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.
| HpdAwareness | VideoOutput | Other |
|---|---|---|
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.
| HpdAwareness | How 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. |