System Board
Assigned Device Interrupts
Chapter 2
61
Although you can use the Setup program to change some of the settings, the following
address map isn’t completely BIOS dependent but is determined partly by the operating
system. Note that some of the interrupts are allocated dynamically.
Three major interrupt modes are available:
• PIC mode: This mode uses only legacy interrupt controllers, so only one processor
can be supported. Because this system has dual-processor capability, Windows NT
doesn’t choose this mode as the default. However, during Windows NT installation,
you can select this mode.
• Virtual wire mode: This mode is implemented with APIC controllers in the ICH2
and P64H and used during boot time. The virtual wire mode allows the transition to
the symmetric I/O mode. In the virtual wire mode, only one processor executes
instructions.
• Symmetric I/O mode: This mode is implemented with APIC controllers in the
ICH2 and P64H and allows for multiple processor operations.
NOTE In PIC mode and virtual wire mode, PCI interrupts are routed to the INT line. In
symmetric I/O mode, PCI interrupts are routed to the I/O APIC controllers and
forwarded over an APIC bus to the processors.
Interrupt Source
APIC Controller Interrupt Signalling on
of device Input
(PIC
mode)
a
(APIC
modes)
INTA - PCI slot 3 (32/33) P64H IRQ0 BT_INT APIC bus
INTB - PCI slot 3 (32/33) P64H IRQ1 BT_INT APIC bus
INTC - PCI slot 3 (32/33) P64H IRQ2 BT_INT APIC bus
INTD - PCI slot 3 (32/33) P64H IRQ3 BT_INT APIC bus
INTA - PCI slot 4 (32/33) P64H IRQ4 BT_INT APIC bus
INTB - PCI slot 4 (32/33) P64H IRQ5 BT_INT APIC bus
INTC - PCI slot 4 (32/33) P64H IRQ6 BT_INT APIC bus
INTD - PCI slot 4 (32/33) P64H IRQ7 BT_INT APIC bus
INTA - onboard SCSI controller P64H IRQ8 BT_INT APIC bus
AGP - INTA, PCI Slot 1 - INTC, PCI
Slot 2 - INTA, PCI Slot 5 - INTB
ICH2 INTA INT APIC bus
PCI Audio - INTA, AGP - INTB, PCI
Slot 1 - INTD, PCI Slot 2 - INTB,
PCI Slot 5 - INTC
ICH2 INTB INT APIC bus
BT_INT, PCI Slot 1 - INTA, PCI
Slot 2 - INTC, PCI Slot 5 - INTD
ICH2 INTC INT APIC bus
USB - INTA, PCI Slot 1 - INTB, PCI
Slot 2 - INTD, PCI Slot 5 - INTA
ICH2 INTD INT APIC bus
Device on Primary IDE Channel ICH2 IRQ14 INT APIC bus
Device on Secondary IDE Channel ICH2 IRQ15 INT APIC bus
Serial Interrupt from Super I/O ICH2 SERIRQ INT APIC bus
a. In PIC mode, the interrupts signaled to the P64H are chained as INTC to the ICH2.
