24.3 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:
- USB Host Controller Interface
-
It's frequently necessary to know which USB Host
Controller Interface 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.
- USB driver information
-
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.
- USB power information
-
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 Device
Manager, shown in Figure 24-4. Double-click the
Universal Serial Bus controllers item to expand
it.
24.3.2 Viewing USB HCI Properties Under Windows 9X
From 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.
The HCI Properties dialog includes the following pages:
- General page
-
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.
- Advanced page
-
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 BandwidthUsage
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 whether they are using it or not and thereby prevent other
devices connected to the same port from functioning correctly, if at
all.
- Driver page
-
The Driver page displays the HCI driver provider and version in use
by the HCI. Click the DriverFileDetails button to display the paths and filenames of the
USB driver files. Click the UpdateDriver 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.
- Resources page
-
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
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 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.
The USB Root Hub Properties dialog includes the following pages:
- General page
-
The General page displays summary information about the root hub
type, manufacturer, and version. It also includes the
DeviceStatus 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.
- Power page
-
The Power page includes only the PowerProperties button. Clicking this button displays the Power
dialog, shown in Figure 24-7. The HubInformation 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.
- Driver page
-
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.
In this instance, 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 Device Manager.
Double-click the Universal Serial Bus
controllers item to expand it, as shown in Figure 24-9.
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 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.
The HCI Properties dialog includes the following pages:
- General page
-
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.
- Advanced page
-
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 whether they are using it or not and thereby prevent other
devices connected to the same port from functioning correctly, if at
all.
- Driver page
-
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.
- Resources page
-
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 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.
The USB Root Hub Properties dialog includes the following pages:
- General page
-
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.
- Power page
-
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.
- Driver page
-
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.
- Power Management page
-
This page, not present in Windows 2000, contains only two checkboxes:
- Allow the computer to turn off this device to save power
-
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
Device Manager to the peripheral appearing to be recognized properly
but simply not working.
- Allow this device to bring the computer out of standby
-
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 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 Device Manager, choose View  Resources by
Type, and expand the Interrupt request (IRQ) item, as shown in Figure 24-12.
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 Device
Manager to locate an unused interrupt, clear the Use
automatic settings checkbox, and assign the unused
interrupt to the HCI.
On this system, 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.
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