What is IRQ Steering?
IRQ Steering is a way for PCI motherboards to dynamically assign IRQs to PCI Devices. The assignment is done during the initial POST and can be achieved during normal operation of the computer. An example of how PCI Steering can dynamically assign IRQ resources can be observed when a PCI based laptop is hot docked into a docking station. The PCI bus does not consume IRQs in the strictest sense. Instead they consume IRQ pins. Each PCI slot has four IRQ pins connected to it and they are known as INTA, INTB, INTC and INTD. The combinations of slot number and IRQ pin is known as a Link value (i.e. the INTA wire on PCI slot 1 would have a link value of 1, while INTB on PCI slot 1 would have a value of 2). The BIOS contains a table that consists of the Slot number and Pin number. This is the IRQ steering table. Normally, these interrupt levels are transparent to the user, but can be accessed in the motherboards BIOS setup screen for PCI where they can be used to control individual PCI cards
