AMD-761 Datasheet, PDF (166/264 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
Note: Modes 00b and 11b are reserved.
To determine the size of the DDR SDRAM device from SPD
data, BIOS needs to read the size of the bank(s) in SPD byte 31
and the device width in byte 13. DDR SDRAM widths are
either 4, 8, or 16 for this implementation. A 4-bit device width
implies that 16 DDR SDRAM devices exist on a DIMM for a
64-bit bus transfer. An 8-bit device width implies eight DDR
SDRAM devices exist on a DIMM for a 64-bit bus transfer, and
a 16-bit width implies four DDR SDRAM devices exist on a
DIMM for the 64-bit bus transfer. The size of the bank can be
deduced as:
Size of Device(Mbits) = Size of Bank x (SDRAM Width)
where the Size of Device is specified in Mbits. Dividing the
Size of Device value by eight (8) yields the size of the bank in
Mbytes.
If more than 4 Gbytes of total memory are populated in the
system, it is the responsibility of BIOS to configure and report
only 4 Gbytes to prevent a 4-Gbyte wrap, which would result in
aliasing. Table 20 shows the total amount of memory with
respect to DDR device density and width.
Table 20. Total Memory
Width and
Density
X16 128 Mbit
X8 128 Mbit
X4 128 Mbit
X16 256 Mbit
X8 256 Mbit
X4 256 Mbit
X16 512 Mbit
X8 512 Mbit
X4 512 Mbit
DIMM 0
128 Mbytes
256 Mbytes
512 Mbytes
256 Mbytes
512 Mbytes
1 Gbyte
512 Mbytes
1 Gbyte
2 Gbytes
DIMM 1
256 Mbytes
512 Mbytes
1 Gbytes
512 Mbytes
1 Gbytes
2 Gbytes
1 Gbytes
2 Gbytes
4 Gbytes
DIMM 2
384 Mbytes
768 Mbytes
1.5 Gbytes
768 Mbytes
1 Gbytes
3 Gbytes
1.5 Gbytes
3 Gbytes
DIMM 3
512 Mbytes
1 Gbytes
2 Gbytes
1 Gbytes
2 Gbytes
4 Gbytes
2 Gbytes
4 Gbytes
Note: This table assumes double sided DIMMs.
Note: Total system maximum is 4 Gbytes.
Note: Shaded rows use x4 devices that are as registered DIMMs only.
154
DDR SDRAM Interface
Chapter 3