USB support
===========

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 :ref:`command_usb` or :ref:`command_detect` command.
USB devices in barebox are not hot-pluggable. It is expected that USB
devices are not disconnected while barebox is running.

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 :ref:`command_ifup` command, add the
following to ``/env/network/eth0-discover``:

.. code-block:: sh

  #!/bin/sh

  usb

USB mass storage
^^^^^^^^^^^^^^^^

barebox supports USB mass storage devices. After probing them with the :ref:`command_usb`
command, they show up as ``/dev/diskx`` and can be used like any other device.

USB device support
------------------

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 :ref:`command_dfu` 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
:ref:`command_dfu`. A typical ``dfu`` command could look like this:

.. code-block:: sh

  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 <http://dfu-util.gnumonks.org/>`_ 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:

.. code-block:: sh

  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.