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Child Devices of the Display Adapter

A child device of the display adapter is a device on the display adapter that is enumerated as a child by the display miniport driver. All child devices of the display adapter are on-board; monitors and other external devices that connect to the display adapter are not considered child devices.

The display miniport driver's DxgkDdiQueryChildRelations function is responsible for enumerating child devices of the display adapter. During the enumeration, the display miniport driver assigns each child device a type and a hot-plug detection (HPD) awareness value. The type is one of the DXGK_CHILD_DEVICE_TYPE enumerators:

  • TypeVideoOutput

  • TypeOther

The HPD awareness value is one of the DXGK_CHILD_DEVICE_HPD_AWARENESS enumerators:

  • HpdAwarenessAlwaysConnected

  • HpdAwarenessInterruptible

  • HpdAwarenessPolled

The following table gives some examples of devices that have various types and HPD awareness values.

HpdAwarenessVideoOutputOther

AlwaysConnected

Output for integrated LCD panel on a desktop computer

TV tuner

cross bar switch

MPEG2 codec

Interruptible

DVI

HDMI

Output for integrated LCD panel on a portable computer

Polled

S-video

HD15

 

The operating system uses one of several strategies, depending on the HPD awareness value, to determine whether an external device is connected to a child device. The following table briefly describes how the operating system determines the connection status of devices with various HPD awareness values.

HpdAwarenessHow operating system determines connection status

AlwaysConnected

The operating system knows the child device is always present. No external device is ever connected to or disconnected from the child device.

Interruptible

The operating system is notified when an external display device is connected to or disconnected from the child device. (The display panel on a portable computer is considered connected when the lid is open and disconnected when the lid is closed.)

Polled

The operating system asks whether an external display device is connected to the child device.

 

 

 

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