PCI Routing Map
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The PCI specification shows 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.

The ICH2 PCI-to-LPC bridge has eight programmable interrupt request (PIRQ) input signals. All PCI interrupt sources connect to one of these PIRQ signals. Because there are only eight signals, some PCI interrupt sources are mechanically tied together on the D810E2CB board, and therefore, share the same interrupt.

The following table lists the PIRQ signals and shows how the signals are connected to the on-board PCI interrupt sources.

For example, using as a reference, assume an add-in card using INTA is plugged into PCI bus connector 2. In PCI bus connector 2, INTA is connected to PIRQF, which is already connected to the SMBus. The add-in card in PCI bus connector 2 now shares interrupts with these on-board interrupt sources.

PCI interrupt routing map
PCI interrupt sourceICH2 PIRQ signal name
PIRQCPIRQFPIRQGPIRQBOther
ICH2 USB controller    INTD to PIRQD
SMBus controller   INTB 
ICH2 USB controller    INTC to PIRQH
ICH2 Audio   INTB 
ICH2 LAN    INTA to PIRQE
PCI Bus Connector 1 (J3B1)INTAINTBINTCINTD 
PCI Bus Connector 2 (J3A2)INTDINTAINTBINTC 

Note: The ICH2 can connect each PIRQ line internally to one of the IRQ signals (3, 4, 5, 6, 7, 10, 11, 14, and 15). Typically, a device that does not share a PIRQ line has 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.