AC82G41SLGQ3 Datasheet, PDF (58/604 Pages) Intel Corporation – Intel® 4 Series Chipset Family

System Address Map
decoding of regions mapped to PCI Express or the DMI Interface depends on the
Legacy VGA configuration bits (VGA Enable and MDAP). This region is also the default
for SMM space.
Compatible SMRAM Address Range (A_0000h–B_FFFFh)
When compatible SMM space is enabled, SMM-mode processor accesses to this range
are routed to physical system DRAM at 000A 0000h – 000B FFFFh. Non-SMM-mode
processor accesses to this range are considered to be to the Video Buffer Area as
described above. PCI Express and DMI originated cycles to enabled SMM space are not
allowed and are considered to be to the Video Buffer Area if IGD is not enabled as the
VGA device. PCI Express and DMI initiated cycles are attempted as Peer cycles, and will
master abort on PCI if no external VGA device claims them.
Monochrome Adapter (MDA) Range (B_0000h–B_7FFFh)
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, PCI Express,
or the DMI Interface (depending on configuration bits). Since the monochrome adapter
may be mapped to anyone of these devices, the (G)MCH must decode cycles in the
MDA range (000B_0000h – 000B_7FFFh) and forward either to IGD, PCI Express, or
the DMI Interface. This capability is controlled by a VGA steering bits and the legacy
configuration bit (MDAP bit). In addition to the memory range B0000h to B7FFFh, the
(G)MCH decodes I/O cycles at 3B4h, 3B5h, 3B8h, 3B9h, 3BAh and 3BFh and forwards
them to the either IGD, PCI Express, and/or the DMI Interface.
PEG 16-bit VGA Decode
The PCI to PCI Bridge Architecture Specification, Revision 1.2, states that 16-bit VGA
decode be a feature.
It is expected that once the official version of the PCI to PCI Bridge Architecture
Specification, Revision 1.2, has been released that Microsoft will include a Windows
Logo program requirement that devices are compliant to this version of specification. A
draft version of the Windows Logo Program 3.0 document includes this requirement as
a proposed requirement; also Microsoft may potentially make this an out of band
update to the existing WLP2.1a requirements.
The VGA 16-bit decode originally was described in an ECR to the PCI to PCI Bridge
Architecture Specification, Revision 1.1, this is now listed as a required feature in the
updated 1.2 specification.
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Datasheet