RG82845M Intel, RG82845M Datasheet - Page 75

• Manufacturer Part Number: RG82845M
• Description: Chipset Memory Controller Hub Mobile
• Manufacturer: Intel

3.7.29.
250687-002
R
Address Offset:
APSIZE – Aperture Size – Device #0
Default Value:
Access:
Size:
This register determines the effective size of the Graphics Aperture used for a particular MCH-M
configuration. This register can be updated by the MCH-M specific BIOS configuration sequence before
the PCI standard bus enumeration sequence takes place. If the register is not updated then a 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 and 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.
7:6
5:0
Bit
Reserved
Graphics Aperture Size (APSIZE) (R/W): 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 the corresponding bit of the APBASE[27:22] field 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
Read/Write, Read Only
8 bits
Datasheet
Intel
®
Description
82845MP/82845MZ Chipset-Mobile (MCH-M)
75