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. Since the introduction of PIC (Programmable Interrupt Controller) 16 Interrupt conductors are available in a PC, Most of these, as demonstrated in the diagram below, are already allocated, More Modern mainboards usually utilize the APIC (Advanced Programmable Interrupt Controller) standard, which can manage more than 32 IRQs. IRQ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Device Assignment System Timer Keyboard Link to second IRQ controller (IRQ 8 to 15); since AT replaced by IRQ 9 Serial port 2 (COM2) Serial port 1 (COM1) Available Floppy Disk Controller Parallel Port 1 (LPT1) Real-time Clock Available Available Available PS/2 Mouse Math Coprocessor Primary IDE Controller Secondary IDE Controller Unfortunately the PC isn't yet ready to be used as no graphic card IRQ reservation has been provided for. [. . . ] Every mainboard has an IRQ table for the PCI bus. 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 slot 5 and the Raid controller. 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. B represents PCI slot 3, Onboard 1394 (FireWire), and SATA. C represents PCI slot 4 and Onboard LAN. H is not used This means: · · · · · PCI slot 2, 6, and the 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. 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. On the ASUS board this correlates to slots 1 and 5. [. . . ] Our hearing is (luckily) a very sensitive organ, capable of immediately recognizing playback errors caused by such a sample drop. 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 [. . . ]