Register Description
R
Intel
®
82925X/82925XE MCH Datasheet 43
3.4 I/O Mapped Registers
The MCH contains two registers that reside in the processor I/O address space − the
Configuration Address (CONFIG_ADDRESS) Register and the Configuration Data
(CONFIG_DATA) Register. The Configuration Address Register enables/disables the
configuration space and determines what portion of configuration space is visible through the
Configuration Data window.
3.4.1 CONFIG_ADDRESS—Configuration Address Register
I/O Address: 0CF8h Accessed as a DWord
Default Value: 00000000h
Access: R/W
Size: 32 bits
CONFIG_ADDRESS is a 32-bit register that can be accessed only as a DW. A Byte or Word
reference will "pass through" the Configuration Address Register and DMI onto the Primary PCI
bus as an I/O cycle. The CONFIG_ADDRESS register contains the Bus Number, Device
Number, Function Number, and Register Number for which a subsequent configuration access is
intended.
Bit Access
&
Default
Description
31 R/W
0b
Configuration Enable (CFGE):
1 = Enable
0 = Disable
30:24 Reserved
23:16 R/W
00h
Bus Number: If the Bus Number is programmed to 00h the target of the
Configuration Cycle is a PCI Bus #0 agent. If this is the case and the MCH is not
the target (i.e., the device number is ≥ 3 and not equal to 7), then a DMI Type 0
Configuration Cycle is generated.
If the Bus Number is non-zero, and does not fall within the ranges enumerated by
device 1’s Secondary Bus Number or Subordinate Bus Number Register, then a
DMI Type 1 Configuration Cycle is generated.
If the Bus Number is non-zero and matches the value programmed into the
Secondary Bus Number Register of device 1, a Type 0 PCI configuration cycle will
be generated on PCI Express Graphics.
If the Bus Number is non-zero, greater than the value in the Secondary Bus
Number register of device 1 and less than or equal to the value programmed into
the Subordinate Bus Number Register of device 1 a Type 1 PCI configuration
cycle will be generated on PCI Express Graphics.
This field is mapped to byte 8 [7:0] of the request header format during PCI
Express Configuration cycles and A[23:16] during the DMI Type 1 configuration
cycles.
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