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DEVICE FIRMWARE UPGRADE (DFU) IMPLEMENTATION IN ST7 USB DEVICES

When a USB reset signal is received, the USB reset interrupt routine checks this variable. If a

DETACH has previously been received, the device exports the DFU Mode descriptor set, oth-

erwise it exports its normal run-time descriptor set.

2.6 TRANSFER PHASE

The Transfer phase begins after the device has processed the USB reset and exported the

DFU Mode descriptor set. Both downloads and uploads of firmware can take place during this

phase. This transfer phase consists of a succession of DFU requests according to the state di-

agram defined in the DFU Class specification (Fig A1 page 26).

2.6.1 Downloading

The host slices the firmware image file into N pieces and sends them to the device by means

of control-write operations in the default endpoint (Endpoint 0).

The maximum number of bytes that the device can accept per control-write transaction is

specified in the

wTransferSize field of the DFU Functional Descriptor.

There are several possible download mechanisms . The third mechanism described in

chapter 6.1 of the

USB Device Firmware Upgrade Specification is implemented in this project:

1. A large portion of memory is erased. In our case all of Sector 1 and/or all of Sector 2.

2. Small firmware blocks are written. 8 bytes in the LS project, 128 bytes in the FS project.

Note: The number of bytes sent to the device in a control-write transfer is indicated by the

wTransferSize field of the DFU Functional Descriptor.

2.6.2 Uploading

The purpose of an Upload is to retrieve and archive a device’s firmware. It is by definition the

reverse of a Download. After Upload the Host should have a DFU suffix in the file where the

data are saved. This suffix contains useful information like the VendorID, ProductID, Firmware

Version, etc...

2.7 MANIFESTATION PHASE

After the transfer phase is terminated, the device is ready to execute the new firmware. To do

this the host must send a USB reset to re-enumerate the device in normal run-time operation.