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

Article ID: 297045 - View products that this article applies to.

This article was previously published under Q297045

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SYMPTOMS

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

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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.

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RESOLUTION

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756

(http://support.microsoft.com/kb/322756/ )

How to back up and restore the registry in Windows

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).
Locate and click the following key in the registry:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Class\{36FC9E60-C465-11CF-8056-444553540000}\0000
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.
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
If additional sequentially numbered keys after \0000 exist (for example, \0001, \0002, or \0003), repeat step 3 for each of them.
Quit Registry Editor.

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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.

Note If you use Windows Vista, you can visit the following Microsoft Web page for help with power consumption and battery life problems:

Fix problems in which power consumption is more than expected or the battery life is short

(http://support.microsoft.com/gp/windows_battery_power_settings)

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