The PCI spec permits a PCI function to generate an interrupt in one of three ways:
The method defined in the earlier versions of the PCI spec required the PCI function to assert an interrupt pin. The pin is tied to a trace that delivers the interrupt request to an input on the interrupt controller.
The later versions of the PCI spec defined the Message Signaled Interrupt (MSI) method.
The 3.0 PCI spec defined the MSI-X method.
The MSI and MSI-X methods are also supported in PCI-X and in PCI Express. In order to support the MSI method, an adapter must implement the following PCI configuration registers:
The MSI Address register.
The MSI Data register.
The MSI Control register.
In order to support the MSI-X ...