UM0290 datasheet(28/76 Pages) STMICROELECTRONICS

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Device firmware upgrade

UM0290

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4.3

DFU mode selection

The host should be able to enumerate a device with DFU capability in two ways:

●

as a single device with only DFU capability

●

as a composite device: HID, Mass storage, or any functional class, and with DFU

capability.

During the enumeration phase, the device exposes two distinct and independent descriptor

sets, each one at the appropriate time:

●

Run-time descriptor set: shown when the device performs normal operations

●

DFU mode descriptor set: shown when host and device agree to perform DFU

operations

4.3.1

Run-time descriptor set

During normal run-time operation, the device exposes its normal set of descriptors plus two

additional descriptors:

●

Run-Time DFU Interface descriptor

●

Run-Time DFU Functional descriptor

Note:

The number of interfaces in each configuration descriptor that supports the DFU must be

incremented by one to accommodate the addition of the DFU interface descriptor.

4.3.2

DFU mode descriptor set

After the host and the device agree to perform DFU operations, the host re-enumerates the

device. At this time the device exports the descriptor set shown below:

●

DFU Mode Device descriptor

●

DFU Mode Configuration descriptor

●

DFU Mode Interface descriptor

●

DFU Mode Functional descriptor: identical to the Run-Time DFU Functional descriptor

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