This section provides background information regarding the standard PCI interrupt delivery using INTx signals. This is followed by a detailed discussion of how PCI Express supports virtual INTx signaling. Readers familiar with PCI interrupt handling may wish to proceed to “Virtual INTx Signaling” on page 347.
PCI devices that use interrupts have two options:
INTx# active low-level signals that can be shared. These signals were defined in the original specification.
Message Signaled Interrupts introduced with the 2.2 version of the specification are optional for PCI devices. These MSIs are compatible with PCI Express and require no modification by devices or by PCI Express-to-PCI ...