
12
PRELIMINARY
PCIset Overview
A
I/O APIC units (there should be at least one for each I/O subsystem) are located beginning at the default base
address FEC00000h. The first I/O APIC (unit #0) is at FEC00000h. Each I/O APIC unit is located at
FEC0x000h where x is I/O APIC unit 0 through F.
The address range between the APIC Configuration space and the High BIOS (FED00000h–FFDFFFFFh) is
always mapped to local memory unless the range is above top of physical memory or The High BIOS and APIC
Range are disabled in the PB and the range falls within a memory gap range. The MC supports enabling or
disabling this region for access to the MC memory via the I/O APIC Range Register.
4.4
Extended Memory (above 4 Gbytes)
The Extended Memory region is from 4 Gbyte to 64 Gbyte (100000000h–FFFFFFFFFh). The PB and MC can
be mapped into this range. The Memory Gap Range and High Memory Gap Range are both available for use
within the Extended memory region (above 4 Gbyte).
4.5
System Management Mode (SMM)
A Pentium Pro processor asserts SMMEM# in its Request Phase if it is operating in System Management
Mode. SM code resides in SM memory space. SM memory can overlap with memory residing on the Pentium
Pro processor bus or memory normally residing on the PCI bus. The MC and PB determine where SM memory
space is located through the value programmed in their respective SMM Range Registers.
5.0
I/O SPACE (PB ONLY)
The PB optionally supports ISA expansion aliasing (Figure 6). When ISA expansion aliasing is enabled, the
ranges designated as I/O Expansion are internally aliased to the 100–3FFh range before the I/O Space Range
registers are checked. Note that all devices on the Pentium Pro processor bus that are mapped into I/O space
must have I/O aliasing consistently enabled/disabled.
For the Intel 450GX PCIset, the PB allows I/O addresses to be mapped to the Pentium Pro processor bus or
through designated bridges in a multi bridge system. Two I/O Space Range registers allow the PB to decode
two I/O address ranges. If the address range is enabled, transactions targeting that range are forwarded to the
PCI bus. If the address range is disabled, the transaction is ignored.