Legacy Pin Interrupts Compared With Message Signalled Interrupts
The original PCI way to raise an interrupt was to pull on a physical wire shared with other cards, which means the handler must work out who it was and the line stays asserted until the device is told to stop. Message signalled interrupts replace the wire with a small memory write the card performs, so each card, and even each queue on a card, gets its own private interrupt with no sharing and no acknowledgment dance. A driver asks for the better kind first and falls back, because the two need different set-up and different handler code.
Questions this Concept answers
- Why does a message signalled interrupt remove the need for a handler to work out whether the interrupt was its own?
Legacy INTX, MSI, and MSI-X Interrupt Signaling in PCI Express
PCI Express interrupt signaling evolved through three mechanisms that trade off compatibility, scalability, and efficiency: legacy INTx emulation, which mimics classic PCI's four physical interrupt p…