UM0290 datasheet(27/76 Pages) STMICROELECTRONICS

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UM0290

Device firmware upgrade

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4.2.2

Phases

There are four distinct phases required to accomplish a firmware upgrade:

Enumeration: The device informs the host of its capabilities. A DFU class-interface

descriptor and associated functional descriptor embedded within the device’s normal

run-time descriptors serve this purpose and provide a target for class-specific requests

over the control pipe.

DFU Enumeration: The host and the device agree to initiate a firmware upgrade. The

host issues a USB reset to the device, and the device then exports a second set of

descriptors in preparation for the Transfer phase. This deactivates the run-time device

drivers associated with the device and allows the DFU driver to reprogram the device’s

firmware unhindered by any other communications traffic targeting the device.

Transfer: The host transfers the firmware image to the device. The parameters

specified in the functional descriptor are used to ensure correct block sizes and timing

for programming the non-volatile memories. Status requests are employed to maintain

synchronization between the host and the device.

Manifestation: Once the device reports to the host that it has completed the

reprogramming operations, the host issues a USB reset to the device. The device re-

enumerates and executes the upgraded firmware.

To ensure that only the DFU driver is loaded, it is considered necessary to change the id-

Product field of the device when it enumerates the DFU descriptor set. This ensures that the

DFU driver will be loaded in cases where the operating system simply matches the vendor

ID and product ID to a specific driver.

4.2.3

Requests

A number of DFU class-specific requests are needed to accomplish the upgrade operations.

Table 5 summarizes the DFU class-specific requests.

For additional information about these requests, please refer to the DFU Class specification.

Table 5.

Summary of DFU class-specific requests

bmRequest

bRequest

wValue

wIndex

wLength

Data

00100001b

DFU_DETACH (0)

wTimeout

Interface

Zero

None

00100001b

DFU_DNLOAD (1)

wBlockNum

Interface

Length

Firmware

10100001b

DFU_UPLOAD (2)

wBlockNum

Interface

Length

Firmware

10100001b

DFU_GETSTATUS(3)

Zero

Interface

Status

00100001b

DFU_CLRSTATUS (4)

Zero

Interface

Zero

None

10100001b

DFU_GETSTATE (5)

Zero

Interface

State

00100001b

DFU_ABORT (6)

Zero

Interface

Zero

None

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