15. USB support

15.1. USB host support

barebox has support for both USB host and USB device mode. USB devices take a long time to probe, so they are not probed automatically. Probing has to be triggered using the usb ((re-)detect USB devices) or detect - detect devices command. USB devices in barebox are not hot-pluggable. It is expected that USB devices are not disconnected while barebox is running.

15.1.1. USB Networking

barebox supports ASIX-compatible devices and the SMSC95xx. After detection, the device shows up as eth0 and can be used like a regular network device.

To use a USB network device together with the ifup - bring a network interface up command, add the following to /env/network/eth0-discover:

#!/bin/sh

usb

15.1.2. USB mass storage

barebox supports USB mass storage devices. After probing them with the usb ((re-)detect USB devices) command, they show up as /dev/diskx and can be used like any other device.

15.2. USB device support

15.2.1. DFU

USB Device Firmware Upgrade (DFU) is an official USB device class specification of the USB Implementers Forum. It provides a vendor-independent way to update the firmware of embedded devices. The current specification is version 1.1 and can be downloaded here: http://www.usb.org/developers/devclass_docs/DFU_1.1.pdf

On the barebox side, the update is handled with the dfu - device firmware update command. It is passed a list of partitions to provide to the host. The partition list has the form <file>(<name>)<flags>. file is the path to the device or regular file which shall be updated. name is the name under which the partition shall be provided to the host. For the possible flags see dfu - device firmware update. A typical dfu command could look like this:

dfu "/dev/nand0.barebox.bb(barebox)sr,/dev/nand0.kernel.bb(kernel)r,/dev/nand0.root.bb(root)r"

On the host side, the tool dfu-util can be used to update the partitions. It is available for most distributions and typically supports the following options:

dfu-util -h
Usage: dfu-util [options] ...
  -h --help                     Print this help message
  -V --version                  Print the version number
  -v --verbose                  Print verbose debug statements
  -l --list                     List the currently attached DFU capable USB devices
  -e --detach                   Detach the currently attached DFU capable USB devices
  -d --device vendor:product    Specify Vendor/Product ID of DFU device
  -p --path bus-port. ... .port Specify path to DFU device
  -c --cfg config_nr            Specify the Configuration of DFU device
  -i --intf intf_nr             Specify the DFU Interface number
  -a --alt alt                  Specify the Altsetting of the DFU Interface
                                by name or by number
  -t --transfer-size            Specify the number of bytes per USB Transfer
  -U --upload file              Read firmware from device into <file>
  -D --download file            Write firmware from <file> into device
  -R --reset                    Issue USB Reset signalling once we're finished
  -s --dfuse-address address    ST DfuSe mode, specify target address for
                                raw file download or upload. Not applicable for
                                DfuSe file (.dfu) downloads

To update the kernel for the above example, you would use something like the following:

dfu-util -D arch/arm/boot/zImage -a kernel

The dfu-util command automatically finds DFU-capable devices. If there are multiple devices found, you need to identify one with the -d/-p options.