IWDFDevice2::GetSystemPowerAction method

The GetSystemPowerAction method returns the system power action, if any, that is currently occurring for the computer.

Syntax

C++


POWER_ACTION GetSystemPowerAction();

Parameters

This method has no parameters.

Return value

GetSystemPowerAction returns a POWER_ACTION-typed enumerator value. The value indicates the system power action that is currently occurring for the computer. For more information, see the following Remarks section.

Remarks

The GetSystemPowerAction method enables a driver to determine whether a device's power transition is occurring because the device is idle (or waking up), or because the entire computer is entering (or leaving) a low-power state.

The driver must call GetSystemPowerAction only from the event callback functions that the framework calls when the device is entering a low-power state or returning to its working state.

The value that GetSystemPowerAction returns depends on the following situations:

If the computer is entering a low-power state when the driver calls GetSystemPowerAction, the method returns the reason that the computer is entering the low-power state. For example, the method returns PowerActionSleep if the computer is entering its S1, S2, or S3 low-power state.
If the computer is returning to its working (S0) state from a low-power state when the driver calls GetSystemPowerAction, the method returns the reason that the computer entered the low-power state. For example, the method returns PowerActionSleep if the computer is leaving its S1, S2, or S3 low-power state.
If the computer is powering up (after having been turned off) when the driver calls GetSystemPowerAction, the method returns PowerActionNone.
If the device is entering a low-power idle state or returning to its working (D0) state when the driver calls GetSystemPowerAction, while the rest of the system remains at its working (S0) state, the method returns PowerActionNone.
If the computer and the device are both in their working states when the driver calls GetSystemPowerAction, the method returns PowerActionNone.

For more information about low-power states, see A Device Enters a Low-Power State.

Examples

The following code example obtains the IWDFDevice2 interface and then calls GetSystemPowerAction.


   IWDFDevice2 *pDevice2 = NULL;
    HRESULT hrQI = pDevice->QueryInterface(IID_PPV_ARGS(&pDevice2));
    if (SUCCEEDED(hrQI))
    {
        POWER_ACTION powerAction = pDevice2->GetSystemPowerAction();
    }
...
    SAFE_RELEASE(pDevice2);

Requirements

End of support	Unavailable in UMDF 2.0 and later.
Minimum UMDF version	1.9
Header	Wudfddi.h (include Wudfddi.h)
DLL	WUDFx.dll