Datasheet

Datasheet 85

3.7.18 FDHC – Fixed DRAM Hole Control Register (Device #0)

Address Offset: 58h

Default Value: 00h

Access: Read/Write

Size: 8 bits

This 8-bit register controls a single fixed DDR SDRAM hole: 15–16 MB.

Bit Description

7 Hole Enable (HEN): This field enables a memory hole in DDR SDRAM space. Host

cycles matching an enabled hole are passed onto ICH4-M through hub interface. The

GMCH/MCH will ignore hub interface cycles matching an enabled hole.

NOTE: A selected hole is not re-mapped.

0 = None

1 = 15 MB–16 MB (1MBs)

6:0 Reserved

3.7.19 PAM(6:0) – Programmable Attribute Map Register (Device

#0)

Address Offset: 59–5Fh

Default Value: 00h Each

Attribute: Read/Write

Size: 4 bits/register, 14 registers

The GMCH allows programmable DDR SDRAM attributes on 13 legacy system memory

segments of various sizes in the 640 kB –1 MB address range. Seven Programmable Attribute

Map (PAM) registers are used to support these features. Cacheability of these areas is controlled

via the MTRR registers in the P6 processor. Two bits are used to specify system memory

attributes for each system memory segment. These bits apply to both Host and hub interface

initiator accesses to the PAM areas. These attributes are:

RE - Read Enable. When RE = 1, the CPU Read accesses to the corresponding system

memory segment are claimed by the GMCH/MCH and directed to main system memory.

Conversely, when RE = 0, the Host Read accesses are directed to PCI0.

WE - Write Enable. When WE = 1, the Host Write accesses to the corresponding system

memory segment are claimed by the GMCH/MCH and directed to main system memory.

Conversely, when WE = 0, the Host Write accesses are directed to PCI0.

The RE and WE attributes permit a system memory segment to be Read Only, Write Only,

Read/Write, or Disabled. For example, if a system memory segment has RE = 1 and WE = 0, the

segment is Read Only.

Each PAM register controls two regions, typically 16 kB in size. Each of these regions has a 4-bit

field. The 4 bits that control each region have the same encoding and are defined in the following

table.