Intel D15343-003 - Manual (Page 41)

Register Description
D15343-003 41
4.0 Register Description
4.1 Conceptual Overview of the Platform Configuration
Structure
The GMCH and ICH4-M are physically connected by a Hub interface. From a configuration
standpoint, the Hub interface is logically PCI bus #0. As a result, all devices internal to the GMCH
and ICH4-M appear to be on PCI bus #0. The system's primary PCI expansion bus is physically
attached to the ICH4-M and from a configuration perspective, appears to be a hierarchical PCI bus
behind a PCI-to-PCI bridge and therefore has a programmable PCI Bus number. Note that the
primary PCI bus is referred to as PCI_A in this document and is not PCI bus #0 from a
configuration standpoint. For the GMCH, the graphics subsystem appears to system software to be
a real PCI bus behind PCI-to-PCI bridges, resident as devices on PCI bus #0.
The GMCH contains two PCI devices within a single physical component. The configuration
registers for the two devices are mapped as devices residing on PCI bus #0.
Device #0: Host-Hub Interface Bridge/DDR SDRAM Controller. Logically this appears as a PCI
device residing on PCI bus #0. Physically, Device #0 contains the standard PCI registers, DDR
SDRAM registers, the Graphics Aperture Controller registers, HI Control registers and other
GMCH specific registers. Device #0 is divided into the following functions:
Function #0: Host Bridge Legacy registers including Graphics Aperture Control registers, HI
Configuration registers and Interrupt Control registers
Function #1: DDR SDRAM Interface Registers
Function #3: Intel Configuration Process Registers
Device #2: Integrated Graphics Controller. Logically this appears as a PCI device residing on PCI
bus #0. Physically Device #2 contains the Configuration registers for 2D, 3D, and display
functions.
Note: The legacy VGA registers are only supported when the Intel
®
82854 GMCH is strapped into
Native Graphics Mode.
Table 15 shows the Device # assignment for the various internal GMCH devices.
Table 15. Device Number Assignment
GMCH Function Bus #0, Device#
Host-Hub interface, DDR SDRAM I/F, Legacy control Device #0
Integrated Graphics Controller (IGD) Device #2