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User Control of Device Idle and Wake Behavior

  • Cikk

If a device has idle power-down or wake-up capabilities, you can decide whether users should be allowed to enable or disable these capabilities.

Your driver can use members of the WDF_DEVICE_POWER_POLICY_IDLE_SETTINGS structure to specify whether users with registry access can enable or disable a device's idle power-down capability.

Your driver can use members of the WDF_DEVICE_POWER_POLICY_WAKE_SETTINGS structure to specify whether users with registry access can enable or disable a device's wake-up capability.

Both of these structures allow the driver to enable the capability, disable the capability, or give users control of the capability. To give users control, in the appropriate settings structure the driver sets the UserControlOfIdleSettings or UserControlOfWakeSettings member to IdleAllowUserControl or WakeAllowUserControl, respectively, and the Enabled member to WdfTrue or WdfUseDefault,.

If your driver allows users to modify idle and wake settings, the framework provides a user interface, in the form of a property sheet page that Device Manager displays so that users can enable or disable the idle and wake capabilities. (The framework modifies IdleInWorkingState and WakeFromSleepState registry values. Drivers and their installation files must not read or modify these values.)

If a user modifies a device's settings, the framework updates the device's power state to match the new settings, if necessary. For example, if the user disables a device's idle power-down capability while the device is already in a low-power state because it was idle, the framework returns the device to its working state.

If your driver allows users to modify idle and wake settings, the framework enables these settings by default. Some driver writers might want to initially disable the settings before allowing users to modify them.

Therefore, for version 1.9 and later versions of KMDF, the framework provides two driver-definable registry values, named WdfDefaultIdleInWorkingState and WdfDefaultWakeFromSleepState, which are stored in the device's Device Parameters\WDF subkey, under the device's hardware key. The values are REG_DWORD-typed, with "0" indicating the capability is disabled and "1" indicating the capability is enabled.

Your driver's INF file can use an INF AddReg directive to create and set the WdfDefaultIdleInWorkingState and WdfDefaultWakeFromSleepState registry values. For example, if your driver enables a device's idle power-down capability, but if the capability must be disabled when the device is installed, the driver's INF file can set WdfDefaultIdleInWorkingState to "0".

The framework examines the WdfDefaultIdleInWorkingState and WdfDefaultWakeFromSleepState registry values only if the driver has set the UserControlOfIdleSettings or UserControlOfWakeSettings member to IdleAllowUserControl or WakeAllowUserControl, respectively, and the Enabled member to WdfTrue or WdfUseDefault, in the appropriate settings structure.