VT8601 Apollo ProMedia
Revision 1.3 September 8, 1999
-51-
Device 0 Bus 0 Host Bridge Registers
7HFKQRORJLHV ,QF
:H&
:H&RRQQHFW
QQHFW
Device 0 Offset F7-F0 – BIOS Scratch Register .............RW
7-0
No Hardware Function
Device 0 Offset F8 – DRAM Arbitration Timer 1 ..........RW
7-4
AGP Timer (units of 4 DRAM Clocks)
3-0
Host Timer (units of 4 DRAM Clocks)
Device 0 Offset F9 – DRAM Arbitration Timer 2 ..........RW
7-4
VGA High Priority Timer (units of 16 DRAM
Clocks)
3-0
VGA Timer (units of 16 DRAM Clocks)
Device 0 Offset FA – CPU Direct Access Frame Buffer
Base Address A[28:21] ......................................................RW
7-0
A[28:21]
Device 0 Offset FB – Frame Buffer Control ...................RW
7VGA Enable
0
Disable ...................................................default
1Enable
6
VGA Reset ................................. (Write 1 to Reset)
5-4
Frame Buffer Size
00 None
.....................................................default
01 2M
10 4M
11 8M
3
CPU Direct Access Frame Buffer
0
Disable ...................................................default
1Enable
2-0
CPU Direct Access Frame Buffer Base Address
<31:29>
Device 0 Offset FC – Back Door Control 1..................... RW
7-2
Reserved
........................................ always reads 0
1
Back-door MAX # of AGP Request Allowed
0
Read RXA7 will return 7 ....................... default
1
Read RxXA7 will have number programmed at
RxFD
0
Back-Door Device ID Enable
0
Use Rx3-2’s value for Rx3-2 read ......... default
1
Use the value in RxFE-FF
Device 0 Offset FD – Back Door Control 2..................... RW
7-3
Reserved
2-0
Back-Door Max # of AGP Requests the Device can
Handle
000 1-Request ............................................... default
001 2-Requests
……
111 8-Requests
Device 0 Offset FF-FE – Back Door Device ID .............. RW
15-0 Back-Door Device ID................................ default = 0
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