66
Intel
82865G/82865GV GMCH Datasheet
Register Description
Notes on Pre-Allocated Memory for Graphics
These register bits control the use of memory from main memory space as graphics local memory.
The memory for TSEG is pre-allocated first and then the graphics local memory is pre-allocated.
An example of this theft mechanism is:
TOUD equals 62.5 MB = 03E7FFFFh
TSEG selected as 512 KB in size,
Graphics local memory selected as 1 MB in size
General System RAM available in system = 62.5 MB
General system RAM range00000000h to 03E7FFFFh
TSEG address range03F80000h to 03FFFFFFh
TSEG pre-allocated from03F80000h to 03FFFFFFh
Graphics local memory pre-allocated from03E80000h to 03F7FFFFh
VGA Memory and I/O Space Decode Priority
1. Integrated Graphics Device (IGD), Device 2.
2. PCI-to-PCI bridge, Device 1.
3. Hub Interface.
VGA Memory Space Decode to IGD
IF
IGE = 1 AND IVD = 0 AND Device 2 Mem_Access_En = 1
AND Device 2 in powered up D0 state
AND MSRb1 = 1
AND
→
Additional qualification within IGD decode (comprehends MDA requirements)
ELSE
VGA Mem space legacy decode:
IF
Device 1 Mem_Access_En = 1.
VGA Mem Range
MDA Mem Range
xA0000h – xBFFFFh
xB0000h – xB7FFFh
Mem Access
GR06(3:2)
A0000h–AFFFFh
B0000h–B7FFFh
B8000h–BFFFFh
00
IGD
IGD
IGD
01
IGD
PCI-to-PCI Bridge or
Hub Interface
PCI-to-PCI Bridge or
Hub Interface
10
PCI-to-PCI Bridge or
Hub Interface
IGD
PCI-to-PCI Bridge or
Hub Interface
11
PCI-to-PCI Bridge or
Hub Interface
PCI-to-PCI Bridge or
Hub Interface
IGD
VGA_en
MDAP
Range
Destination
Exceptions/Notes
0
0
VGA, MDA
Hub Interface
0
1
Illegal
Illegal
Illegal
1
0
VGA, MDA
AGP
1
1
VGA, MDA
AGP, Hub Interface