Intel D915GLVGL Manuale Utente

 45 

This section describes interrupt sharing and how the interrupt signals are connected between the 
PCI Conventional bus connectors and onboard PCI Conventional devices.  The PCI Conventional 
specification describes how interrupts can be shared between devices attached to the PCI 
Conventional 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 Conventional device should not share an interrupt with 
other PCI Conventional devices.  Use the following information to avoid sharing an interrupt with a 
PCI Conventional add-in card. 

PCI Conventional 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 ICH6 has eight Programmable Interrupt Request (PIRQ) input signals.  All PCI Conventional 
interrupt sources either onboard or from a PCI Conventional add-in card connect to one of these 
PIRQ signals.  Some PCI Conventional interrupt sources are electrically tied together on the board 
and therefore share the same interrupt.  Table 14 shows an example of how the PIRQ signals are 
routed.   

For example, using Table 14 as a reference, assume an add-in card using INTA is plugged into PCI 
Conventional bus connector 3.  In PCI bus connector 3, INTA is connected to PIRQB, which is 
already connected to the ICH6 audio controller.  The add-in card in PCI Conventional bus 
connector 3 now shares an interrupt with the onboard interrupt source. 

ICH6 

LAN 

    INTA 

   

PCI bus connector 1 

 

 

 

 

INTD 

INTA 

INTB 

INTC 

PCI bus connector 2 

 

 

 

 

INTC 

INTB 

INTA 

INTD