TerraTec PHASE 22 Manual page 40

There are generally only four "real" interrupt inputs available for the PCI bus, eight with
modern motherboards with APIC. This means that even if you have six PCI slots on your
motherboard, they have to make do with four or eight IRQs. The AGP port, USB and pos-
sibly the Raid controller also use these IRQs and with newer cards there is also onboard
LAN, 1394 (FireWire) and SATA (serial ATA - new transfer standard for hard disks). It is
impossible to avoid sharing an interrupt between multiple PCI slots. Unfortunately, there
are no rules covering this and the motherboard documentation is the only refuge. Every
motherboard has an IRQ table for the PCI bus; we will explain this assignment in more
detail with the example of the "ABIT KT7A-Raid" and the "ASUS A7V8X":
Device
PCI Slot 1
PCI Slot 2
PCI Slot 3
PCI Slot 4
PCI Slot 5
PCI Slot 6
AGP Slot
USB Controller
Raid Controller
A to D stands for the four available IRQs on the PCI bus.
·
A is available for PCI slot 1 and AGP slot.
·
B is available for PCI slot 2 and 3.
· C is available for PCI slot 5 and the Raid controller.
·
D is available for PCI slot 4, 6 and the USB controller.
The result is that:
·
PCI slot 1 and AGP slot share an IRQ
· PCI slot 2 and 3 share an IRQ
·
PCI slot 4, 6 and USB controller share an IRQ
·
PCI slot 5 and Raid controller share an IRQ
40
ABIT KT7A-Raid
A
shared
- shared
- shared
-
-
shared
-
B C
- -
-
-
- -
- shared
- -
- -
shared
D
-
-
-
shared
shared
-
shared
PHASE 22 (English)