Datasheet

Datasheet 83

3.7.16 GGC – GMCH Graphics Control Register (Device 0)

Address Offset: 52–53h

Default Value: 0030h

Access: Read/Write

Size: 16 bits

Bit Description

15:7 Reserved

6:4 Graphics Mode Select (GMS): This field is used to select the amount of main system memory

that is pre-allocated to support the Internal Graphics Device in VGA (non-linear) and Native

(linear) modes. The BIOS ensures that system memory is pre-allocated only when Internal

Graphics is enabled.

000 = No system memory pre-allocated. Device #2 (IGD) does not claim VGA cycles (Memory

and I/O), and the Sub-Class Code field within Device #2 Function #0 Class Code register

is 80.

001 = DVMT (UMA) mode, 1 MB of system memory pre-allocated for frame buffer.

010 = DVMT (UMA) mode, 4 MB of system memory pre-allocated for frame buffer.

011 = DVMT (UMA) mode, 8 MB of system memory pre-allocated for frame buffer.

100 = DVMT (UMA) mode, 16 MB of system memory pre-allocated for frame buffer.

101 = DVMT (UMA) mode, 32 MB of system memory pre-allocated for frame buffer.

All other combinations reserved.

3:2 Reserved

1 IGD VGA Disable (IVD):

1 = Disable. Device #2 (IGD) does not claim VGA Memory and I/O Mem cycles, and the Sub-

Class Code field within Device #2 Function #0 Class Code register is 80.

0 = Enable. Device #2 (IGD) claims VGA Memory and I/O cycles, the Sub-Class Code within

Device #2 Class Code register is 00.

0 Reserved