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Publisher24.3 Configuring USB
When
you are installing new USB devices or troubleshooting existing USB
devices, you may need to determine detailed configuration information
about your USB interfaces, drivers, hubs, and ports, including the
following:
It's frequently necessary to know which USB HCI your
system uses. For example, the system requirements for a USB
peripheral may state that it is incompatible with certain USB HCIs.
Also, if you have occasion to troubleshoot a USB problem, knowing
which USB HCI your system uses may allow you to pinpoint the problem
more quickly because various USB HCIs have known limitations and
incompatibilities.
Although Windows generally installs a suitable USB driver, there are
times when upgrading (or downgrading) the default driver is required
to allow USB devices to function properly.
A USB port provides 500 milliamps of current, which is shared by all
devices connected to that port. Connecting several unpowered devices
to a port can exceed the maximum allowable current, which may cause
problems ranging from sporadic operation to complete failure of all
connected devices. Windows allows you to view the total power
consumption for each USB port as well as the power consumed by each
device connected to that port.
The following sections detail the steps necessary to view and change
USB configuration.
24.3.1 Identifying the USB HCI Under Windows 9X
To determine which USB
HCI your system uses under Windows 9X, right-click My Computer,
choose Properties, and click the Device Manager tab to display the
Device Manager, shown in Figure 24-4. Double-click
the Universal Serial Bus controllers item to expand it.
Figure 24-4. Windows 9X Device Manager showing this system uses an Intel 82801AA
24.3.2 Viewing USB HCI Properties Under Windows 9X
From the
Device Manager, double-clicking the Host Controller Interface item
displays the Properties dialog for the HCI, shown in Figure 24-5. This dialog includes detailed HCI information
that may be useful in troubleshooting USB problems and resolving
conflicts.
Figure 24-5. The Windows 9X HCI Properties dialog displaying detailed HCI information
The HCI Properties dialog includes the following pages:
The General page displays summary information about the HCI type,
manufacturer, and version. It also includes the Device status pane,
which indicates when the HCI is working properly and may indicate the
cause when the HCI is not working properly. You can also use the
General page to disable the device in one or more hardware profiles.
The Advanced page includes the Disable USB error detection checkbox,
which sounds like a dangerous thing to do. In fact, disabling USB
error detection is sometimes necessary if USB is to run properly. If
you are not experiencing USB conflicts or problems, leave USB error
detection enabled. Otherwise, try disabling it. This page also
includes the Bandwidth Usage button. Clicking that button displays
the percentage of the available bandwidth consumed by each device
connected to the port. This can be useful information when you
troubleshoot USB problems because some USB devices, particularly
early models, are "bandwidth hogs"
that claim bandwidth regardless of whether they are using it and
thereby prevent other devices connected to the same port from
functioning correctly, if at all.
The Driver page displays the HCI driver provider and version in use
by the HCI. Click the Driver File Details button to display the paths
and filenames of the USB driver files. Click the Update Driver button
to invoke the Update Device Driver Wizard, which allows you to
replace the current driver with a different version. Although the
default driver generally works properly, depending on the HCI your
system uses and the particular devices you have connected, you may
need to replace the driver with a later (or earlier) version for full
functionality.
The Resources page displays the IRQ and I/O port being used by the
HCI. By default, the Use automatic settings checkbox is marked, which
is the proper setting for routine operation. But, depending on the
HCI your system uses and the particular devices you have connected,
you may need to clear that checkbox and assign settings manually. For
example, Windows 9X typically assigns a shared interrupt to the HCI.
Although this usually works properly, some HCIs and some hardware
configurations do not work properly using a shared interrupt. If that
occurs, use the Device Manager to locate an unused interrupt, clear
the Use automatic settings checkbox, and assign the unused interrupt
to the HCI.
24.3.3 Viewing USB Root Hub Properties Under Windows 9X
From
the Device Manager, double-clicking the USB Root Hub item displays
the Properties dialog for the root hub, shown in Figure 24-6. This dialog includes detailed root hub
information that may be useful in troubleshooting USB problems and
resolving conflicts.
Figure 24-6. The Windows 9X Root Hub Properties dialog displaying detailed root hub information
The USB Root Hub Properties dialog includes the following pages:
The General page displays summary information about the root hub
type, manufacturer, and version. It also includes the Device status
pane, which indicates when the root hub is working properly and may
indicate the cause when the root hub is not working properly. You can
also use the General page to disable the device in one or more
hardware profiles.
The Power page includes only the Power properties button. Clicking
this button displays the Power dialog, shown in Figure 24-7. The Hub Information pane of this dialog lists
the hub type and the maximum total power available per port. The
Devices on this Hub pane lists the name and description of each
device connected to the hub and the power it requires. Connecting
multiple unpowered USB devices to a hub is one of the most common
causes of USB problems. If you experience USB problems, use this
dialog to verify that the total power consumption of all connected
devices does not exceed the maximum the port can deliver. Note that
powered USB devices (those that connect to AC power directly) show
very low power consumption, often only 0 mA to 5 mA. That is because
this dialog shows only the power being drawn from the root hub, and
not the power being supplied to the device by a wall outlet.
Figure 24-7. The Windows 9X Power dialog showing all devices connected to the hub and the amount of hub power required by each
The Driver page displays the root hub driver provider and version in
use by the root hub. Click the Driver File Details button to display
the paths and filenames of the USB driver files. Click the Update
Driver button to invoke the Update Device Driver Wizard, which allows
you to replace the current driver with an updated version. Unlike the
HCI driver, you will seldom have occasion to replace the root hub
driver file.
24.3.4 Verifying USB Interrupt Sharing Under Windows 9X
Windows
ordinarily assigns a shared interrupt to the USB HCI, which sometimes
works properly. Often, however, USB works improperly unless the HCI
has a dedicated interrupt. To verify USB interrupt sharing status
under Windows 9X, from the main Device Manager dialog, click the
Properties button to display the Computer Properties dialog shown in
Figure 24-8.
Figure 24-8. Windows 9X Device Manager showing this system shares an interrupt between the USB HCI and an Ethernet adapter
In this instance, the Device Manager shows that USB HCI is sharing
interrupt 09. You can safely disregard the ACPI IRQ Holder for PCI
IRQ Steering entry; IRQ Steering entries are simply placeholders, and
are unlikely to cause conflicts (at least on motherboards that have
ACPI properly implemented, which essentially includes only recent
motherboards that use recent Intel chipsets). Similarly, the SCI IRQ
used by ACPI bus is a system-level entry, which is unlikely to cause
a problem. The Intel 8255x-based PCI Ethernet Adapter (10/100) entry,
however, represents a real piece of hardware that is using real
interrupts and therefore has the potential to cause a conflict. In
this case, it does not. If it did, we would go to the Resources page
of USB HCI Properties and manually assign a dedicated IRQ to it.
24.3.5 Identifying the USB HCI Under Windows 2000/XP
To
determine which USB HCI your system uses under Windows 2000 or
Windows XP, right-click My Computer, choose Properties, display the
Hardware page, and then click the Device Manager button to display
the Device Manager. Double-click the Universal Serial Bus controllers
item to expand it, as shown in Figure 24-9.
Figure 24-9. Windows XP Device Manager showing that this system uses two Intel 82801BA/BAM UHCIs
In this case, as is common on recent systems, the motherboard
includes two distinct HCIs. These operate completely independently,
and each HCI has a separate root hub associated with it. This doubles
the number of root hub ports available, some of which may appear at
the front of the case and some of which connect directly to the
traditional location on the rear ATX I/O panel. Note that the
secondary root hub ports often appear as a set of header pins on the
motherboard, which may be extended to the front or the rear of the
case, as necessary.
24.3.6 Viewing USB HCI Properties Under Windows 2000/XP
From the Device Manager,
double-clicking the Host Controller Interface item displays the
Properties dialog for the HCI, shown in Figure 24-10.
This dialog includes detailed HCI information that may be useful in
troubleshooting USB problems and resolving conflicts.
Figure 24-10. The Windows XP HCI Properties dialog displaying detailed HCI information
The HCI Properties dialog includes the following pages:
The General page displays summary information about the HCI name,
type, manufacturer, and location on the bus. It also includes the
Device status pane, which indicates when the HCI is working properly
and may indicate the cause when the HCI is not working properly. The
Device usage drop-down list allows you to enable or disable the
device. The Troubleshoot button (Troubleshooter in Windows 2000)
invokes an automated dialog that attempts to resolve USB connectivity
problems, although we must say that we seldom find the suggestions it
offers very useful in solving an actual USB problem.
The Advanced page includes the Don't tell me about
USB errors checkbox (Disable USB error detection in Windows 2000).
Although error-detection sounds like a good thing, there are times
when it must be disabled for USB to operate properly. During routine
USB operation, leave USB error detection enabled unless you
experience problems or conflicts. If that happens, try disabling
error detection by marking this checkbox. This page also includes the
Bandwidth-consuming device pane, which displays the percentage of the
available bandwidth consumed by each device connected to the port.
This can be useful information when you troubleshoot USB problems
because some USB devices, particularly early models, are
"bandwidth hogs" that claim
bandwidth regardless of whether they are using it and thereby prevent
other devices connected to the same port from functioning correctly,
if at all.
The Driver page displays the HCI driver provider, date, and version
in use by the HCI, as well as the name of the entity that digitally
signed the driver. Click the Driver Details button to display the
paths and filenames of the USB driver files. Click the Update Driver
button to invoke the Hardware Update Wizard (Upgrade Device Driver
Wizard in Windows 2000), which allows you to replace the current
driver with a different version. Although the default driver
generally works properly, depending on the HCI your system uses and
the particular devices you have connected, you may need to replace
the driver with a later (or earlier) version for full functionality.
Windows XP includes a fourth button, Roll Back Driver, which allows
you to easily revert to the previous driver version if the updated
driver does not function properly.
The Resources page displays the IRQ and I/O port being used by the
HCI. By default, the Use automatic settings checkbox is marked, which
is the proper setting for routine operation. But, depending on the
HCI your system uses and the particular devices you have connected,
you may need to clear that checkbox and assign settings manually, if
that option is available.
24.3.7 Viewing USB Root Hub Properties Under Windows 2000/XP
From the Device Manager,
double-clicking the USB Root Hub item displays the USB Root Hub
Properties dialog, shown in Figure 24-11. This dialog
includes detailed root hub information that may be useful in
troubleshooting USB problems and resolving conflicts.
Figure 24-11. The Windows XP Root Hub Properties dialog displaying detailed root hub information
The USB Root Hub Properties dialog includes the following pages:
The General page displays summary information about the root hub
type, manufacturer, and location. It also includes the Device status
pane, which indicates when the root hub is working properly and may
indicate the cause when the root hub is not working properly. The
Device usage drop-down list allows you to enable or disable the
device. The Troubleshoot button (Troubleshooter in Windows 2000)
invokes an automated dialog that attempts to resolve USB connectivity
problems. The Windows 2000 version is rudimentary, but may be helpful
in resolving simple problems. The Windows XP version is more
polished, but is little more substantive than the Windows 2000
version.
The Power page Hub Information pane lists the hub type and maximum
total power available per port. The Attached Devices pane (Devices on
this hub in Windows 2000) lists the name and description of each
device connected to the hub and the power it requires. If you have
USB problems, use this dialog to verify that the total power
consumption of all connected devices does not exceed the maximum the
port can deliver.
The Driver page displays the root hub driver provider, date, and
version in use by the root hub, as well as the name of the entity
that digitally signed the driver. Click the Driver Details button to
display the paths and filenames of the USB driver files. Click the
Update Driver button to invoke the Hardware Update Wizard (Upgrade
Device Driver Wizard in Windows 2000), which allows you to replace
the current driver with a different version. Windows XP includes a
fourth button, Roll Back Driver, which allows you to easily revert to
the previous driver version if the updated driver does not function
properly. Unlike the HCI driver, you will seldom need to replace the
root hub driver file.
This page, not present in Windows 2000, contains only two checkboxes:
Marking this checkbox, which is enabled by default, allows ACPI to
power down the root hub port after a period of inactivity. We
recommend disabling this option on desktop systems because USB
peripherals frequently do not recover properly when coming out of
standby mode. Problems range from connected peripherals no longer
being recognized to two instances of the same peripheral appearing in
the Device Manager to the peripheral appearing to be recognized
properly but simply not working.
If you have one or more USB devices attached to the root hub that are
capable of waking the system from standby, enabling this checkbox
allows them to do so. For example, you might use a USB modem to
receive incoming faxes. You may want your system available to receive
faxes 24 hours a day but prefer that it not run constantly. If so,
use the Screen Saver tab in Display Properties (or Control Panel
Power Options) to enable power management,shutting down power to the monitor and hard drive after a specified
interval of inactivity, and enable this checkbox. When an inbound fax
call arrives, your USB modem will wake the system and allow it to
receive the fax. Note, however, that PCs do not awake
instantaneously, and the time delay between the wake-up event and
when the system actually becomes available may cause
problems.
24.3.8 Verifying USB Interrupt Sharing Under Windows 2000/XP
To
verify USB interrupt sharing status under Windows 2000 or Windows XP,
from the Device Manager, choose View
Resources byType, and expand the Interrupt request (IRQ) item, as shown in Figure 24-12.
Figure 24-12. Windows XP Device Manager showing that this system dedicates PCI interrupts 19 and 23 to the two USB HCIs
On recent motherboards, Windows 2000 and Windows XP typically assign
a dedicated PCI interrupt above 15 to each device. On older
motherboards, Windows 2000 and Windows XP typically assign a shared
PCI interrupt to the HCI, as shown in Figure 24-13.
Despite all assurances by hardware manufacturers and Microsoft that
USB operates properly with a shared interrupt, that is frequently not
true. If Windows has assigned a shared interrupt to USB, use the
Device Manager to locate an unused interrupt, clear the Use Automatic
Settings checkbox, and assign the unused
interrupt to the HCI.
Figure 24-13. Windows 2000 Device Manager showing that this system shares one interrupt among the USB HCI and four other devices
On the system shown in Figure 24-13, Windows 2000 has
assigned one shared PCI interrupt among the USB HCI, the SCSI host
adapter, the video card, the network adapter,
and the sound adapter. Surprisingly enough, all
of these functions work properly. If a conflict did occur, we would
use the Resources page of USB HCI Properties to manually assign a
dedicated IRQ to it.
24.3.8.1 Configuring USB under Linux
The first draft of this section
originally began, "USB under Linux is not ready for
prime time." We eventually came to realize that USB
under Linux "just works," and the
reason for that change of heart is instructive.In preparing to write this section, we installed current releases of
Red Hat and Mandrake Linux on three representative test-bed
systemsa Pentium III on an i815 motherboard, a Pentium 4 on an
i845PE motherboard, and an Athlon on an n Force2
motherboard. We then connected diverse USB peripherals, from mice and
keyboards to printers and scanners to external optical drives. Some
of them weren't even recognized. Some of them
worked, more or less. Some of them worked sometimes and not other
times. Others didn't work at all. None of them
worked reliably.We had just about written off Linux as having poor USB support.
Fortunately, we have a "back
channel" mailing list of experienced Linux users to
whom we turn when we have questions about Linux hardware issues. We
told them about our problems with USB under Linux, and received many
responses, all of which basically said, "USB works
fine for me under Linux." Hmmm.After much hair-pulling, we finally determined that the problem was
... a bad cable. Trying to make testing more convenient, we did
something stupid. As often happens, cutting corners to save time
actually ended up costing us time. We swapped systems and peripherals
around during the failed initial testing, but we always used the same
cables. One of the cables came with an HP scanner. It looked like a
good cable, but it turned out to be a snake in the grass. If it had
failed completely, we would have isolated the problem quickly. But it
"almost worked," and that cost us
days of frustration. If we'd followed our own
troubleshooting advice we'd have solved the problem
quickly. The moral is, if you're having USB
problems, try using a known-good cable.
configuration. If you run a recent Linux release on modern hardware,
USB generally just works. The usual caveats apply, however. Recent
Intel HCIs are much less likely to have compatibility problems than
are older HCIs and those from some other manufacturers. VIA HCIs in
particular seem to have as many USB problems under Linux as they do
under Windows. Accordingly, it is important to determine the HCI your
motherboard uses.The KDE Control Center provides an
easy way to identify the HCI. To use it for this purpose, start KDE
Control Center, expand the Information branch in the left pane,
double-click the PCI item, and scroll down in the right pane to
locate the USB HCI items. Figure 24-14 shows dual
82801BA/BAM HCIs on an Intel ICH2 motherboard. The ICH2 HCIs are
well-behaved in general, and function well under Linux. The HCI
listing also provides other useful information, including the I/O
port addresses and interrupts assigned to each HCI.
Figure 24-14. KDE Control Center displaying HCI type, I/O
ports, and interrupts
From the command line,
you can display HCI information using the command
/sbin/lspci -v|grep
HCI, the output from which is shown in the
following example:
00:1f.2 USB Controller: Intel Corp. 82801BA/BAM USB (Hub #1) (rev 05) (prog-if 00 [UHCI])
00:1f.4 USB Controller: Intel Corp. 82801BA/BAM USB (Hub #2) (rev 05) (prog-if 00 [UHCI])
02:00.0 FireWire (IEEE-1394): Lucent Microelectronics FW323 (rev 04) (prog-if 10 [OHCI])
You can also use KDE Control Center to determine interrupt-sharing
status by double-clicking the Interrupts item. Figure 24-15 shows that the first usb-uhci has exclusive
use of Interrupt 10, but that the second usb-uhci shares Interrupt 11
with ohci1394 (a FireWire interface) and eth0 (an Ethernet
interface). Although shared interrupts may cause USB conflicts under
Windows, we have never encountered any problems with a USB shared
interrupt under Linux.
Figure 24-15. KDE Control Center displaying interrupt assignments
KDE Control Center can also list USB devices. To display a list of
connected USB devices, double-click the USB Devices item. To view the
details for a device, double-click that device. For example, Figure 24-16 shows the details for a UMAX Astra 3400U
scanner. (We still haven't figured out what the
"Unknown" device is, but it shows
up regularly and doesn't seem to cause any
problems.)
Figure 24-16. KDE Control Center displaying details for connected USB devices
If you don't have KDE installed or if you simply
prefer the command line, use the command cat
/proc/bus/usb/devices to display more USB configuration
information than you'll know what to do with. The
following example shows the USB configuration for the same system
used for the previous GUI example:
T: Bus=02 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
B: Alloc= 11/900 us ( 1%), #Int= 1, #Iso= 0
D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=0000 ProdID=0000 Rev= 0.00
S: Product=USB UHCI Root Hub
S: SerialNumber=ef80
C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms
T: Bus=02 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
D: Ver= 1.10 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=8086 ProdID=1122 Rev= 0.00
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=255ms
T: Bus=02 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=12 MxCh= 0
D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=1606 ProdID=0060 Rev= 1.00
S: Manufacturer=UMAX
S: Product=USB SCANNER
C:* #Ifs= 1 Cfg#= 1 Atr=00 MxPwr= 0mA
I: If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=ff Driver=(none)
E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=16ms
E: Ad=82(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=03(O) Atr=02(Bulk) MxPS= 64 Ivl=0ms
T: Bus=02 Lev=02 Prnt=02 Port=01 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
P: Vendor=04b8 ProdID=0005 Rev= 1.00
S: Manufacturer=EPSON
S: Product=USB Printer
S: SerialNumber=W30169912131319590
C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr= 2mA
I: If#= 0 Alt= 0 #EPs= 2 Cls=07(print) Sub=01 Prot=02 Driver=usblp
E: Ad=01(O) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=82(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
T: Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
B: Alloc= 0/900 us ( 0%), #Int= 0, #Iso= 0
D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=0000 ProdID=0000 Rev= 0.00
S: Product=USB UHCI Root Hub
S: SerialNumber=ef40
C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms
The default USB configuration is suitable for most purposes. However,
if you need to tweak the USB configuration, you can rebuild the
kernel with different USB support options. The KDE Linux Kernel
Configurator, shown in Figure 24-17, provides an easy
way to do that.
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Figure 24-17. The Linux Kernel Configurator
Reconfiguring
USB support options in the kernel is not for the faint of heart.
Before you attempt it, make sure to read and understand the detailed
technical documentation available on the Linux USB Project web site
(http://www.linux-usb.org/).To run the KDE Linux Kernel Configurator, log on as
root, start KDE Control Center, expand the System item in the left
menu pane, and choose Linux Kernel Configurator. Make any necessary
changes, save those changes, compile and install the new kernel, and
reboot the system. If you don't know how to compile
and install a kernel, see the Linux Kernel HOWTO (http://www.tldp.org/HOWTO/Kernel-HOWTOl).Always save the new kernel under a different name. That
way, if the new kernel won't boot, you can simply
boot to the old kernel. If there's a problem with
the new kernel and you saved it under the same name as the old
kernel, your system may be unbootable.
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