AMD-761 Datasheet, PDF (222/264 Pages) Advanced Micro Devices – AMD-761-TM System Controller Software/BIOS Design Guide

Preliminary Information
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Table 34. AGP I/O Settings for 1.5- and 3.3-V Signalling
Register
Dev 0:F0:0xB4
Dev 0:F0:0xB8
Bit/Field Name
FW_Enable
4X_Override
Comp3.3
PCI
Always_Compensate
Do_Compensate
BYP_PDrvXfer
BYP_NDrvXfer
BYPXfer
PSlewXfer
NSlewXfer
BYP_PDrvStrb
BYP_NDrvStrb
BYPStrb
PSlewStrb
NSlewStrb
Bits
[7]
[6]
[5]
[2]
[1]
[0]
[31:28]
[27:24]
[23]
[19:18]
[17:16]
[15:12]
[11:8]
[7]
[3:2]
[1:0]
1.5-V Value
TYPEDET# = 0
1
0
0
0
1
0
Don’t Care
Don’t Care
0
11
11
1111
1111
1
11
11
3.3-V Value
TYPEDET# = 1
0
1
0
0
0
0
Don’t Care
Don’t Care
0
11
11
Don’t Care
Don’t Care
0
11
11
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.
210
AGP Interface
Chapter 6