Two Methods of Interrupt Delivery
Interrupt delivery is conditionally optional for PCI Express devices. When a native PCI Express function does depend upon delivering interrupts to call its device driver, Message Signaled Interrupts (MSI) must be used. However, in the event that a device connecting to a PCI Express link cannot use MSIs (i.e., legacy devices), an alternate mechanism is defined. Both mechanisms are summarized below:
Native PCI Express Interrupt Delivery — PCI Express eliminates the need for sideband signals by using the Message Signaled Interrupt (MSI), first defined by the 2.2 version of the PCI Specification (as an optional mechanism) and later required by PCI-X devices. The term “Message Signaled Interrupt” can be misleading ...
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