Register Description

R

At the time that a hub interface or AGP accesses to the PAM region may occur, the targeted PAM segment must be programmed to be both readable and writeable.

As an example, consider BIOS that is implemented on the expansion bus. During the initialization process, the BIOS can be shadowed in system memory to increase the system performance. When BIOS is shadowed in system memory, it should be copied to the same address location. To shadow the BIOS, the attributes for that address range should be set to write only. BIOS is shadowed by first performing a read of that address. This read is forwarded to the expansion bus. The host then does a write of the same address, which is directed to system memory. After the BIOS is shadowed, the attributes for that memory area are set to read only so that all writes are forwarded to the expansion bus. Table 9 and Figure 2 show the PAM registers and the associated attribute bits:

Figure 2. PAM Register Attributes

PAM6

PAM5

PAM4

PAM3

PAM2

PAM1

PAM0

Offset 96h 95h 94h 93h 92h 91h 90h

7

 

6

 

5

4

3

2

1

0

 

 

R

 

R

 

WE

RE

R

R

WE

 

RE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reserved

 

 

 

 

 

 

 

 

Read Enable (R/W)

Reserved

 

 

 

 

 

 

 

 

1=Enable

Write Enable (R/W)

 

 

 

 

 

 

0=Disable

 

 

 

 

 

Write Enable (R/W)

1=Enable

 

 

 

 

 

 

 

0=Disable

 

 

 

 

 

 

 

1=Enable

Read Enable (R/W)

 

 

 

 

0=Disable

 

 

 

Reserved

1=Enable

 

 

 

 

 

 

 

 

 

 

 

Reserved

 

 

 

0=Disable

 

 

 

 

 

 

pam

60

Intel® 82845 MCH for SDR Datasheet

Page 60
Image 60
Intel 845 manual PAM Register Attributes, PAM6 PAM5 PAM4 PAM3 PAM2 PAM1 PAM0