RG82855GMESL72L Datasheet, PDF (57/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Register Description
R
Bit
31
30:24
23:16
15:11
10:8
7:2
1:0
Description
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.
Reserved
Bus Number: When the Bus Number is programmed to 00h, the target of the Configuration Cycle is
a Hub interface agent (GMCH, ICH4-M, etc.).
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).
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].
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.
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.
Reserved
4.6.2 CONFIG_DATA – Configuration Data Register
I/O Address:
Default Value:
Access:
Size:
0CFCh
00000000h
Read/Write
32 bits
CONFIG_DATA is a 32-bit Read/Write window into Configuration Space. The portion of
Configuration Space that is referenced by CONFIG_DATA is determined by the contents of
CONFIG_ADDRESS.
Figure 4. Configuration Data Register
31
0
0
Bit
Default
Configuration Data Window
Datasheet
57