AnandTech: Intel Core Duo USB Issue: A Mischaracterized Bug

The Fix

The Microsoft Knowledge Base article that references the USB power drain problem also provides a solution to the problem, a simple registry edit that prevents the USB devices from keeping the processor from moving to lower power states. The entire text of the KB article was actually anonymously posted in a Slashdot thread, and thus, is now publicly available. As with any changes to your Windows Registry, be sure to hang onto a backup copy and make any modifications at your own risk:

A Windows XP SP2-based portable computer uses its battery power more quickly than you expect when a USB 2.0 device is connected

View products that this article applies to.

Partner Only Article Article ID : 899179

Last Review : July 12, 2005

Revision : 1.0

Important: This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 (https://premier.microsoft.com/kb/256986/) Description of the Microsoft Windows registry

SYMPTOMS

Consider the following scenario. You install Microsoft Windows XP Service Pack 2 (SP2) on a portable computer. Then, you connect a USB 2.0 device to the computer. In this scenario, the computer uses its battery power more quickly than you expect.

CAUSE

Windows XP SP2 installs a USB 2.0 driver that initializes any connected USB device. However, the USB 2.0 driver leaves the asynchronous scheduler component continuously running. This problem causes continuous instances of memory access that prevent the computer from entering the deeper Advanced Configuration and Power Interface (ACPI) processor idle sleep states. These processor idle sleep states are also known as C states. For example, these include the C3 and C4 states. These sleep states are designed, in part, to save battery power. If an otherwise idle portable computer cannot enter or maintain the processor idle sleep states, the computer uses its battery power more quickly than you expect.

RESOLUTION

Warning: Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk. To resolve this problem, add the EnIdleEndpointSupport entry to the USB registry key. To do this, follow these steps:
Click Start, click Run, type regedit, and then click OK.

Locate, and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\USB

Note: If the USB subkey does not exist, create it. To do this, follow these steps:
a. Select the Services key. On the Edit menu, point to New, and then click Key.
b. Type USB in the New Key #1 box to name the new key "USB."

Right-click USB, point to New, and then click DWORD Value.

In the New Value #1 box that appears, type EnIdleEndpointSupport, and then press ENTER.

Right-click EnIdleEndpointSupport, and then click Modify.

In the Value data box, type 1, leave the Hexadecimal option selected, and then click OK.

Quit Registry Editor.
STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

APPLIES TO

Microsoft Windows XP Service Pack 2, when used with:
Microsoft Windows XP Professional

Microsoft Windows XP Home Edition

Unfortunately, the solution isn't completely ready for public deployment, as there are apparently still some scenarios where it doesn't fix the problem. There may be issues with the problem re-appearing after putting your system to sleep, which are presently being worked on. However, for the majority of situations, this simple registry modification should, in theory, take care of things. With the solution in hand, and five notebooks to play with, we went to work.