Intel® 945G/945GZ/945GC/ 945P/945PL Express Chipset Family ...

Host Bridge/DRAM Controller Registers (D0:F0)
4.1.18 PAM0—Programmable Attribute Map 0 (D0:F0)
PCI Device: 0
Address Offset: 90h
Default Value: 00h
Access: R/W
Size: 8 bits
This register controls the read, write, and shadowing attributes of the BIOS area from 0F0000h–
0FFFFFh
The (G)MCH allows programmable memory attributes on 13 Legacy memory segments of
various sizes in the 768-KB to 1-MB address range. Seven Programmable Attribute Map (PAM)
registers are used to support these features. Two bits are used to specify memory attributes for
each memory segment. These bits apply to both host accesses and PCI initiator accesses to the
PAM areas. These attributes are:
� RE (Read Enable). When RE = 1, the processor read accesses to the corresponding memory
segment are claimed by the (G)MCH and directed to main memory. Conversely, when
RE = 0, the host read accesses are directed to Primary PCI.
� WE (Write Enable). When WE = 1, the host write accesses to the corresponding memory
segment are claimed by the (G)MCH and directed to main memory. Conversely, when
WE = 0, the host write accesses are directed to Primary PCI.
The RE and WE attributes permit a memory segment to be Read Only, Write Only, Read/Write,
or disabled. For example, if a memory segment has RE = 1 and WE = 0, the segment is Read
Only.
Each PAM Register controls two regions, typically 16 KB in size.
Bit Access &
Default
7:6 Reserved
5:4 R/W
00b
3:0 Reserved
Description
0F0000h–0FFFFFh Attribute (HIENABLE): This field controls the steering of read
and write cycles that addresses the BIOS area from 0F0000 to 0FFFFF.
00 = DRAM Disabled: All accesses are directed to the DMI.
01 = Read Only: All reads are sent to DRAM. All writes are forwarded to the DMI.
10 = Write Only: All writes are sent to DRAM. Reads are serviced by DMI.
11 = Normal DRAM Operation: All reads and writes are serviced by DRAM.
Warning: The (G)MCH may hang if a PCI Express graphics attach or DMI-originated access to read
disabled or write disabled PAM segments occur (due to a possible IWB to non-DRAM). For these
reasons, the following critical restriction is placed on the programming of the PAM regions:
At the time that a DMI or PCI Express graphics attach accesses to the PAM
region may occur, the targeted PAM segment must be programmed to be both
readable and writeable.
76 Intel ® 82945G/82945GZ/82945GC GMCH and 82945P/82945PL MCH Datasheet