Datasheet

System Address Map

Datasheet 165

IGD is not enabled. AGP cycles are allowed to master abort and hub interface writes are

forwarded to AGP; hub interface reads are handled as invalid cycles. If IGD is enabled, all hub

interface accesses are handled as invalid and AGP accesses are handled as invalid cycles.

Monochrome Display Adapter (MDA) Range (0B0000h - 0B7FFFh)

Legacy support requires the ability to have a second graphics controller (monochrome) in the

system. Accesses in the standard VGA range are forwarded to IGD, AGP/PCI1 and the hub

interface (depending on configuration bits). Since the monochrome adapter may be mapped to any

one of these devices, the GMCH/MCH must decode cycles in the MDA range and forward them

either to IGD, AGP/PCI1 or to hub interface. This capability is controlled by VGA steering bits

and the legacy configuration bit (MDAP bit). In addition to the system memory range B0000h to

B7FFFh, the GMCH/MCH decodes IO cycles at 3B4h, 3B5h, 3B8h, 3B9h, 3Bah, and 3BFh and

forwards them to the either the IGD, AGP/PCI1 or the hub interface.

Expansion Area (0C0000h-0DFFFFh)

This 128-kByte ISA Expansion region is divided into eight, 16-kB segments. Each segment can

be assigned one of four Read/Write states: read-only, write-only, read/write, or disabled.

Typically, these blocks are mapped through GMCH/MCH and are subtractively decoded to ISA

space. System memory that is disabled is not re-mapped.

Extended System BIOS Area (0E0000h-0EFFFFh)

This 64-kB area is divided into four, 16-kB segments. Each segment can be assigned independent

read and write attributes so it can be mapped either to main DDR SDRAM or to hub interface.

Typically, this area is used for RAM or ROM. System memory segments that are disabled are not

re-mapped elsewhere.

System BIOS Area (0F0000h-0FFFFFh)

This area is a single 64-kB segment. This segment can be assigned Read and Write attributes. It is

by default (after Reset) Read/Write disabled and cycles are forwarded to hub interface. By

manipulating the Read/Write attributes, the GMCH/MCH can “shadow” BIOS into the main DDR

SDRAM. When disabled, this segment is not re-mapped.

4.3 Extended System Memory Area

This system memory area covers 100000h (1-MB) to FFFFFFFFh (4 GB-1B) address range and it

is divided into the following regions:

• Main system memory from 1-MB to the top of system memory

• AGP or PCI Memory space from the top of system memory to 4-GB with two specific ranges

• APIC Configuration Space from FEC0_0000h (4 GB-20 MB) to FECF_FFFFh (4 GB-19 MB

- 1) and FEE0_0000h (4 GB-18 MB) to FEEF_FFFFh (4 GB-17 MB-1B)

• High BIOS area from 4-GB to 4-GB – 2-MB