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PCI I/O Subsystem
5.5
Interrupt Routing
The board interrupt architecture accommodates both PC-compatible PIC mode and APIC mode
interrupts through use of the integrated I/O APICs in the ICH4.
5.5.1
Legacy Interrupt Routing
For PC-compatible mode, the ICH4 provides two 82C59-compatible interrupt controllers. The
two controllers are cascaded with interrupt levels 8-15 entering on level 2 of the primary
interrupt controller (standard PC configuration). A single interrupt signal is presented to the
processors, to which only one processor will respond for servicing. The ICH4 contains
configuration registers that define which interrupt source logically maps to I/O APIC INTx pins.
The ICH4 handles both PCI and IRQ interrupts. The ICH4 translates these to the APIC bus. The
numbers in the table below indicate the ICH4 PCI interrupt input pin to which the associated
device interrupt (INTA, INTB, INTC, INTD) is connected. The ICH4 I/O APIC exists on the I/O
APIC bus with the processors.
Interrupt
AGPA#
AGPB#
VGA#
sATA#
NIC1#
NIC2#
P64H2-A# [P1/P2]
P64-C Slot 5
P64-B Slot 4
P64-B Slot 3
P32-A Slot 2
P32-A Slot 1
5.5.2
APIC Interrupt Routing
For APIC mode, the baseboard interrupt architecture incorporates three Intel
to manage and broadcast interrupts to local APICs in each processor. The Intel I/O APICs
monitor each interrupt on each PCI device, including PCI slots in addition to the ISA
compatibility interrupts IRQ(0-15).
When an interrupt occurs, a message corresponding to the interrupt is sent across a three-wire
serial interface to the local APICs. The APIC bus minimizes interrupt latency time for
compatibility interrupt sources. The I/O APICs can also supply greater than 16 interrupt levels to
the processor(s). This APIC bus consists of an APIC clock and two bidirectional data lines.
40
Table 16. PCI Interrupt Routing/Sharing
INT A
ICH4_PIRQA#
ICH4_PIRQB#
ICH4_PIRQB#
ICH4_PIRQD#
ICH4-PIRQC#
P1-IRQ4#
ICH4_PIRQE#
P1_IRQ0#
P1_IRQ1#
P2_IRQ0#
P2_IRQ1#
P2_IRQ4#
P2_IRQ5#
ICH4_PIRQG#
ICH4_PIRQF#
ICH4_PIRQF#
ICH4_PIRQG#
Intel part number C32194-002
Intel® Server Board SE7505VB2
INT B
INT C
P1_IRQ2#
P2_IRQ2#
P2_IRQ6#
ICH4_PIRQE#
ICH4_PIRQH#
INT D
P1_IRQ3#
P2_IRQ3#
P2_IRQ7#
ICH4_PIRQH#
ICH4_PIRQE#
®
I/O APIC devices
Revision 1.2
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