternateSetting

1

00h

4

bNumEndpoints

1

00h

Only the control pipe is used

5

bInterfaceClass

1

FEh

Application Specific Class Code

6

bInterfaceSubClass

1

01h

Device Firmware Upgrade Code

7

bInterfaceProtocol

1

00h

The device does not use a class specific protocol on this interface

8

iInterface

1

00h

Index of the String descriptor for this interface