USBD(4) USBD(4)
NAME
usbd - Universal Serial Bus daemon
SYNOPSIS
usbd [ -Dd ] [ -s srv ] [ -m mnt ] [ hub... ]
DESCRIPTION
Usbd complements usb(3) to provide USB I/O for device
drivers. It enumerates the bus, polling hub ports to detect
device attachments and detachments, performs initial config-
uration of setup endpoints, and writes extra information
into usb(3) endpoint control files, to ease device location.
By default, usbd opens all setup endpoints found at #u/usb
(which correspond to built-in hubs initialized by the kernel
during boot). Paths to directories representing setup end-
points for hubs can be given as arguments to restrict usbd
operation to such hubs.
When a device is attached, depending upon a configuration
file compiled into usbd , the appropriate device driver may
be started without user intervention. This mechanism can be
used to statically link some USB device drivers into usbd
itself. Initial configuration for setup endpoints is per-
formed independently of this configuration.
Usbd provides a file interface used to change debugging
flags, and also used by USB device drivers statically linked
into usbd. By default, the file system is mounted (after) at
/dev and a 9P connection is posted at /srv/usb.
Besides files provided by device drivers, the file usbdctl
is always present in the file interface. It accepts these
control requests:
debug n Sets the debugging level to n.
fsdebug n Sets the file system debugging level to n.
dump Prints the list of devices and file systems known
by usbd.
Usbd recognizes the following options:
-d Print debugging diagnostics. Repeating the option
increases verbosity.
-D Print debugging diagnostics for the file system
interface.
-m mnt Mount the served file system at mnt.
-s srv Post a 9P connection at #s/srv.
Configuration
Page 1 Plan 9 (printed 12/21/24)
USBD(4) USBD(4)
Usbd can be configured to start drivers for devices matching
one or more CSPs (hex representation of USB class, subclass
and protocol), class, subclass, protocol, vendor id, or
device id. When a new device is attached, usbd scans the
configuration and, if an entry matches the device descrip-
tor, starts the driver. If no driver is configured, the
setup endpoint for the device is left configured to let the
user start the driver by hand.
Configuration is via compilation because one of the options
is to embed (link) the driver into the usbd binary. If the
driver is embedded, usbd creates a process for it and calls
its main entry point. Otherwise, usbd tries to locate the
driver binary in /bin/usb and creates a process to execute
it.
The configuration file, usbdb, has two sections: embed and
auto. Each section includes lines to configure particular
drivers. A driver may have more than one line if necessary.
Each line includes the name of the driver (the base name of
the binary) and one or more attributes of the form
name=value
The following attributes exist:
class Value may be the name of the class or a number
identifying the device class (using C syntax).
The following class names are known: audio, comms,
hid, printer, storage, hub, and data.
subclass Value is the number of the device subclass.
proto Value is the number of the device protocol.
csp Value is the hexadecimal number describing the CSP
for the device.
vid Value is the vendor id.
did Value is the device id.
args This must be the last field. The value is the
rest of the line, and is supplied as arguments to
the driver process.
Several environment variables can be used to alter the
behaviour of usbd, for example, for use in plan9.ini(8).
usbdebug sets a debug level (zero for no diagnostics and
positive values for increasing verbosity). kbargs overrides
the keyboard arguments as specified by the configuration
file. diskargs overrides the disk arguments in the same
way.
EXAMPLE
This configuration file links usb/kb into usbd when it is
compiled. It arranges for the driver's entry point, kbmain
in this case, to be called for any device with CSPs matching
Page 2 Plan 9 (printed 12/21/24)
USBD(4) USBD(4)
either 0x010103 or 0x020103. Option -d will be supplied as
command line arguments for kbmain. This configuration also
arranges for /bin/usb/disk to start (with no arguments)
whenever a device of class storage is attached.
embed
kb csp=0x010103 csp=0x020103 args=-d
auto
disk class=storage args=
FILES
/srv/usb 9P connection to the driver file system.
/dev mount point for the driver file system.
/sys/src/cmd/usb/usbd/usbdb
Configuration file deciding which devices are
included into usbd and which ones are started
automatically.
SOURCE
/sys/src/cmd/usb/usbd
SEE ALSO
usb(2), usb(3), usb(4)
BUGS
Usbd is not supposed to be restarted. This is arguable.
Not heavily exercised yet.
Page 3 Plan 9 (printed 12/21/24)