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AMD-761™ System Controller Programmer’s Interface
Chapter 2
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Preliminary Information
Programming Notes
When transitioning from bypass enabled to disabled via the AGP Compensation Bypass register (Dev 0:F0:0xB8), the
Do_Compensate bit should be set. AGP should not be subsequently enabled until the Do_Compensate bit is read back as
a 0, indicating that the compensation cycle is complete.
Refer to the AGP Compensation Bypass register (Dev 0:F0:0xB8) for details of bypass mode.
1
Always_
Compensate
Always Compensate
When set, dynamic compensation is performed by AGP on an ongoing basis at
regular intervals.
0
Do_Compensate
Do Compensate
This bit is used to initiate a dynamic compensation command on AGP. This bit is cleared by
the AMD-761™ system controller when the compensation cycle is complete. See the
programming note below on recommendation for exiting bypass mode.
Table 9.
I/O Pad Drive Strength and Input Type
BYPASS
TYPEDET#
PCI
AGP Mode
Output Drive Strength
0
0
X
N/A
Compensated Strength
0
1
0
N/A
AGP-1X Strength
0
1
1
N/A
PCI Strength
1
X
X
N/A
Bypass, User Configurable
BYPASS
TYPEDET#
PCI
AGP Mode
Input Type
X
0
X
4X
Differential
X
0
X
1X/2X
Single-Ended
X
1
X
1X/2X
Single-Ended
X
1
X
1X/2X
Single-Ended
Bit Definitions (Continued)
AGP 4X Dynamic Compensation (Dev0:F0:0xB4)
Bit
Name
Function