82443BX Datasheet, PDF (88/132 Pages) Intel Corporation – Host Bridge/Controller

Functional Description
4.1.1 Memory Address Ranges
Figure 4-1 provides a detailed 82443BX memory map indicating specific memory regions defined
by AGP and supported by the Intel^® 440BX AGPset.
Figure 4-1. Memory System Address Space
System Memory Space
64 GB
4 GB
Extended CPU
Memory Space
PCI Memory
Window For Non-Prefetchable
PCI accesses to AGP
(Base=MBASE Reg. (20h); Dev 0)
(Size=MLIMIT Reg. (22h); Dev 0)
Graphics Device
Access
(e.g., memory-mapped
control/status registers)
PCI Memory
accesses to AGP
PCI Memory
Window For Prefetchable
PCI accesses to AGP
(Base=PMBASE Reg. (24h); Dev 1)
(Size=PMLIMIT Reg. (26h); Dev 1)
Local Graphics Memory
- Frame Buffer
- Rendering Buffer
- Depth Buffer (Z)
- Video Capture Buffer
PCI Memory
accesses to AGP
PCI Memory
AGP Aperture Range
(Base=APBASE Reg. (10h); Dev 0)
(Size=APSIZE Reg. (B4h); Dev 0)
AGP Aperture
- Textures
- Other Surfaces
- Instruction
Stream
TOM (1 GB Max.)
Graphics Address Re-Mapping Table
(Base=ATTBASE Reg. (B8h); Dev 0)
GART
AGP Data
AGP Data
AGP Data
Optional ISA Hole
AGP
Aperture
PCI Memory
16 MB
15 MB
Main
Memory
0FFFFFh
1 MB
0FFFFFh
1 MB
0F0000h
0EFFFFh
0E0000h
0DFFFFh
Upper BIOS Area
(64 KB)
Lower BIOS Area
(64 KB)
16KBx4
960 KB
896 KB
Expansion Card BIOS
and Buffer Area
(128 KB) 16KBx8
0C0000h
0BFFFFh
768 KB
Standard PCI/ISA Video
Memory (SMM Mem)
128 KB
C0000h
BFFFFh
A0000h
Video BIOS
(shadowed in memory)
Graphics Adapter
(128 KB)
System/Application SW
00000h
DOS
Compatibility
Memory
0A0000h
09FFFFh
080000h
07FFFFh
000000h
Optional Fixed Memory
Hole
DOS Area
(512 KB)
640 KB
512 KB
0 KB
Notes:
1. Graphics Device accesses to the AGP aperture
invoke AGP transfer protocol on the AGP Bus
and use GART to re- map the accesses to
graphics data structures located in main
memory.
2. The two window regions provide PCI accesses
over the AGP.
AGP aperture, GART, and
Graphics data structures mapped by GART
PCI memory accesses to AGP
PCI memory accesses to primary PCI bus
Main memory (physical memory) and
CPU extended memory (above 4 GB)
mem_map2.vsd
4-2
82443BX Host Bridge Datasheet