AMD-761 Datasheet, PDF (97/264 Pages) Advanced Micro Devices – AMD-761-TM System Controller Software/BIOS Design Guide

24081D—February 2002
Preliminary Information
AMD-761™ System Controller Software/BIOS Design Guide
Bit Definitions
Bit Name
31–17 Reserved
16 Vga_IA_En
15–4 Reserved
3–1 VA_Size
0 GART_En
Programming Notes
AGP Virtual Address Space Size (Dev0:F0:0xAC)
Function
Reserved
ISA Address Aliasing Enable
When set, this bit forces the AMD-761™ system controller to alias ISA addresses, which
means that address bits [15:10] are not used in decoding. When clear, no ISA aliasing is
performed and address bits [15:10] are used for decoding.
Reserved
Virtual Address Size
This field defines the virtual address space size to be allocated to GART by the system
BIOS. Prior to the execution of the system BIOS memory mapping software, system BIOS
gets the amount of GART virtual address space required by the graphics controller. It sets
these bits to the required value. Changing these bits automatically changes bits [30:25] in
the host-PCI bridge (device 0) AGP Virtual Address Space register, offset 0x10 (see
“Dev0:F0:0x10” on page 37).
The size of GART virtual address space is always greater than or equal to the amount of
physical system memory allocated to AGP in non-contiguous 4-Kbyte blocks. The amount
of physical memory allocated to AGP is determined by operating system software.
[3] [2] [1] VA_Size
0
0 0 32 Mbytes
0
0 1 64 Mbytes
0
1 0 128 Mbytes
0
1 1 256 Mbytes
1
0 0 512 Mbytes
1
0 1 1 Gbytes
1
1 0 2 Gbytes
GART Enable
When clear, GART is not valid in this system. System BIOS does not allocate virtual address
space for GART because the host-PCI bridge (device 0) AGP virtual address space, offset
0x10 (see “Dev0:F0:0x10” on page 37) is set to 0. The PCI-PCI bridge (device 1) capabilities
pointer is set to point to the next item in the linked list or null if there is no other item. This
bit is set by BIOS PCI enumeration routines.
When set, GART is valid in this system. System BIOS allocates virtual address space for
GART based upon the value in bits [3:1] above.
Chapter 2
AMD-761™ System Controller Programmer’s Interface
85