Microsoft KB Archive/297045

= The Laptop Computer May Be Unable to Enter the C3 Processor Power-Saving State =

Article ID: 297045

Article Last Modified on 2/28/2007

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APPLIES TO


 * Microsoft Windows 2000 Service Pack 2
 * Microsoft Windows 2000 Service Pack 2
 * Microsoft Windows Millennium Edition
 * Microsoft Windows 98 Second Edition

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This article was previously published under Q297045



IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry



SYMPTOMS
Your laptop computer may be unable to enter the C3 processor power-saving state.



CAUSE
This problem can occur because the active bus polling that is required to maintain communication with universal serial bus (USB) devices can prevent the CPU from switching to a C3 power-saving state. By default, the USB polling interval is set for every one millisecond (ms). Even if no devices are connected to the USB controller, the polling operation is still performed and the processor cannot enter a C3 power-saving state.



RESOLUTION
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To resolve this problem, increase the USB polling interval from one ms to five ms. Then, the processor can enter a C3 power-saving state during its inactivity and extend the battery life of the computer. To increase this polling interval, add a registry entry that is dependent upon the operating system:

For Windows Millennium Edition
 Start Registry Editor (Regedit.exe). Locate and click the following key in the registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Usb\0000

 On the Edit menu, click New, click Edit, click DWORD Value, and then add the following registry value:

Value name: IdleEnable

Radix: Hexadecimal

Value data: 1

 Quit Registry Editor.

For Windows 2000
 Start Registry Editor (Regedt32.exe).</li> Locate and click the following key in the registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Class\{36FC9E60-C465-11CF-8056-444553540000}\0000

</li> Look for the registry value named Controller in this key. If this value is not present, proceed to step 5; otherwise, continue on to step 4.</li> On the Edit menu, click Add Value, and then add the following registry value:

Value name: IdleEnable

Data type: REG_DWORD

Radix: Hexadecimal

Value data: 1

</li> If additional sequentially numbered keys after \0000 exist (for example, \0001, \0002, or \0003), repeat step 3 for each of them.</li> Quit Registry Editor.</li></ol>

<div class="moreinformation_section">

MORE INFORMATION
Battery-powered computers that use Advanced Power Management (APM) or Advanced Configuration and Power Interface (ACPI) may experience increased power consumption leading to a more rapid drain of battery power. This type of problem only occurs on computers that use an OHCI USB controller.

Keywords: kbenv kbprb KB297045

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