Revision 3.1
101
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Integrated Functions (
Continued
)
G
4.2.5
The Internal Bus Interface Unit maps 100h locations start-
ing at GX_BASE+8000h. Refer to Section 4.1.2 “Control
Registers” on page 94 for instructions on accessing these
registers.
Internal Bus Interface Unit Registers
Table 4-9 summarizes the four 32-bit registers contained
in the Internal Bus Interface Unit and Table 4-10 gives the
register/bit formats.
Table 4-9. Internal Bus Interface Unit Register Summary
GX_BASE+
Memory Offset
Type
Name/Function
Default
Value
8000h-8003h
R/W
BC_DRAM_TOP
Top of DRAM: Contains the highest available address of system memory not
including the memory that is set aside for graphics memory, which corresponds to
1 GByte of memory. The largest possible value for the register is 3FFFFFFFh.
BC_XMAP_1
Memory X-Bus Map Register 1 (A and B Region Control: Contains the region
control of the A and B regions and the SMI controls required for VGA emulation.
PCI access to internal registers and the A20M function are also controlled by this
register.
BC_XMAP_2
Memory X-Bus Map Register 2 (C and D Region Control): Contains region con-
trol fields for eight regions in the address range C0h through DCh.
BC_XMAP_3
Memory X-Bus Map Register 3 (E and F Region Control): Contains the region
control fields for memory regions in the address range E0h through FCh.
3FFFFFFFh
8004h-8007h
R/W
00000000h
8008h-800Bh
R/W
00000000h
800Ch-800Fh
R/W
00000000h
Table 4-10. Internal Bus Interface Unit Registers
Bit
Name
Description
GX_BASE+8000h-8003h
BC_DRAM_TOP Register (R/W)
Default Value = 3FFFFFFFh
31:30
29:17
RSVD
TOP OF
DRAM
1FFFF
Reserved:
Set to 0.
Top of DRAM:
Maximum value is FFFh.
16:0
Granularity:
Must be set to 1FFFFh (128 KB).
GX_BASE+8004h-8007h
BC_XMAP_1 Register (R/W)
Default Value = 00000000h
31:29
28
RSVD
GEB8
Reserved:
Set to 0.
Graphics Enable for B8 Region:
Allow memory R/W operations for address range B8000h-BFFFFh be
directed to the graphics pipeline: 0 = Disable; 1 = Enable.
(Used for VGA emulation.)
B8 Region:
Region control field for address range B8000h-BFFFFh.
Note:
Refer to Table 4-11 for decode.
Reserved:
Set to 0.
PCI Register Access Enable:
Allow PCI Slave to access internal registers on the X-Bus:
0 = Disable; 1 = Enable.
Address Bit 20 Mask:
Address bit 20 is always forced to a zero except for SMI accesses:
0 = Disable; 1 = Enable.
Graphics Enable for B0 Region:
Allow memory R/W operations for address range B0000h-B7FFFh be
directed to the graphics pipeline: 0 = Disable; 1 = Enable.
(Used for VGA emulation.)
B0 Region:
Region control field for address range B0000h-B7FFFh.
Note:
Refer to Table 4-11 for decode.
SMID:
All I/O accesses for address range 3D0h-3DFh generate an SMI: 0 = Disable; 1 = Enable.
(Used for VGA virtualization.)
SMIC:
All I/O accesses for address range 3C0h-3CFh generate an SMI: 0 = Disable; 1 = Enable.
(Used for VGA virtualization.)
SMIB:
All I/O accesses for address range 3B0h-3BFh generate an SMI: 0 = Disable; 1 = Enable
(Used for VGA virtualization.)
27:24
B8
23
22
RSVD
PRAE
21
A20M
20
GEB0
19:16
B0
15
SMID
14
SMIC
13
SMIB