Intel
82865G/82865GV GMCH Datasheet
51
Register Description
Cycle. A[1:0] of the HI request packet for the Type 1 configuration cycle is 01. Bits 31:2 of the
CONFIG_ADDRESS register are translated to the A[31:2] field of the HI request packet of the
configuration cycle as shown in
Figure 7
. This HI configuration cycle is sent over HI.
If the cycle is forwarded to the ICH5 via HI, the ICH5 compares the non-zero Bus Number with the
Secondary Bus Number and Subordinate Bus Number registers of its PCI-to-PCI bridges to
determine if the configuration cycle is meant for Primary PCI, one of the ICH5’s HIs, or a
downstream PCI bus.
3.3.4
AGP/PCI_B Bus Configuration Mechanism
From the chipset configuration perspective, AGP/PCI_B is seen as PCI bus interfaces residing on a
Secondary Bus side of the virtual PCI-to-PCI bridges referred to as the GMCH Host-PCI_B/AGP
bridge. On the Primary bus side, the virtual PCI-to-PCI bridge is attached to PCI Bus 0. Therefore,
the Primary Bus Number register is hardwired to 0. The virtual PCI-to-PCI bridge entity converts
Type 1 PCI Bus Configuration cycles on PCI Bus 0 into Type 0 or Type 1 configuration cycles on
the AGP/PCI_B interface. Type 1 configuration cycles on PCI Bus 0 that have a Bus Number that
matches the Secondary Bus Number of the GMCH’s “virtual” Host-to-PCI_B/AGP bridge are
translated into Type 0 configuration cycles on the PCI_B/AGP interface. The GMCH decodes the
Device Number field [15:11] and assert the appropriate GAD signal as an IDSEL in accordance
with the PCI-to-PCI bridge Type 0 configuration mechanism. The remaining address bits are
mapped as described in
Figure 6
.
Figure 6. Configuration Mechanism Type 0 Configuration
Address-to-PCI Address Mapping
Table 5. Configuration Address Decoding
Config Addr AD[15:11]
AGP GAD[31:16] IDSEL
Config Addr AD[15:11]
AGP GAD[31:16] IDSEL
00000
0000 0000 0000 0001
01000
0000 0001 0000 0000
00001
0000 0000 0000 0010
01001
0000 0010 0000 0000
00010
0000 0000 0000 0100
01010
0000 0100 0000 0000
00011
0000 0000 0000 1000
01011
0000 1000 0000 0000
00100
0000 0000 0001 0000
01100
0001 0000 0000 0000
00101
0000 0000 0010 0000
01101
0010 0000 0000 0000
00110
0000 0000 0100 0000
01110
0100 0000 0000 0000
00111
0000 0000 1000 0000
01111
1000 0000 0000 0000
1xxxx
0000 0000 0000 0000
x
x
Register Number
Function #
Device Number
Bus Number
Reserved
1
CONFIG_ADDRESS
31
0
24 23
16 15
11 10
8
7
2
1
0
0
Register Number
Function #
Reserved = 0
IDSEL
31
0
24 23
16 15
11 10
8
7
2
1
14
AGP GAD[31:0] Address