70
Intel
82865G/82865GV GMCH Datasheet
Register Description
As an example, consider BIOS that is implemented on the expansion bus. During the initialization
process, BIOS can be shadowed in main memory to increase the system performance. When BIOS
is shadowed in main memory, it should be copied to the same address location. To shadow BIOS,
the attributes for that address range should be set to write only. The BIOS is shadowed by first
doing a read of that address. This read is forwarded to the expansion bus. The host then does a
write of the same address that is directed to main 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.
Figure 8
and
Table 7
show the PAM registers and the associated attribute bits.
Figure 8. PAM Register Attributes
Table 7. PAM Register Attributes
PAM Reg
Attribute Bits
Memory Segment
Comments
Offset
PAM0[3:0]
Reserved
90h
PAM0[7:6]
Reserved
90h
PAM0[5:4]
R
R
WE
RE
0F0000h–0FFFFFh
BIOS Area
90h
PAM1[1:0]
R
R
WE
RE
0C0000h–0C3FFFh
ISA Add-on BIOS
91h
PAM1[7:4]
R
R
WE
RE
0C4000h–0C7FFFh
ISA Add-on BIOS
91h
PAM2[1:0]
R
R
WE
RE
0C8000h–0CBFFFh
ISA Add-on BIOS
92h
PAM2[7:4]
R
R
WE
RE
0CC000h–0CFFFFh
ISA Add-on BIOS
92h
PAM3[1:0]
R
R
WE
RE
0D0000h–0D3FFFh
ISA Add-on BIOS
93h
PAM3[7:4]
R
R
WE
RE
0D4000h–0D7FFFh
ISA Add-on BIOS
93h
PAM4[1:0]
R
R
WE
RE
0D8000h–0DBFFFh
ISA Add-on BIOS
94h
PAM4[7:4]
R
R
WE
RE
0DC000h–0DFFFFh
ISA Add-on BIOS
94h
PAM5[1:0]
R
R
WE
RE
0E0000h–0E3FFFh
BIOS Extension
95h
PAM5[7:4]
R
R
WE
RE
0E4000h–0E7FFFh
BIOS Extension
95h
PAM6[1:0]
R
R
WE
RE
0E8000h–0EBFFFh
BIOS Extension
96h
PAM6[7:4]
R
R
WE
RE
0EC000h–0EFFFFh
BIOS Extension
96h
RE
WE
RE
R
R
WE
R
R
7
6
5
4
3
2
1
0
PAM6
PAM5
PAM4
PAM3
PAM2
PAM1
PAM0
Read Enable (R/W)
1=Enable
0=Disable
Write Enable (R/W)
1=Enable
0=Disable
Reserved
Reserved
Read Enable (R/W)
1=Enable
0=Disable
Write Enable (R/W)
1=Enable
0=Disable
Reserved
Reserved
96h
95h
94h
93h
92h
91h
90h
Offset