
PRELIMINARY
49
A
82454KX/GX (PB)
2.4.30 IOSR1—I/O SPACE RANGE 1 REGISTER (82454GX ONLY)
2.4.31 PCIRSR—PCI RESET REGISTER
Address Offset:
9Ch
Default:
00h
Attribute:
Read/Write
This register permits software to reset the PCI bus without also resetting the CPU bus. Note, the PCI bus is
always reset when the host bus is reset through a hard or power-on reset.
Bits
Description
31:20
I/O Space Range 1 End Address. Bits [31:20] correspond to A[15:4]. Must be set to the same
value in both bridges.
19:16
Reserved.
15:4
I/O Space Range 1 Start Address. Bits [15:4] correspond to A[15:4]. Must be set to the same
value in both bridges.
3:1
Reserved.
0
I/O Space Range 1 Enable. 1=Forward host bus accesses in the range to PCI and ignore PCI bus
accesses in the range. 0=Ignore host bus accesses in the range and forward PCI bus accesses in
the range to the host bus.
Compatibility bridge: 1=default. To open a gap in the compatibility bridge I/O space, this bit must set
to 0.
Auxiliary bridge: 0=default. To claim an I/O range in the auxiliary bridge, this bit must be set to 1.
Bits
Description
7:1
Reserved.
0
Reset PCI Bus. Setting this bit from 0 to 1 causes the PB to assert PCIRST# for at least one milli-
second. Resetting the PCI bus could cause unwanted system signals to drive into the processor. Be
sure to understand the state of any signals going from the PCI bus back to the processor during
reset. See Section 3.7.5.
Address Offset:
98–9Bh
Default:
FFF0 0001h (Compatibility PB)
FFF0 0000h (Auxiliary PB)
Attribute:
Read/Write
This register defines an I/O space range. A second I/O space range is defined by the IOSR2 Register. Except
for the ranges defined by these two registers, the Compatibility PB forwards all host bus accesses to PCI
(and ignores PCI bus accesses) and the Auxiliary PB ignores all host bus accesses (and forwards PCI bus
accesses to the host bus).