Power-Manageable Device Drivers

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:

  • You can define the interface in the IClass value of the registry key used to activate the device.
  • You can define the IClass value in the Active registry key using the Init function of the device driver.
  • You can define the IClass value using the REGINI parameter for the ActivateDeviceEx function.
  • You can explicitly call the AdvertiseInterface function 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 RequestPowerNotifications function and passing a handle to a message queue created exclusively for power management notifications. You should only do this 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 needs only to process DeviceIoControl calls from the Power Manager.

The Power Manager communicates to a device with IOCTL codes. The following table shows the IOCTL codes the Power Manager uses to communicate with a device.

Function Description
IOCTL_POWER_CAPABILITIES Requests that the device inform the Power Manager of supported power states along with any associated characteristics.
IOCTL_POWER_SET Requests that the device update the power state information.
IOCTL_POWER_QUERY Queries to verify that the device is ready to enter a new device power state.
IOCTL_POWER_GET Requests that the device inform the Power Manager of the current device power state.
IOCTL_REGISTER_POWER_RELATIONSHIP Notifies the parent device to register all controlled devices.

You can implement and use the optional IOCTL_POWER_QUERY control code as a way to delay power state transitions until a driver has completed preparation for a change in power state. You can 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 the Power Manager.

See Also


 Last updated on Tuesday, May 18, 2004

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