Intel® 865G/865GV Chipset Datasheet - download.intel.nl - Intel

System Address MapDOS Area (00000h–9FFFFh)The DOS area is 640 KB in size and is always mapped to the main memory controlled by theGMCH.Legacy VGA Ranges (A0000h–BFFFFh)The legacy 128-KB VGA memory range A0000h–BFFFFh (Frame Buffer) can be mapped to IGD(Device 2), to AGP/PCI_B (Device 1), and/or to the hub interface depending on the programmingof the VGA steering bits. Priority for VGA mapping is constant in that the GMCH always decodesinternally mapped devices first. Internal to the GMCH, decode precedence is always given to IGD.The GMCH always positively decodes internally mapped devices, namely the IGD and AGP/PCI_B. Subsequent decoding of regions mapped to AGP/PCI_B or the hub interface depends onthe Legacy VGA configurations bits (VGA Enable and MDAP). This region is also the default forSMM space.Compatible SMRAM Address Range (A0000h–BFFFFh)When compatible SMM space is enabled, SMM-mode processor accesses to this range are routedto physical system SDRAM at this address. Non-SMM-mode processor accesses to this range areconsidered to be to the video buffer area as described above. AGP and HI originated cycles toenabled SMM space are not allowed and are considered to be to the video buffer area.Monochrome Adapter (MDA) Range (B0000h–B7FFFh)Legacy support requires the ability to have a second graphics controller (monochrome) in thesystem. Accesses in the standard VGA range are forwarded to IGD, AGP/PCI_B, and the hubinterface (depending on configuration bits). Since the monochrome adapter may be mapped toanyone of these devices, the GMCH must decode cycles in the MDA range and forward themeither to IGD, AGP/PCI_B, or to the hub interface. This capability is controlled by VGA steeringbits and the legacy configuration bit (MDAP bit). In addition to the memory range B0000h toB7FFFh, the GMCH decodes I/O cycles at 3B4h, 3B5h, 3B8h, 3B9h, 3BAh, and 3BFh andforwards them to the either the IGD, AGP/PCI_B, and/or the hub interface.Expansion Area (C0000h–DFFFFh)This 128-KB ISA Expansion region is divided into eight, 16-KB segments. Each segment can beassigned one of four read/write states: read-only, write-only, read/write, or disabled. Typically,these blocks are mapped through GMCH and are subtractively decoded to ISA space. Memory thatis disabled is not remapped.Extended System BIOS Area (E0000h–EFFFFh)This 64-KB area is divided into four, 16-KB segments. Each segment can be assigned independentread and write attributes so it can be mapped either to main system memory or to hub interface.Typically, this area is used for RAM or ROM. Memory segments that are disabled are notremapped elsewhere.System BIOS Area (F0000h–FFFFFh)This area is a single, 64-KB segment. This segment can be assigned read and write attributes. It isby default (after reset) read/write disabled and cycles are forwarded to the hub interface. Bymanipulating the read/write attributes, the GMCH can “shadow” BIOS into the main systemmemory. When disabled, this segment is not remapped.142 Intel ® 82865G/82865GV GMCH Datasheet