1. Because USB devices are Plug and Play devices there is little that can be done to control or configure them. However, most USB problems can be traced to one or more of the following conditions, [Q310575]:
? Malfunctioning or incorrectly configured hardware
? Malfunctioning, incorrectly configured, or missing device driver
? Mismatched cabling
? Out-of-date firmware or basic input/output system (BIOS)
? Improperly configured root hub
Note: The HKEY_LOCAL_MACHINE\Enum key contains subkeys for the specific hardware components installed on a system and Windows uses this information to allocate resources (for example, IO addresses and interrupts for the devices). All values in the Enum subkey are manufacturer- and device-specific, so specific information can vary from computer to computer.
2. Even though no USB devices are attached to a system, an icon is still displayed in the Notification Area which you may find entire unnecessary. Right-click within the Notification Area and then click Properties, Appearance tab, Advanced. On the Taskbar tab, click Customize and select Safely remove hardware. In the Behavior column, click Always hide.
3. Problems can arise when a new USB device is installed or when other changes are made to the system that affect a USB device. WinXP provides error messages when certain USB error conditions are encountered. Adding a USB device might cause a system to stop responding and if resetting the computer does not solve the problem, turn off the computer and try restarting it. If startup or stability problems persist, try any of the following troubleshooting suggestions:
a. Follow the manufacturer's installation instructions for the USB device. Some installations require that you run a setup program before plugging the device into your computer.
b. Plug the device into another computer to make sure that the problem is not due to your computer configuration. If you can reproduce the problem, the USB device might be malfunctioning.
c. If the device is attached to a USB hub, unplug it from the hub and reconnect it. Turn the hub off and on or connect the device directly to a free USB port on the computer.
d. Check the Event Log for USB-related error messages. The message can provide clues or other valuable information about the problem.
e. Check Device Manager to make sure that all devices on the Universal Serial bus controllers tree are functioning properly. Setting Device Manager to show USB devices by connection is usually the easiest way to spot a faulty device. Check that the device is not disabled. If a yellow exclamation point precedes a device, check Windows Update or contact your hardware vendor to obtain the most recent, compatible driver.
f. Verify that you are not exceeding USB power limits. If a USB device attempts to draw more than 500 milliamps (mA) of electrical current, the device must be accompanied by a wall adapter to draw the additional power. If you are unsure about total USB power consumption for your system, use the power supply if one is furnished with your device to guarantee adequate power (Open Device Manager, and then expand Universal Serial Bus controllers, double-click USB Root Hub, click the Power Management tab to view information about power consumption).
g. The USB specification allows up to five external hubs to be connected in a chain.
h. Always use the cables included with the device and replace damaged or worn cables with an identical type. USB cables come in many kinds and lengths, depending on the capability of the device. Using incorrect cables can degrade performance or cause the device to stop functioning.
Note: When installing a USB device, and an appropriate driver exists in the Driver.cab file, the device is configured without the operating system requesting a device driver. However, some USB devices might not be supported with WinXP and when WinXP or you attempt to install an unsupported device, the system may prompt for the appropriate driver which you will have to supply by selecting the location on removable media containing the drivers supplied by the device manufacturer, [Q314636].
4. The USB error detection and correction scheme uses ''WMI'' event-driven architecture to resolve errors. The interface usually notifies a user when a problem occurs on the bus, gives information about the error, and suggests solutions. When an error message is clicked, a dialog box appears showing the following, [Q308423]:
a. A description of the error condition.
b. The tree-view, which is a topological view of the bus. The tree is expanded so that the device in question is displayed, selected, and in bold.
c. A recommended user action, which depends on the current topology of devices on the bus.
5. The following six error conditions reported for USB devices result in messages that give error descriptions, and some also give troubleshooting advice:
a. Electrical surge on hub port - either a device attached to the port, or the port itself, has drawn more current than allowed, and the hub turned off the port. The port will not function correctly until you reset it. If the device is the cause, it must be detached before resetting the port. To reset the port, disconnect the device, and then click Reset in the dialog box. If the port is the cause, close the dialog box, and do the following to re-enable the port:
? Disconnect the hub.
? Re-attach the hub.
Note: If it is the root hub, unplug all attached USB devices from the computer, and (if they have power supplies) unplug them from the electric supply. After a few moments, reconnect the devices. The computer can be restarted at any time.
b. USB hub port power exceeded - a device that requires more than 100 mA has been plugged into a bus-powered hub that can supply only 100 mA to each of its ports. The device will not work until it is plugged into a self-powered hub, or into a root hub, that supplies 500 mA to each port. Disconnect the problem device and reconnect it to an unused port that meets its power requirements. (The error dialog box lists the appropriate port in bold.)
c. USB host controller bandwidth exceeded - a device request for allocation of bandwidth has failed because the USB host controller is in full use and has no spare bandwidth. Typically, devices support several settings at various levels of bandwidth. A device tries to allocate the highest bandwidth, progressively metering itself back after each bandwidth allocation fails. Repeated requests trigger an error condition.
Note: It is recommended that you close some applications that are using USB devices that use bandwidth. In Device Manager you can view the property page for the host controller to see bandwidth status. Pressing Refresh in the dialog box after making any changes updates bandwidth data to show whether bandwidth is freed.
d. Maximum number of hubs surpassed - six or more USB hubs are linked in a chain, and the USB specification allows a maximum of five. It is recommended that you remove the most recently connected hub and connect it to a port that is highlighted on the tree view list in green (signifying that it is free and recommended).
e. Device enumeration failure - a device is plugged into a USB port, but the operating system does not recognize the device. The failure can have various causes. For example, the device might not initialize properly when it is plugged in, or the device driver might be faulty. If the cause is not a permanent malfunction in the physical device, unplugging and plugging the device in again might allow it to enumerate properly.
f. Identical serial numbers - the serial number in a device, if it exists, must be unique for each device that shares the same USB Vendor ID and Product ID. Occasionally hardware vendors mistakenly program devices with identical serial numbers. When two or more USB devices with identical serial numbers are plugged into the same system, only the first one plugged in functions.
6. USB hubs can be built that operate in either self-powered or bus-powered mode. Self-powered hubs draw their power from the electrical outlet, while bus-powered hubs draw their power from the USB bus. From the aspect of user experience, hubs operating in self-powered mode have a significant advantage over hubs operating in bus-powered mode for the following reasons:
a. A user can plug any bus-powered USB device into any port on a self-powered hub, and the device will always have enough power to function. The power needed by a bus-powered USB device in order to function can range from a few mA up to a maximum of 500mA.
b. A user can plug a bus-powered USB device into a port on a bus-powered hub, but the device might not have enough power to function. Specifically:
c. Only low-power bus-powered devices are guaranteed to have enough power available from a bus-powered hub port to operate (section 7.2.1 of USB Specification, Version 1.1). Low-power bus-powered devices draw less than 100mA when fully operational. To meet the specification, a bus-powered hub must supply up to 100mA at each port, but must not supply more than 100mA. Typical low-power bus-powered USB devices include mice, keyboards, and other HID devices.
d. A large number of USB devices require between 100mA and 500mA from the hub port when fully operational. These devices will not operate when the user plugs them into a port on a bus-powered hub. Examples of high-power bus-powered devices that will not work with a bus-powered hub include video cameras, page scanners, and floppy disk drives.
Warning: Even if it seems unlikely that a user would use USB for a high-power device, the problem with bus-powered USB hub designs is the user's expectation that any USB device can be plugged into any hub and it will work. This is not true with bus-powered hub designs.
7. Any of the following symptons may be experienced and can occur because WinXP does not include support for EHCI host controllers, (Universal Serial Bus 2.0 Support in Windows XP (Q312370)):
? A Hi-Speed Universal Serial Bus (USB) 2.0 device does not operate in Hi-Speed mode.
? Using a Hi-Speed USB 2.0 device produce any of the following warnings:
The Generic USB Hub is a HI-SPEED USB device and will function at reduced speed when plugged into a non-HI-SPEED port.
HI-SPEED USB Device Plugged into non-HI-SPEED USB Hub. A HI-SPEED USB device is plugged into a non-HI-SPEED USB hub.
8. An Enhanced Host Controller Interface-compliant (EHCI-compliant) USB host controller appears in Device Manager with an exclamation point in a yellow circle, or with status code 28.
Note: To resolve this problem, obtain the latest ''Service Pack'' for WinXP.
9. Device Manager displays only non-Plug and Play devices, drivers, and printers. Devices that were installed and not connected (such as a Universal Serial Bus [USB] device or ''ghosted'' devices) are not displayed in Device Manager even when clicking Show hidden devices, [Q315539].
10. The System Information (Msinfo32.exe) Tool [Q308549] collects system information on a system such as devices that are installed or device drivers that are loaded and provides a menu for displaying the associated system topics that can be used to diagnose issues. Use System Information to determine what adapters are installed and to view the status of its drivers.
11. In WinXP, USB devices using a SCSI-to-USB adapter are displayed as ''USB SCSI Storage Device'' in the Safely Remove Hardware icon in the taskbar. Finding and identifying a device to remove may be confusing when multiple devices are installed. To see the actual storage device names, open the Safely Remove Hardware dialog box and then click to select the Display Device Components box. [Q292750].
a. Some Plug and Play devices can be installed or removed while the system is running. For example, USB, IEEE 1394 (serial) and PC Card devices can be added to and removed from a fully powered system. When such hardware is added or removed, the operating system automatically detects insertion or removal of the device and manages system and/or hardware configuration as required.
b. If the Safety Remove Hardware (SRH) icon appears in the notification area next to the task bar, double-click the icon to displays a list of Plug and Play devices currently attached that supports safe removal. The SRH application informs Windows that the user intends to remove a device and gives Windows an opportunity to prepare for the removal by taking steps such as halting data transfers to the device and unloading device drivers.
c. Surprise removal is generally referred to when hardware is removed from a running system without using the SRH application because the operating system is not notified in advance. Surprise removal is particularly a concern for storage devices for which write caching is enabled, because when such devices are surprise removed, data loss or corruption might occur. To reduce the likelihood of data loss or corruption due to surprise removal of consumer oriented storage devices, WinXP disables write caching by default for these devices (such as cameras that include IEEE 1394 or USB storage, small form factor storage devices such as compact flash, and so on). While write caching policy addresses this particular issue, it is recommended that users continue to use the SRH application when it appears in the notification area. Also, disabling write caching might slow the performance of consumer oriented storage devices.
d. Before removing a device from a bus that supports hot plugging, check to see if the SRH icon appears in the notification area. If it does, it is recommended it be used to notify the operating system that the device is about to be unplugged. Click the SRH icon in the notification area to displays a notification bubble with a list of devices currently attached and then click the device to remove. Click Stop, and then click OK, to inform the system that a device is being unplugged or ejected.
Note: If it is nearly impossible to determine what the device name represents, open the SRH dialog box and then click to select the Display Device Components box to see the name(s).
e. To unplug or eject devices:
? In the notification area next to your task bar, double-click the Safe Removal icon which displays a list of Plug and Play devices that support safe removal and that are currently attached to the system. If you do not see this icon, your device does not support safe removal, and you cannot unplug or eject your device using this feature.
? In Safely Remove Hardware, in the list of devices, select the device that you want to unplug or eject, and then click Stop which tells the system that you will be unplugging or ejecting the device.
? In Stop a Hardware device, click OK (a notification appears stating that it is now safe to unplug or eject the device).
f. To start and stop non-Plug and Play drivers
? Open Device Manager (click Start, Control Panel, double-click Administrative Tools, Computer Management), click the View menu, and then click Show hidden devices.
? In the list of devices, double-click Non-Plug and Play Drivers, right-click a device, and then click Properties. On the Driver tab, click Start or Stop to start or stop the device driver, and then click OK.
Note: If the Start button on the Driver tab is unavailable, the driver is already loaded.
g. Supplemental reading:
(1) ''Your Computer May Stop Responding After You Remove Either a CD-ROM Drive or a DVD Drive from the Drive Bay (Q310664).''
(2) ''You Cannot View the Files on a Disc After You Replace a CD-R or CD-RW Drive with a DVD or CD-ROM Drive (Q311455).''
(3) ''Computer May Hang When You Swap a CardBus Card After Resuming from Suspend (Q318358).''
(4) ''Programming of Transfer Mode Speed Is Not Supported by Atapi.sys When You Hot or Warm Swap Drives (Q323760).''
12. The article [Q329632] describes the availability of Universal Serial Bus (USB) 2.0 driver support in Microsoft Windows XP Service Pack 1 and discusses four very important steps for upgrading.
13. Supplemental reading:
a. ''USB 3.5-inch Floppy Disk Drive Listed As 5.25-Inch in Safe Mode (Q303024).''
b. ''After You Install a Visioneer USB Scanner the CPU Usage May Be Unusually High (Q303777).''
c. ''HAL Options After Windows XP Setup (Q309283).''
d. ''Universal Serial Bus Devices Do Not Work in Safe Mode (Q310496).''
e. ''USB Power Exceeded'' Error Message When Connecting USB Devices (Q310591).''
f. ''Windows XP Does Not Detect Your New USB Device (Q314634).''
g. ''Computer Does Not Shut Down Properly if Selective Suspend Is Enabled (Q315664).''
h. ''Your IEEE 1394 or USB CD-ROM or DVD-ROM Drive May Not Be Recognized in Windows XP (Q323507).''
i. ''Your USB Keyboard and Mouse That Are Connected to a USB 2.0 Controller Are Slow to Respond After Hibernation (Q810063).''
j. ''Universal Serial Bus Devices Are Not Detected Intermittently When You Start or Resume the Computer (Q810090).''
k. ''Universal Serial Bus Mouse Does Not Work (Q817581).''
l. ''When you install Windows XP Service Pack 2, the USB 2.0 drivers do not appear to update (Q873169)'' and ''USB device does not function after connecting device to Windows XP Service Pack 2-based computer (Q870893).''
14. ''Check this USB site.''
15. ''Search the MSDN library'' using this link and enter the search parameter windows xp. After this list is received, enter USB in the box labeled, Show within the results found just to the right of that list, and then press Enter -- there are hundreds of articles concerning individual devices covered in the database. Else, use the Knowledge Base search using this ''link'', and enter information in the Search for... box. If you rather use ''All words'', then switch the parameters in the next box.
Note: Clicking this link opens the linked-site in a separate window for your convenience, and once open, any item of interest should be opened in a separate window for viewing/reading. After finishing, simply close that window and you'll pop right back to the main list which requires no refresh -- regenerating a window, which has been written over and progressed back to, can be time consuming as you may well know.