Intel D15343-003 manual Bit Descriptions, Reserved

Intel® 82854 Graphics Memory Controller Hub (GMCH)

Bit	Descriptions
31	Configuration Enable (CFGE): When this bit is set to 1, accesses to PCI Configuration Space
	are enabled. If this bit is Reset to 0, accesses to PCI Configuration Space are disabled.
30:24	Reserved
23:16	Bus Number: When the Bus Number is programmed to 00h, the target of the Configuration
	Cycle is a Hub interface agent (GMCH, ICH4-M, and so on.).
	The Configuration Cycle is forwarded to Hub interface if the Bus Number is programmed to 00h
	and the GMCH is not the target (the device number is >= 2).
15:11	Device Number: This field selects one agent on the PCI Bus selected by the Bus Number. When
	the Bus Number field is 00 the GMCH decodes the Device Number field. The GMCH is always
	Device Number 0 for the Host-Hub interface bridge entity. Therefore, when the Bus Number =0
	and the Device Number=0-1 the internal GMCH devices are selected.
	For Bus Numbers resulting in Hub interface Configuration cycles, the GMCH propagates the
	device number field as A[15:11].
10:8	Function Number: This field is mapped to A[10:8] during Hub interface Configuration cycles.
	This allows the configuration registers of a particular function in a multi-function device to be
	accessed. The GMCH ignores Configuration cycles to its internal Devices if the function number is
	not equal to 0.
7:2	Register Number: This field selects one register within a particular Bus, Device, and Function as
	specified by the other fields in the Configuration Address register. This field is mapped to A[7:2]
	during Hub interface Configuration cycles.
1:0	Reserved

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