RG82845 S L5YQ Intel, RG82845 S L5YQ Datasheet - Page 69

• Manufacturer Part Number: RG82845 S L5YQ
• Manufacturer: Intel

Specifications of RG82845 S L5YQ

• Lead Free Status / RoHS Status: Not Compliant

3.5.29
Intel
®
82845 MCH for SDR Datasheet
R
APSIZE—Aperture Size (Device 0)
Address Offset:
Default Value:
Access:
Size:
This register determines the effective size of the Graphics Aperture used for a particular MCH
configuration. This register can be updated by the MCH specific BIOS configuration sequence
before the PCI standard bus enumeration sequence takes place. If the register is not updated, the
default value will select an aperture of maximum size (i.e., 256 MB). The size of the table that will
correspond to a 256 MB aperture is not practical for most applications; therefore, these bits must
be programmed to a smaller practical value that will force adequate address range to be requested
via APBASE register from the PCI configuration software.
Bit
7:6
5:0
Reserved.
Graphics Aperture Size (APSIZE). Each bit in APSIZE[5:0] operates on similarly ordered bits in
APBASE[27:22] of the Aperture Base configuration register. When a particular bit of this field is 0,
it forces the similarly ordered bit in APBASE[27:22] to behave as “hardwired” to 0. When a
particular bit of this field is set to 1, it allows corresponding bit of the APBASE[27:22] to be
read/write accessible. Only the following combinations are allowed:
5 4 3 2 1 0
1 1 1 1 1 1
1 1 1 1 1 0
1 1 1 1 0 0
1 1 1 0 0 0
1 1 0 0 0 0
1 0 0 0 0 0
0 0 0 0 0 0
Default for APSIZE[5:0]=000000b forces default APBASE[27:22] =000000b (i.e., all bits respond
as “hardwired” to 0). This provides maximum aperture size of 256 MB. As another example,
programming APSIZE[5:0]=111000b hardwires APBASE[24:22]=000b and while enabling
APBASE[27:25] as read/write.
Aperture Size
4 MB
8 MB
16 MB
32 MB
64 MB
128 MB
256 MB
B4h
00h
R/W
8 bits
Description
Register Description
69