System Address Map
3.10.1
PCI Express* I/O Address Mapping
The GMCH can be programmed to direct non-memory (I/O) accesses to the PCI
Express bus interface when processor initiated I/O cycle addresses are within the PCI
Express I/O address range. This range is controlled via the I/O Base Address
(IOBASE) and I/O Limit Address (IOLIMIT) registers in GMCH Device 1 configuration
space.
Address decoding for this range is based on the following concept. The top 4 bits of
the respective I/O Base and I/O Limit registers correspond to address bits A[15:12] of
an I/O address. For the purpose of address decoding, the GMCH assumes that lower
12 address bits A[11:0] of the I/O base are zero and that address bits A[11:0] of the
I/O limit address are FFFh. This forces the I/O address range alignment to 4 KB
boundary and produces a size granularity of 4 KB.
The GMCH positively decodes I/O accesses to PCI Express I/O address space as
defined by the following equation:
I/O_Base_Address ≤ Processor I/O Cycle Address ≤ I/O_Limit_Address
The effective size of the range is programmed by the plug-and-play configuration
software and it depends on the size of I/O space claimed by the PCI Express device.
The GMCH also forwards accesses to the Legacy VGA I/O ranges according to the
settings in the Device 1 configuration registers BCTRL (VGA Enable) and PCICMD1
(IOAE1), unless a second adapter (monochrome) is present on the DMI Interface/PCI
(or ISA). The presence of a second graphics adapter is determined by the MDAP
configuration bit. When MDAP is set, the GMCH will decode legacy monochrome I/O
ranges and forward them to the DMI Interface. The I/O ranges decoded for the
monochrome adapter are 3B4h, 3B5h, 3B8h, 3B9h, 3BAh, and 3BFh.
Note that the GMCH Device 1 I/O address range registers defined above are used for
all I/O space allocation for any devices requiring such a window on PCI-Express.
The PCICMD1 register can disable the routing of I/O cycles to PCI-Express.
3.11
MCH Decode Rules and Cross-Bridge Address
Mapping
VGAA = 000A_0000h – 000A_FFFFh
MDA = 000B_0000h – 000B_7FFFh
VGAB = 000B_8000h – 000B_FFFFh
MAINMEM = 0100_0000h to TOLUD
HIGHMEM = 4 GB to TOM
RECLAIMMEM = RECLAIMBASE to RECLAIMLIMIT
Datasheet
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INTEL [ INTEL ]
