TerraTec PHASE 22 Manual page 42

The result is that:
·
PCI slot 2, 6 and AGP port share an IRQ.
· PCI slot 3, onboard 1394 (FireWire) and SATA share an IRQ.
·
PCI slot 4 and onboard LAN share an IRQ.
·
PCI slot 1 and 5 share an IRQ.
· the IDE controller has its own IRQ.
·
the USB controllers have their own IRQ.
·
the AC97 sound chip has its own IRQ.
As you can see the installation position has a great influence on the IRQ assignment in
the system, and to assign an IRQ to a device you can, for example, use the second PCI
slot on the ABIT board but then you must leave the third free. For example, on the ASUS
board that would be slots 1 and 5.
To check the IRQ assignments in your system, open the Device Manager in Windows 98
and ME, double-click System, and you will find the IRQ list there. In Windows 2000 and
XP the Control Panel does not usually show the IRQ assignments correctly because of
virtual CPI IRQ assignments. In these operating systems you must view the PCI Device
List, which appears briefly during the boot process. The "actual" IRQ assignments are
shown there, but with modern PCs there is usually no time to look at the list during
startup, because it appears and disappears much too quickly. Tip: select the floppy disk
drive as the first boot device and insert an empty diskette. When the error message warn-
ing of a missing operating system appears, you will also be able to see the PCI Device
List ;-).
Exclusive or shared IRQ?
Basically, all modern PCI cards with WDM drivers support IRQ sharing, but under some
circumstances this can cause problems. For example, if the sound card requests an inter-
rupt request during playback or recording of an audio file but the request cannot be car-
ried out immediately, perhaps because the ISDN card is also using this IRQ and the IRQ
controller must first query which device is actually requesting the IRQ, this can cause in-
terference like static and crackling as a result of missing samples.
Our hearing is (fortunately) one of our most sensitive organs and therefore every sample
that is missed during playback is immediately obvious. Your eyes would not even notice a
brief delay during web surfing caused by the ISDN card not reacting immediately, but your
ears are less forgiving. So this apples for sound cards: give it its own IRQ to keep your
ears happy!
42 PHASE 22 (English)