Problems may occur when you try to transfer files to or from a device that is connected to a USB 2.0 hub in Windows 7


For the Windows XP and Windows Vista version of this article, please see http://support.microsoft.com/kb/908673.

Symptoms


You try to transfer files to or from a device that is connected to a USB 2.0 hub in Windows 7. When you do this, you may experience one or more of the following symptoms: 
  • The file transfer fails. You may receive an error message about a delayed write failure. The error message that you receive may vary, depending on the device that you are using.
  • Other USB devices that are connected to the USB 2.0 hub may stop working. You may receive a message that states that the USB devices were disconnected or reconnected.
  • Power may be disabled on USB devices. Then, the devices are re-enumerated.
  • A USB keyboard may stop working correctly. For example, the behavior of keys may be irregular. When you press a key, the key entry may be repeated many times. Or, when you press a key, nothing may occur. 

Note Some computers have an internal USB 2.0 hub. For example, a portable computer may have a single USB bus and may use an internal USB hub to provide two or more available USB ports on the computer. Therefore, this issue may occur if the device is connected directly to a USB port on the computer.

This issue might also occur if the device is internal and is connected internally to the internal USB 2.0 hub. For example, this problem might occur if you use a portable computer that has an internal Bluetooth radio that is connected to an internal USB 2.0 hub. When you use the Bluetooth device to transfer the files to another device, you may experience any of the symptoms that are described in this section.

Cause


This problem can occur when there is a large amount of traffic on the USB 2.0 hub, and you transfer files to a low-speed or full-speed USB device. The problem does not occur when you transfer files to a high-speed USB device. 

For more information about USB 2.0 data transfer rates, see "More Information" 

Additionally, this problem has been observed on computers that use Transmeta processors (CPUs).

Resolution


Set the EnHcSoftRetry registry entry under the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\PCI\<hw id>\<instance id>\Device Parameters
The registry entry is configured to have a DWORD value of 1. This value enables the Soft-Retry code path that works around this issue.

Note To obtain <hw id> and <instance id>, open the property page in Device Manager for each EHCI USB host controller, click the Details tab, and then select Device Instance Path from the list. Most systems have only one or two EHCI host controllers, so this should not be difficult. 

More Information


Data transfer rates for USB 2.0

USB 2.0 supports the following maximum data transfer rates, depending on how much bus bandwidth a device requires: 
  • 1.5 megabits per second (Mbps) for low-speed devices that do not require lots of bandwidth. These devices include mouse devices and keyboards.
  • 12 Mbps for full-speed, higher-performing devices. These devices include storage devices, speakers, scanners, and video cameras.
  • 480 Mbps for high-speed devices. These devices include mass storage devices and Hi-Speed CD or DVD recorders.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates