The ComponentActiveConditionCallback callback routine notifies the driver that the specified component completed a transition from the idle condition to the active condition.



void PoFxComponentActiveConditionCallback(
  PVOID Context,
  ULONG Component



A pointer to the device context. The device driver uses this context to store information about the current power state of the device. The device driver specified this pointer in the DeviceContext member of the PO_FX_DEVICE structure that the driver used to register the device with the power management framework (PoFx). This context is opaque to PoFx.


Specifies the index that identifies the component. This parameter is an index into the Components array in the PO_FX_DEVICE structure that the device driver used to register the device with PoFx. If the Components array contains N elements, component indexes range from 0 to N–1.

Return Value



A component's hardware registers can be accessed only when the component is in the active condition. Do not rely on the Fx power state of a component to determine whether the component can be accessed. If the component is in the F0 state and is in the idle condition, the component might be about to switch to another Fx state.

To gain access to a component that is in the idle condition, the driver can call the PoFxActivateComponent routine to switch the component to the active condition. If the component is not already in the active condition when PoFxActivateComponent is called, PoFx initiates the transition to the active condition, and then calls the ComponentActiveConditionCallback routine to notify the driver when the transition is complete.

The driver receives a ComponentActiveConditionCallback callback whenever the component completes a transition to the active condition, regardless of whether the driver called PoFxActivateComponent to initiate the transition. For example, the Windows kernel might activate the component on behalf of the driver before sending a Plug and Play IRP or a system set-power IRP to the driver.


To define a ComponentActiveConditionCallback callback routine, you must first provide a function declaration that identifies the type of callback routine you're defining. Windows provides a set of callback function types for drivers. Declaring a function using the callback function types helps Code Analysis for Drivers, Static Driver Verifier (SDV), and other verification tools find errors, and it's a requirement for writing drivers for the Windows operating system.

For example, to define a ComponentActiveConditionCallback callback routine that is named MyComponentActiveConditionCallback, use the PO_FX_COMPONENT_ACTIVE_CONDITION_CALLBACK type as shown in this code example:

Then, implement your callback routine as follows:
    PVOID Context,
    ULONG Component
      // Function body
The PO_FX_COMPONENT_ACTIVE_CONDITION_CALLBACK function type is defined in the Wdm.h header file. To more accurately identify errors when you run the code analysis tools, be sure to add the Use_decl_annotations annotation to your function definition. The Use_decl_annotations annotation ensures that the annotations that are applied to the PO_FX_COMPONENT_ACTIVE_CONDITION_CALLBACK function type in the header file are used. For more information about the requirements for function declarations, see Declaring Functions by Using Function Role Types for WDM Drivers. For information about Use_decl_annotations, see Annotating Function Behavior.


Windows version Supported starting with Windows 8. Supported starting with Windows 8.
Target Platform Desktop
Header wdm.h

See Also



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