
82815 GMCH
R
Datasheet
77
3.4.32.
APSIZE—Aperture Size (Device 0: AGP Mode Only)
Address Offset:
B4h
Default Value:
00h
Access:
Read/Write
Size:
8 bits
This register determines the effective size of the graphics aperture used for a particular GMCH
configuration. This register can be updated by the GMCH-specific BIOS configuration sequence before
the PCI standard bus enumeration sequence takes place. If the register is not updated, a default value will
select an aperture of maximum size (i.e., 64 MB).
7
4
3
2
0
Reserved
GFX
Aperture
Size
Reserved
Bit
Description
7:4
Reserved.
3
Graphics Aperture Size (GASIZE).
Bit 3 operates on bit 25 of the Aperture Base (APBASE)
configuration register. When this bit is 0, it forces bit 25 in APBASE to behave as “hardwired” to 0.
When this bit is 1, it forces bit 25 in APBASE to be read/write accessible. Only the following
combinations are allowed:
0 = 64 MB Aperture Size
1 = 32 MB Aperture Size
Default for APSIZE[3]=0b forces default APBASE[25] =0b (responds as “hardwired” to 0). This provides
maximum aperture size of 64 MB. Programming APSIZE[3]=1b enables APBASE[25] as read/write
programmable.
2:0
Reserved.