1.16. USB support¶
1.16.1. 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.
126.96.36.199. 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
1.16.2. USB device support¶
barebox supports several different USB gadget drivers:
Device Firmware Upgrade (DFU)
The recommended way to use USB gadget is with the usbgadget - Create USB Gadget multifunction device command. While there are individual commands for dfu - device firmware update and usbserial - serial gadget enable/disable, the usbgadget - Create USB Gadget multifunction device commands supports registering composite gadgets.
188.8.131.52. Partition description¶
The USB gadget commands for Android Fastboot and DFU take a partition description
which describes which barebox partitions are exported via USB. The partition
description is referred to as
<desc> in the command help texts. It has
the general form
The partition field is the partition as accessible in barebox. This can be a
/dev/, but could also be a regular file.
The name field is the name under which the partition shall be exported. This is the name under which the partition can be found with the host tool.
Several flags are supported, each denoted by a single character:
sSafe mode. The file is downloaded completely before it is written (DFU specific)
rReadback. The partition is allowed to be read back (DFU specific)
cThe file shall be created if it doesn’t exist. Needed when a regular file is exported.
uThe partition is a MTD device and shall be flashed with a UBI image.
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 usbgadget - Create USB Gadget multifunction device or the dfu - device firmware update command.
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
dfu-util command automatically finds DFU-capable devices. If there are
multiple devices found, you need to identify one with the
184.108.40.206. USB serial console¶
barebox can provide a serial console over USB. This can be initialized with the
usbserial - serial gadget enable/disable command. Once the host is plugged in it should show a
new serial device, on Linux for example
220.127.116.11. Android Fastboot support¶
barebox has support for the android fastboot protocol. There is no dedicated command for initializing the fastboot protocol, instead it is integrated into the Multifunction Composite Gadget, see usbgadget - Create USB Gadget multifunction device for a usage description.
The Fastboot gadget supports the following commands:
fastboot flash additionally supports image types UBI and Barebox. For UBI
Images and a MTD device as target, ubiformat is called. For a Barebox image
with an available barebox update handler for the fastboot exported device, the
barebox_update is called.
The barebox Fastboot gadget supports the following non standard extensions:
fastboot getvar allShows a list of all variables
fastboot oem getenv <varname>Shows a barebox environment variable
fastboot oem setenv <varname>=<value>Sets a barebox environment variable
fastboot oem exec <cmd>executes a shell command. Note the output can’t be seen on the host, but the fastboot command returns successfully when the barebox command was successful and it fails when the barebox command fails.
Example booting kernel/devicetree/initrd with fastboot
In Barebox start the fastboot gadget:
usbgadget -A /kernel(kernel)c,/initrd(initrd)c,/devicetree(devicetree)c
On the host you can use this script to start a kernel with kernel, devicetree and initrd:
#!/usr/bin/env bash set -e set -v if [ "$#" -lt 3 ] then echo "USAGE: $0 <KERNEL> <DT> <INITRD> [<ARGS>]" exit 0 fi kernel=$1 dt=$2 initrd=$3 shift 3 fastboot -i 7531 flash kernel $kernel fastboot -i 7531 flash devicetree $dt fastboot -i 7531 flash initrd $initrd fastboot -i 7531 oem exec 'global linux.bootargs.fa'$ct'=rdinit=/sbin/init' if [ $# -gt 0 ] then ct=1 for i in $* do fastboot -i 7531 oem exec 'global linux.bootargs.fa'$ct'='"\"$i\"" ct=$(($ct + 1)) done fi timeout -k 5 3 fastboot -i 7531 oem exec -- bootm -o /devicetree -r /initrd /kernel
18.104.22.168. USB Composite Multifunction Gadget¶
With the Composite Multifunction Gadget it is possible to create a USB device with multiple functions. A useful combination is creating a Fastboot gadget and a USB serial console. This combination can be created with:
usbgadget -A /dev/mmc2.0(root),/dev/mmc2.1(data) -a
-A option will create a Fastboot function providing
/dev/mmc2.0 as root
/dev/mmc2.1 as data partition. The
-a option will create a
USB CDC ACM compliant serial device.
Unlike the dfu - device firmware update command the
usbgadget command returns immediately
after creating the gadget. The gadget can be removed with
1.16.3. USB OTG support¶
barebox does not have USB OTG support. However, barebox supports some USB cores in
both host and device mode. If these are specified for otg in the device tree
(dr_mode = “otg”;) barebox registers a OTG device which can be used to decide which
mode shall be used. The device has a
mode parameter which by default has the
otg. setting this to
peripheral puts the device in the corresponding
mode. Once a specific mode has been selected it can’t be changed later anymore.
barebox:/ devinfo otg0 Parameters: mode: otg ("otg", "host", "peripheral") barebox:/ otg0.mode=host musb-hdrc: ConfigData=0xde (UTMI-8, dyn FIFOs, bulk combine, bulk split, HB-ISO Rx, HB-ISO Tx, SoftConn) musb-hdrc: MHDRC RTL version 2.0 musb-hdrc: setup fifo_mode 4 musb-hdrc: 28/31 max ep, 16384/16384 memory barebox:/
1.16.4. USB Gadget autostart Support¶
Barebox can be configured to start usbgadget automatically by using global variables, instead of creating boot script. This can be useful if autostart policy should be chosen at boot time from other driver or script. To get usbgadget autostart support barebox has to be compiled with CONFIG_USB_GADGET_AUTOSTART enabled.
22.214.171.124. USB Gadget autostart Options¶
Boolean flag. If set to 1, usbgadget will be started automatically on boot and enable USB OTG mode. (Default 0).
Boolean flag. If set to 1, CDC ACM function will be created. See usbgadget - Create USB Gadget multifunction device -a. (Default 0).
Common function description for all of DFU, fastboot and USB mass storage gadgets. Both Fastboot and DFU partitions also have dedicated override variables for backwards-compatibility:
Function description for DFU. See usbgadget - Create USB Gadget multifunction device -D [desc].
Function description for fastboot. See usbgadget - Create USB Gadget multifunction device -A [desc].
Export barebox update handlers. See usbgadget - Create USB Gadget multifunction device -b. (Default 0).