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82854 Graphics Memory Controller Hub (GMCH)
78 D15343-003
4.9.11 CAPPTR – Capabilities Pointer Register
The CAPPTR provides the offset that is the pointer to the location of the first device capability in
the capability list.
4.9.12 DRB – DRAM Row (0:3) Boundary Register (Device #0)
The DDR SDRAM Row Boundary Register defines the upper boundary address of each DDR
SDRAM row with a granularity of 32 MB. Each row has its own single-byte DRB register. For
example, a value of 1 in DRB0 indicates that 32 MB of DDR SDRAM has been populated in the
first row. Since the GMCH supports a total of four rows of system memory, DRB0-3 are used. The
registers from 44h-4Fh are Reserved for DRBs 4-15.
Row0: 40h
Row1: 41h
Row2: 42h
Row3: 43h
44h to 4Fh is reserved.
DRB0 = Total system memory in Row0 (in 32-MB increments)
DRB1 = Total system memory in Row0 + Row1 (in 32-MB increments)
DRB2 = Total system memory in Row0 + Row1 + Row2 (in 32-MB increments)
DRB3 = Total system memory in Row0 + Row1 + Row2 + Row3 (in 32-MB increments)
Each Row is represented by a Byte. Each Byte has the following format.
Address Offset:
Default Value:
Access:
Size:
34h
00h
Read Only
8 bits
Bit Descriptions
7:0 Pointer to the offset of the first capability ID register block: In this case there are no
capabilities, therefore these bits are hardwired to 00h to indicate the end of the capability linked
list.
Address Offset:
Default Value:
Access:
Size:
40-43h
00h each
Read/Write
8 bits each
Bit Descriptions
7:0 DDR SDRAM Row Boundary Address: This 8-bit value defines the upper and lower addresses
for each DDR SDRAM row. This 8-bit value is compared against a set of address lines to
determine the upper address limit of a particular row. Also the minimum system memory
supported is 64 MB in 64-Mb granularity; hence bit 0 of this register must be programmed to a
zero.