Pci Interrupt Routing Map; Pci Device Classes - Intel MS440GX Product Manual

MS440GX Motherboard Product Guide

PCI Interrupt Routing Map

This section describes interrupt sharing and how the interrupt signals are connected between the
PCI expansion slots and onboard PCI devices. The PCI specification states 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.
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. Table 60 specifies the PCI device classifications identifying their interrupt group.
Table 60.

PCI Device Classes

Device Classification
INTA
INTB
INTC
INTD
The PIIX4E PCI-to-ISA bridge has four programmable interrupt request (PIRQ) input signals.
Any PCI interrupt source (either onboard or from a PCI add-in card) connects to one of these PIRQ
signals.
Because there are only four signals, some PCI interrupt sources are mechanically tied together on
the motherboard and, therefore, share the same interrupt. Table 60 lists the PIRQ signals and
shows how the signals are connected to the PCI expansion slots and to onboard PCI interrupt
sources.
Table 61.

PCI Interrupt Routing Map

PIIX4E
PIRQ PCI
Signal Slot 1
PIRQA INTA
PIRQB INTB
PIRQC INTC
PIRQD INTD
108
Class Definition/Specification
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.
Generally, the second interrupt on add-in cards that require two or more
interrupts is classified as INTB. (This is not an absolute requirement.)
Generally, a third interrupt on add in cards is classified as INTC.
Generally, a fourth interrupt on add in cards is classified as INTD.
PCI PCI PCI
Slot 2: Slot 3: Slot 4:
INTD INTC INTB
INTA INTD INTC
INTB INTA INTD
INTC INTB INTA
PCI PCI
Slot 5: Slot 6: A.G.P.
INTA INTD INTA
INTB INTA INTB
INTC INTB
INTD INTC
PCI Power
LAN Management
X
X