
50
PRELIMINARY
82454KX/GX (PB)
A
2.4.32 IOSR2—I/O SPACE RANGE 2 REGISTER (82454GX ONLY)
.
2.4.33 APICR—I/O APIC RANGE REGISTER
Address Offset:
A4–A7h
Default:
00FE C001h (82454KX)
Attribute:
Read/Write
This range defines an I/O APIC range. There can be up to 16 APICs, with contiguous ascending unit IDs below
a PB. One of the 16 APIC 4 Kbyte blocks must be reserved for all CPU Local APIC units. (Multiple CPU(s) may
use the same Local APIC address since Local APIC transactions are not visible on the host bus.) The PB
responds to I/O APIC address range (base + x000h) through (base + yFFFh) where x is the I/O APIC Starting
Unit ID and y is the highest unit ID number.
Note that a 64 Kbyte range is allocated to APIC space. Local APIC transactions are not visible on the host bus,
but still require UC MTRR attributes. The Local APIC base address register in each processor should be
programmed to point to one of the 4 Kbyte blocks in the 64 Kbyte APIC range so that one MTRR may be used
for Local and I/O APIC configuration ranges. The MC does not reclaim any 64 Kbyte memory gaps created for
the APIC range.
Bits
Description
31:20
I/O Space Range 2 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 2 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 Range 2 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.
Address Offset:
A0–A3h
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 IOSR1 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)
00FE C001h (Compatibility PB)
00FE C000h (Auxiliary PB)
If there is an I/O APIC behind more than one PB, each PB must use the same APIC base address and all
64KB of APIC range must be accounted for among the PBs.