See Also
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To create a device driver that recognizes the power states of a target device, you must first create a driver that advertises a non-COM-related device interface. This non-COM-related device interface, in turn, specifies that the device is power-managed.
You can advertise a device interface in the following ways:
- Define the interface in the
IClassvalue of the registry key used to activate the device.
- Define the
IClassvalue in the
Activeregistry key, using the
Initfunction of the device driver.
- Define the
IClassvalue, using the REGINI parameter of the
ActivateDeviceExfunction.
- Explicitly call the
AdvertiseInterfacefunction in the device driver.
For additional information on advertising a non-COM-related interface for power management, see Device Interface Notifications.
You can register a device driver for power management notifications by calling the RequestPowerNotificationsfunction and passing a handle to a message queue created exclusively for power management notifications. Do this only if your driver must respond to a power notification and can afford to incur the associated overhead. Typically, once a driver has been advertised as a power-aware driver, the driver need only process DeviceIoControlcalls from Power Manager.
Power Manager communicates to a device with I/O control codes. The following table shows the I/O control codes that Power Manager uses.
| Function | Description |
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Requests that the device inform Power Manager of supported power states, along with any associated characteristics. |
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Requests that the device update the power state information. |
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Checks whether the device is ready to enter a new device power state. |
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Requests that the device inform Power Manager of the current device power state. |
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Notifies the parent device to register all controlled devices. |
You can implement and use the optional IOCTL_POWER_QUERYcontrol code to delay power state transitions until a driver has completed preparation for a change in power state. Do this by modifying the MDD layer to support IOCTL_POWER_QUERY, although this modification may make the MDD layer incompatible with future versions of Power Manager.