USB DFU - The USB Device Firmware Upgrade standard
USB Device Firmware Upgrade (DFU) is an official USB device class specification of the USB Implementers Forum.
It specifies a vendor and device independent way of updating the firmware of a USB device. The idea is to have only one vendor-independent firmware update tool as part of the operating system, which can then (given a particular firmware image) be downloaded into the device.
In addition to firmware download, it also specifies firmware upload, i.e. loading the currently installed device firmware to the USB Host.
The current version is 1.1, it can be found for free download at http://www.usb.org/developers/devclass_docs/DFU_1.1.pdf
Despite its clear architecture and DFU being an official USB standard, very few companies are known to have implemented it in their products. In the Free Software / Hardware area, most notably the [OpenPCD] project has used it for their Free RFID readers.
OpenMoko and USB DFU
Since OpenMoko is a big supporter of open standards and protocols, it has chosen USB DFU as the way to do "firmware" (actually, general software) updates on its official devices.
USB DFU on the Neo1973
The DFU implementation is part of our version of the u-boot bootloader.
You can use it with any USB DFU 1.1 compliant utility. We also have developed our own dfu-util program.
Type of DFU Download
The Neo1973 has enough SDRAM to accomodate a download mechanism according to Chapter 6.1 Mechanism "1." (to receive the entire image into a buffer and perform the actual programming during the manifestation phase). We are using this mechanism for the u-boot partition to prevent users from "bricking" their device if something goes wrong during the transfer.
For other partitions (kernel, rootfs, ...) however, future devices will have more NAND than SDRAM. Thus, we implement a download mechanism according Chapter 6.1 Mechanism "2." for all non-bootloader partitions.
USB DFU Interfaces
The Neo1973 has the following USB Alternate Interfaces for DFU:
- RAM. This downloads executable code into RAM (address 0x32000000) and executes it
- the u-boot bootloader partition in NAND flash
- the u-boot environment partition in NAND flash
- the kernel partition in NAND flash
- the splash partition in NAND flash
- the rootfs partition in NAND flash.