210
AGP Interface
Chapter 6
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Preliminary Information
6.4
AGP Miniport Driver Requirements
AMD has found that some early generation 4x AGP cards were
not consistently implemented using published 4x AGP
guidelines for AGP signal impedance and routing. These AGP
cards do not work reliably with the default AGP drive-strengths
of the AMD-761 system controller. As a result, AMD has
developed a mini-port solution to adjust the AMD-761 system
controller AGP drive strengths to the optimal levels for these
early generation AGP cards as identified by the vendor and
device ID in PCI configuration space. AMD does not plan for
any current or future generation AGP cards to experience any
incompatibilities with the AMD-761 system controller. If a card
is identified that requires a drive strength change, the AMD
mini-port or the AGP card is updated to allow compatibility.
Table 34.
AGP I/O Settings for 1.5- and 3.3-V Signalling
Register
Bit/Field Name
Bits
1.5-V Value
TYPEDET# = 0
3.3-V Value
TYPEDET# = 1
Dev 0:F0:0xB4
FW_Enable
[7]
1
0
4X_Override
[6]
0
1
Comp3.3
[5]
0
0
PCI
[2]
0
0
Always_Compensate
[1]
1
0
Do_Compensate
[0]
0
0
Dev 0:F0:0xB8
BYP_PDrvXfer
[31:28]
Don’t Care
Don’t Care
BYP_NDrvXfer
[27:24]
Don’t Care
Don’t Care
BYPXfer
[23]
0
0
PSlewXfer
[19:18]
11
11
NSlewXfer
[17:16]
11
11
BYP_PDrvStrb
[15:12]
1111
Don’t Care
BYP_NDrvStrb
[11:8]
1111
Don’t Care
BYPStrb
[7]
1
0
PSlewStrb
[3:2]
11
11
NSlewStrb
[1:0]
11
11