Description of how to enable the S3 system power state for standby when USB devices are armed for wake (841858)

INTRODUCTION

By default, Microsoft Windows XP and Microsoft Windows Server 2003 enable a universal serial bus (USB) keyboard and a USB mouse to wake a computer after the computer goes in hibernation. Other types of USB devices can be enabled to wake the computer if you click to select the Allow this device to bring the computer out of standby check box. You can click to select this check box on the Power Management property page in Device Manager.

When a USB device is enabled to wake the computer, the default behavior permits the computer to enter the S1 system power state for standby. Standby is not the S3 system power state. The S1 system power state is a "lighter" system power state than S3. The S1 system power state typically conserves less power than the S3 system power state.

By using the following registry entry, you can override entering the S1 system power state as a default behavior when a USB device is enabled to wake the computer:

USBBIOSx

MORE INFORMATION

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.

The basic input/output system (BIOS) reports the wake capabilities of an on-board device, such as a USB host controller. Some systems report that "wake" from the S3 system power state for their on-board USB host controller is supported. However, problems may occur when these other systems try to use wake from the S3 system power state for their on-board USB host controller. These problems include the following:

Loss of power during the S3 system power state on the USB
False device removal and false arrival notifications upon resume from standby
Reset of attached USB devices during suspend and resume
Failure to resume fully from the S3 system power state

To prevent a negative end-user experience, Windows XP and Windows Server 2003 modify the power capabilities that are returned by the BIOS. Therefore, the system only supports wake by using the USB for the S1 system power state. If there is no USB device that is armed for wake from a system power state, the system enters the S3 system power state during standby. For systems that correctly support wake by use of the USB from the S3 system power state, this behavior can be modified by using the following registry entry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usb
"USBBIOSx"=DWORD:00000000

Note Values other than 0x00000000 for USBBIOSx are reserved for future use. Do not use values other than 0x00000000 for USBBIOSx.

The USBBIOSx registry value is applied globally to all USB host controllers in the system. The BIOS reports the wake capabilities of all attached USB host controllers.

Installation of a third-party add-in USB host controller card when the USBBIOSx value is set to 0x00000000 may cause problems with waking the computer through that controller.

Note Another similar USB-specific registry value that is named USBBIOSHacks is unsupported and must not be used.

The USBBIOSx registry value is intended for use by computer manufacturers when they pre-install Windows XP or Windows Server 2003 on their computers. We do not recommend that end-users set this registry value. We do not recommend that USB hardware vendors try to set this value during installation of their USB device.