Universal Serial Bus (USB)
is a low-cost, hot-pluggable device bus
that is supported by most modern motherboards and
is also available through add-in cards.
In SCO OpenServer, the USB interface is implemented
via the Uniform Driver Interface (UDI).
Three USB Host Controller Interfaces (HCI) exist
and are supported by this implementation:
Universal Host Controller Interface (UHCI)
Open Host Controller Interface (OHCI)
Enhanced Host Controller Interface (EHCI)
USB 1.1 devices are typically low-cost, low-bandwidth units.
USB 2.0 offers speeds up to 480 megabits per second,
which is comparable to mid-range IDE and SCSI bus speeds.
USB hubs and USB devices
(such as mice, keyboards, and mass storage devices)
may be plugged into the host.
A maximum of 128 devices may be nested up to 8 layers deep
using combinations of hubs and devices.
USB devices may be attached before
or after the host computer starts;
devices may be unplugged from the bus while the computer is running.
Mouse and keyboard devices send very little data
across the USB bus.
Other devices, such as mass storage, use bulk transfer mode
to move data blocks over the bus,
but the data rates achieved are typically less
than SCSI or IDE bus devices.
USB is an effective mechanism for adding devices to a host
that does not already have that functionality,
such as adding a mouse or trackball to a laptop
or adding supplementary storage such as a Zip® or CD-ROM drive.
USB can be used for hard disk storage
when top performance is not required.
Note the following when using these supported USB device types:
Powered hubs are recommended over unpowered hubs.
USB keyboards work like AT and PS/2 keyboards.
The simultaneous use of multiple USB keyboards,
along with one AT or PS/2 keyboard, is supported.
LEDs and shift states are synchronized across
all keyboards physically attached to a system.
If you press the <Caps Lock> key on one keyboard,
the Caps Lock state (including the LEDs)
is active on all keyboards.
If you hot-add a USB keyboard,
it ``adopts'' the current LED and shift state.
USB keyboards cannot be used in the
when the kernel has been shut down.
This means that you are unable to reboot
at the system shutdown prompt
using a USB keyboard:
** Safe to Power Off **
** Press Any Key to Reboot **
using the in-kernel version of the scodb kernel debugger.
``Using SCODB'' in the SCODB User's Guide.)
You can enter the debugger from a USB keyboard
but after that, the keyboard will not function.
Systems that have scodb linked into the
kernel and/or have hotkeys defined for the debugger
should have an AT or PS/2 keyboard.
Alternately, you can configure the debugger to
use a serial console -- see
``Setting up serial consoles'' in the SCO OpenServer Handbook
for more information.
USB mice work like keyboard mice
(also known as PS/2 mice).
Any USB Human Interface Device that is a pointing
device should work with the USB mouse driver.
Scrolling wheels are supported.
Three button mice are supported.
Additional buttons are ignored by the X server.
You can have more than one USB mouse attached
to the system at the same time.
However, all USB mice are channeled
through a single event channel.
It is not possible to separately associate one
USB mouse with one terminal and
another USB mouse with a different terminal.
Having multiple USB mice might be useful
if one of the devices is a joystick, graphics tablet,
touchscreen, or other pointing device.
For multiple mice, the inputs are effectively connected together.
It is possible, for example, to move the pointer with one USB mouse
and click a mouse button on a different mouse;
both operations are accepted as if they came from the same mouse.
If you have identical mice and you move them in
opposite directions at exactly the same speed,
the mouse pointer remains still.
Multiple printers can be used on a system.
Printers can be attached and removed from the
USB bus at any time.
In order for a printer to be supported, there must
be a user-level driver/filter specific to that printer available.
The printer drivers are accessed through device nodes
in /etc/usb (see
for more information).
Printer status can be obtained from
ioctl with the ``u_op'' field set to
These constants and the needed data structures
can be found in the giousr.h file.
Status is returned as one byte and conforms to the
Universal Serial Bus Device Class
Definition for Printing Devices, Version 1.1
CD-ROM/DVD-ROM drives and CD/DVD writers
Multiple CD-ROM and DVD-ROM drives and writers
can be used on a system.
Removing an attached CD-ROM or DVD-ROM drive
(especially one that is mounted) may trigger a problem
elsewhere in the system.
Devices that support software media lock are locked
while they are in use by the operating system.
Devices with mechanical media releases
(for example, a CD-ROM drive with a hinged door instead of a tray)
cannot be locked.
Ejecting the media while the device is in use by the operating system
can cause data corruption or a system panic.
The ``root hub'' refers to the USB ports configured
on the motherboard. Many systems allow built-in USB ports
to be disabled in BIOS setup. If USB is
not working, check that it is enabled in the BIOS.
Alternatively, if you do not wish to use USB,
you may want to disable it in the BIOS setup
since many motherboards use two to three interrupts
for USB HCIs.
The root hub ports may be used for either a USB device
or a USB hub. Any combination of hubs and devices may be
connected, up to the maximum device limit and
the hub depth -- 128 devices nested 8 layers deep.
USB devices are supported by a layered software implementation.
Inside the kernel, there are several layers of software
for USB support,
including the USB protocol stack and USB class drivers.
USB devices are configured using the
commands, such as mkdev mouse or mkdev hd.
These commands provide access to USB devices from user applications.
USB protocol stack
The central driver of the USB protocol stack
is the USB stack manager, usbd.
This driver maintains an internal representation
of the ``tree'' of USB hubs and devices.
It notices the appearance and disappearance of devices
as they are physically attached to and removed from ports and hubs.
usbd attaches and detaches device descriptors
to the corresponding USB class drivers.
USB class drivers
USB class drivers handle
the attaching, detaching, and accessing of various classes of devices.
SCO OpenServer includes separate class drivers for
keyboard and mouse (usb_hid),
mass storage devices (usb_msto),
and hubs (usb_hub).
USB device configuration
USB mass storage devices look
like SCSI devices to the kernel.
The following table lists
the different types of USB storage devices,
the corresponding SCSI driver name,
script you use to configure the device:
Sdsk or Sflp
mkdev hd, mkdev flopti (mkdev ls120)
When you physically attach a USB storage device to the system,
a kernel configuration message is displayed on the console.
As an example, a hard disk might produce a message similar to:
usb_msto (USB Mass Storage)
is the name of the SCSI Host Bus Adapter driver.
The id number is the USB device ID
assigned to the mass storage device.
All storage devices attached to the USB bus
are assigned a USB device ID,
determined by the order in which the device is detected by the system.
``USB device IDs''
for more information.
The unit number refers to unit numbers of the peripheral driver.
In this example, unit=1 indicates that this
is the second SCSI disk in the system.
A value of ``0'' would indicate the first SCSI hard drive.
Once the USB storage device is plugged in,
you must run the appropriate
script, as shown in the above table.
You are prompted for the USB device ID
that was listed in the id= field
in the kernel configuration message.
(You can also determine a device's ID by running
with the -h option and locating the
entry for the desired USB device
in the resulting hardware list.)
Normally when adding a new SCSI device,
you are required to relink the kernel and reboot the system.
Because USB devices are hot-pluggable,
however, this step is not always necessary.
Configuring hard disks
Use mkdev hd to configure USB hard disks,
supplying the appropriate USB device ID for the device.
Using the hard disk example shown above, you would enter USB ID 2.
Because the device is already present and recognized,
it is not necessary to relink the kernel and reboot the system.
You then need to run mkdev hd a second time
to set up partitions, divisions, and filesystems.
Configuring removable storage devices
Removable USB storage devices, such as
Zip, Jaz®, LS-120, LS-240, and floppy drives,
flash memory devices, and certain cameras,
are recognized by both the Sdsk and Sflp drivers.
To configure a removable storage device as a floppy drive,
use mkdev flopti (or mkdev ls120).
Typically, this is how you want to configure removable
storage devices, unless you specifically want to establish
partitions and divisions on the device's ``disk''.
To configure a removable storage device as a hard disk,
with partitions and divisions, use mkdev hd.
You cannot use USB removable storage devices,
including floppy and LS-120/LS-240 drives,
to format media.
By default, the system kernel is configured with the
/dev/fd0 and /dev/fd1 device nodes.
Depending on the number of traditional floppy drives
attached to the motherboard floppy controller,
you may be able to use one or both of these device nodes
for USB removable devices, instead of running
For example, if your system contains one traditional floppy drive,
you can access one USB removable storage device
If you are not using any traditional floppy drives,
you can access two USB removable storage devices
from /dev/fd0 and /dev/fd1.
Sflp units are enumerated last in the list
of floppy devices. If there is a standard floppy drive
and a USB LS-120 drive on the system,
the LS-120 will be /dev/fd1
and the standard floppy drive will be /dev/fd0.
Most of the other floppy device nodes created (see
for details) are only useful for USB removable
storage devices that can use traditional
floppy media (for example, floppy and LS-120 drives).
Also see the
manual page for more information.
Configuring CD-ROM and DVD-ROM drives and writers
Use mkdev cdrom to configure
USB CD-ROM and DVD-ROM devices.
These devices can be mounted
for read-only random access.
Writable devices can be written
with software such as cdrecord.
USB device IDs
When you attach a USB mass storage device,
the system assigns the device a USB device ID.
(USB device IDs are only assigned
to USB storage devices, not to non-storage
devices like mice and keyboards.)
USB device IDs are determined by the order
in which the system detects each device.
However, the enumeration of devices depends
on several factors and different circumstances
may result in different device ID assignments
on the same machine.
For example, devices that you attach to a running system are
enumerated in the order that you plug them in.
At boot time, however, the entire USB hub/device tree
is traversed and devices may be detected in
a different order, resulting in different device ID
assignments. In general, these guidelines apply:
if you attach all of your USB storage devices
while the system is turned off,
the enumeration order when the computer is
started will likely persist between system reboots.
if you hot-add or hot-remove USB storage devices,
device IDs may change when the system is rebooted.
if you add, remove, or change the order of
USB storage devices on a non-running system that
previously contained USB storage devices,
device IDs may be different when the system
The following example illustrates a situation in
which previously assigned USB device IDs
If you have a computer that contains
a USB CD-ROM drive
as the only USB storage device,
the CD-ROM drive
is assigned USB device ID 0
when the system is booted. If you then hot-add
a USB LS-120 drive,
it is assigned USB device ID 1.
Finally, you plug in an external USB hard drive
and it is assigned USB device ID 2.
After running mkdev cdrom, mkdev ls120,
and mkdev hd to configure the USB
storage devices, the appropriate device nodes are
created and the
is updated to contain entries similar to:
In this example, when you reboot the system,
it is possible that the USB LS-120 device
could now be assigned device ID 2 and
the USB hard drive has switched to device ID 1.
(If the CD-ROM drive remains the first
detected device in the USB chain,
it would retain device ID 0.)
Now, if you access /dev/hd10,
the system tries (most likely unsuccessfully)
to use the LS-120 drive instead
of the hard drive, and vice versa.
If you encounter a situation like this,
you need to edit the
file and modify the usb_msto entries
so the correct device IDs are assigned to the
(To confirm the USB device ID
assignments on your system, run hwconfig -h.
Check the value of the id= field for each of the
USB mass storage device entries
(usb_msto) in the list of hardware.
In this example, you would
change the mscsi file to read:
After editing the mscsi file,
you need to relink the kernel and reboot the system.
When the system is running again,
the attached USB storage devices should now function properly.
Any time you make a change to the number or order
of USB storage devices on the system,
you may need to edit the mscsi file as described above.
manual pages for more information.
Device drivers in the USB protocol stack
Controls I/O to the various USB host controllers
found on motherboards and add-in cards.
The HCI drivers include:
Communications interface between the USB stack
and the HCI drivers.
USB stack manager
Communications interface between the USB stack
and the HCI drivers.
This driver maintains an internal representation
of the ``tree'' of USB hubs and devices,
and attaches/detaches device descriptors to corresponding
USB class drivers as USB
peripherals are added/removed.
USB stack utilities library
Utility functions used by usbd.
OpenUSBDI UDI meta-language
USB ``tree'' management functions used by usbd.
Hub (USB class driver)
Class driver for managing USB hubs.
Printer (USB class driver)
Class driver for managing USB printers.
Mass storage (USB class driver)
The pseudo Host Bust Adapter driver. This is the driver that
appears in the
file to attach USB storage devices to
SCSI peripheral drivers.
Human Interface Device (USB class driver)
Class driver for talking to Human Interface Devices
(mice, keyboards, and so forth.)
Human Interface Device parser library
Functions for decoding messages from HID devices.
Human Interface Device UDI meta-language
Functions for controlling HID devices.
SCO OpenServer keyboard mapper
Connects HID keyboard type devices
to the SCO OpenServer console driver.
SCO OpenServer mouse mapper
Connects HID ``pointing device'' type devices
to the SCO OpenServer event driver.