JG82855GMESL7VN Datasheet, PDF(126/213 Page) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

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JG82855GMESL7VN Datasheet, PDF (126/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

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IntelÂ® 855GM/GME GMCH System Address Map

Table 32. System Memory Segments and Their Attributes

System Memory

Segments

000000H - 09FFFFH

0A0000H - 0BFFFFH

0C0000H - 0C3FFFH

0C4000H - 0C7FFFH

0C8000H - 0CBFFFH

0CC000H - 0CFFFFH

0D0000H - 0D3FFFH

0D4000H - 0D7FFFH

0D8000H - 0DBFFFH

0DC000H - 0DFFFFH

0E0000H - 0E3FFFH

0E4000H - 0E7FFFH

0E8000H - 0EBFFFH

0EC000H - 0EFFFFH

0F0000H - 0FFFFFH

Attributes

Comments

Fixed - always mapped to main

DDR SDRAM

Mapped to Hub interface or IGD -

configurable as SMM space

WE(Write Enable) RE (Read

Enable)

WE RE

0 to 640 kB â DOS Region

Video Buffer (physical DDR SDRAM

configurable as SMM space)

Add-on BIOS

BIOS Extension

BIOS Area

DOS Area (000000h-09FFFFh)

The DOS area is 640-kB in size and is always mapped to the main system memory controlled by

the GMCH.

Legacy VGA Ranges (0A0000h-0BFFFFh)

The legacy 128-kB VGA memory range A0000h-BFFFFh (VGA Frame Buffer) can be mapped to

IGD (Device #2) and to the Hub interface depending on the programming of the VGA steering

bits. Priority for VGA mapping is constant in that the GMCH always decodes internally 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. Subsequent decoding of

regions mapped to the Hub interface depends on the Legacy VGA configurations bits (VGA

Enable and MDAP). This region is also the default for SMM space.

Compatible SMRAM Address Range (0A0000h-0BFFFFh)

When compatible SMM space is enabled, SMM-mode CPU accesses to this range are routed to

physical DDR SDRAM at this address. Non-SMM-mode CPU accesses to this range are

considered to be to the video buffer area as described above. Hub interface originated cycles to

enabled SMM space are not allowed and are considered to be to the video buffer area.

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Datasheet

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