Pci Interrupt Routing Map - Intel BLKDQ965GFEKR Technical Product Specification

2.6

PCI Interrupt Routing Map

This section describes interrupt sharing and how the interrupt signals are connected
between the PCI bus connectors and onboard PCI devices. The PCI specification
specifies how interrupts can be shared between devices attached to the PCI bus. In
most cases, the small amount of latency added by interrupt sharing does not affect
the operation or throughput of the devices. In some special cases where maximum
performance is needed from a device, a PCI device should not share an interrupt with
other PCI devices. Use the following information to avoid sharing an interrupt with a
PCI add-in card.
PCI devices are categorized as follows to specify their interrupt grouping:
• INTA: By default, all add-in cards that require only one interrupt are in this
category. For almost all cards that require more than one interrupt, the first
interrupt on the card is also classified as INTA.
• INTB: Generally, the second interrupt on add-in cards that require two or more
interrupts is classified as INTB. (This is not an absolute requirement.)
• INTC and INTD: Generally, a third interrupt on add-in cards is classified as INTC
and a fourth interrupt is classified as INTD.
The ICH8DO has eight Programmable Interrupt Request (PIRQ) input signals. All PCI
interrupt sources either onboard or from a PCI add-in card connect to one of these
PIRQ signals. Some PCI interrupt sources are electrically tied together on the board
and therefore share the same interrupt. Table 16 shows an example of how the
PIRQ signals are routed.
Table 16. PCI Interrupt Routing Map
PCI Interrupt Source
ICH8DO LAN
PCI bus connector 1
PCI bus connector 2
IEEE-1394a controller
NOTE
In PIC mode, the ICH8DO can connect each PIRQ line internally to one of the IRQ
signals (3, 4, 5, 6, 7, 9, 10, 11, 12, 14, and 15). Typically, a device that does not
share a PIRQ line will have a unique interrupt. However, in certain interrupt-
constrained situations, it is possible for two or more of the PIRQ lines to be connected
to the same IRQ signal. Refer to Table 15 for the allocation of PIRQ lines to IRQ
signals in APIC mode.
PCI interrupt assignments to USB ports, Serial ATA ports, and PCI Express ports are
dynamic.
ICH8DO PIRQ Signal Name
PIRQA PIRQB PIRQC
Technical Reference
PIRQD PIRQE PIRQF
INTA
INTD INTA
INTC INTB
INTA
PIRQG PIRQH
INTB INTC
INTA INTD
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