System Support

APIC Mode

The Advanced Programmable Interrupt Controller (APIC) mode provides enhanced interrupt processing with the following advantages:

■Eliminates the processor's interrupt acknowledge cycle by using a separate (APIC) bus

■Programmable interrupt priority

■Additional interrupts (total of 24)

The APIC mode accommodates eight PCI interrupt signals (INTA-..INTH-) for use by PCI devices. The PCI interrupts are evenly distributed to minimize latency and wired as follows:

 

 

PCI

 

 

PCI

PCI

PCI

 

 

 

 

Slot 1

Slot 2

Slot 3

Slot 4

 

 

 

 

 

 

 

 

INTA-

 

INTA-

INTD-

INTB-

INTD-

 

 

 

 

 

 

INTB-

 

—

—

—

—

 

 

 

 

 

 

INTC-

Wired

INTB-

INTA-

INTC-

INTA-

 

 

 

 

 

 

 

 

 

INTD-

to

—

—

—

—

 

 

 

 

 

 

INTE-

 

—

—

—

—

 

 

 

 

 

 

INTF-

 

INTC-

INTB-

INTD-

INTB-

 

 

 

 

 

 

INTG-

 

INTD-

INTC-

INTA-

INTC-

 

 

 

 

 

 

INTH-

 

—

—

—

—

 

 

 

 

 

 

 

 

 

 

NOTES:

[1]Connection internal to the ICH. Will be reported by BIOS as using INTA but is NOT shared with other functions using INTA.

MT, CMT form factors only.

SFF, ST, MT, CMT form factors only.

The PCI interrupts can be configured by PCI Configuration Registers 60h..63h to share the standard ISA interrupts (IRQn).

✎The APIC mode is supported by the Windows NT, Windows 2000, and Windows XP operating systems. Systems running the Windows 95 or 98 operating system will need to run in 8259 mode.

Technical Reference Guide

361834-002

4-13