User manual TERRATEC INTERRUPT REQUEST TUTORIAL

[. . . ] Interrupt Request Tutorial IRQ ­ the unsolved mystery, or not? Basics IRQ stands for "Interrupt Request", IRQs communicate to the processor when a device wants to carry out a specific command. This is called the interrupt request, which is capable of stopping the processor and directing it to perform a specific function. [. . . ] There are no general rules governing this and the mainboard documentation proves to be the savior in such cases. Using the , , ABIT KT7A-Raid" and the , , ASUS A7V8X" as examples, let us take a closer look: ABIT KT7A-Raid 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 shared shared B shared shared C shared shared D shared shared shared A through D represent the 4 available IRQs belonging to the PCI bus. · · · · A B C D represents PCI slot 1 and the AGP slot. represents PCI slots 4, 6, and the USB controller. This means: · · · · PCI PCI PCI PCI slot 1 and the AGP slot share an IRQ slots 2 and 3 share an IRQ slot 4, 6, and the USB controller share an IRQ slot 5 and the Raid controller share an IRQ Page 2 of 4 TerraTec Electronic GmbH ­ Herrenpfad 38 ­ 41334 Nettetal ­ Germany ­ Tel: +49-2157-8179-0 ­ Fax: +492157-8179-22 Interrupt Request Tutorial ASUS A7V8X Device A B C D PCI slot 1 shared PCI slot 2 shared PCI slot 3 shared PCI slot 4 shared PCI slot 5 shared PCI slot 6 shared AGP slot shared USB 1. 1 UHCI 1 USB 1. 1 UHCI 2 USB 1. 1 UHCI 3 USB 2. 0 EHCI AC `97 (Sound) Onboard LAN shared Onboard shared 1394 Onboard SATA shared Onboard IDE E used F shared shared shared shared G used H - A through H represent the 8 available IRQs belonging to the PCI bus. · · · · · · · · A represents PCI slots 2, 6, and the AGP slot. H is not used This means: · · · · · PCI slot 2, 6, and the AGP port share an IRQ. The IDE controller has its own IRQ. Page 3 of 4 TerraTec Electronic GmbH ­ Herrenpfad 38 ­ 41334 Nettetal ­ Germany ­ Tel: +49-2157-8179-0 ­ Fax: +492157-8179-22 Interrupt Request Tutorial · · The USB controller has its own IRQ. The AC `97 soundchip has its own IRQ. As you see, the slot choice has a very large influence on the systems IRQ assignment and to insure a device receives its own IRQ one can, using the board from ABIT as an example, use the 2nd PCI slot - but the 3rd must then remain unused. In order to control the systems IRQ assignments under Windows 98 and ME go to the Windows Control Panel and double click on the System icon, where the IRQ list can be viewed. Under Windows 2000 and XP the Device Manager does not correctly reflect the IRQ assignments because of the virtual ACPI IRQ layer. When using these operating systems the PCI Device List must be consulted­ this is displayed briefly during the boot phase. There the , , real"(physical) IRQ assignment is shown, but most modern PCs boot so fast that this is displayed very briefly. [. . . ] The eyes don't mind when a tiny hesitation delays the display of an internet page because the ISDN controller reacted slowly, but the ears are an entirely different story. And so for soundcards: Give them their own IRQ and your ears will be pleased! Page 4 of 4 TerraTec Electronic GmbH ­ Herrenpfad 38 ­ 41334 Nettetal ­ Germany ­ Tel: +49-2157-8179-0 ­ Fax: +492157-8179-22 [. . . ]