Date: Sun, 17 Nov 1996 03:57:21 +1100 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, se@freebsd.org Cc: hackers@freebsd.org, mrcpu@cdsnet.net Subject: Re: IRQ sharing on PCI? Message-ID: <199611161657.DAA23158@godzilla.zeta.org.au>
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>> >This depends on the PCI BIOS, which is free >> >to assign any IRQ to any PCI Int line. >> >PCI requires shared interrupts to work, since >> >there are far less real interrupt request >> >inputs in a typical system, than independent >> >PCI Int lines. >... >This means that there are in fact four PCI Int lines, but >most PCI cards will only use Int A. multi-function devices >will use Int A and Int B, if two functions are implemented >(see the AMD SCSI+Ethernet Combo chip), or all four lines >if there are four functions on a chip (announced 4 channel >Ethernet cards). And if you are using a PCI to PCI bridge >(current 4 channel Ethernet cards and the AH3940 or PCI bus >extender boxes, for example), then the PCI Int lines used >will depend on the slots used on the secondary side of the >PCI bridge. (The scheme used is meant to randomize PCI Int But these aren't typical :-). Now that Pentiums and PCI are common in typical (cheap) systems, I guess that a typical PCI system has 0 or 1 (unused) PCI interrupts depending on whether vga0 has one :-]. Why aren't PCI interrupts used for motherboard i/o, at least optionally? BTW, `pciconf -r' dumps core after printing the usage message. Bruce Bruce
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