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Recommended BIOS Settings
Chapter 7
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Preliminary Information
7.1.1
Example Settings for Memory Timing
The table below provides example BIOS settings for the DRAM
Timing register, for both 100-MHz and 133-MHz bus speeds.
Note some register bits change based on the DIMM type:
U
for Unbuffered DIMMs
R
for registered DIMMs
Note also that SPD values observed to date are from production
DIMMs. Future additions and changes to the SPD bytes should
be expected.
Registers
-----
Bits
Description
Initialized/
Required
Value
Actual
Value
Key
fcn( )
Notes
0x0x0x54h
SDRAM Timing
6:4
t
RAS
= Minimum Bank Active
Time
SPD # 30
xxxb
B
FSB
and
SPD
000 = 2 cyc, 001 = 3 cyc
010 = 4 cyc, 011 = 5 cyc
100 = 6 cyc
101 = 7 cyc (safe)
110 = 8 cyc, 111 = 9 cyc
3:2
t
CL
= CAS Latency
SPD # 25 or
# 23 or
# 9
xxb
B
FSB
and
SPD
00 = 3 cyc (optional on
DIMM,
not
recommended)
01 = 2 cyc, recommended
10 = 2.5 cyc, 11-reserved
1:0
t
RCD
— RAS to CAS Latency
SPD # 29
xxb
B
FSB
and
SPD
00 = 1 cyc, 01 = 2 cyc
10 = 3 cyc (safe), 11 = 4 cyc
KEY:
B= Mandatory BIOS function
A= AGP setup by BIOS
c = Calculated/set by AMD-761™ internal logic
P= Power management setup by BIOS
o = Setup by OS or OS driver
F = Performance enhancement set by BIOS
r = Hardcoded and reserved
u = PCI operational user interface
E = Elective BIOS function