I/O Interfaces & Buses

What is a characteristic of MSI (message-signaled interrupts) used in PCI Express?

  1. AThe device phones the CPU on every interrupt
  2. BNo interrupts are used; the CPU continuously polls the device
  3. CThe device signals an interrupt by writing to a designated address, so no dedicated interrupt wire is needed
Show answer and explanation

Answer: C. The device signals an interrupt by writing to a designated address, so no dedicated interrupt wire is needed

Older devices had dedicated interrupt wires, sometimes shared among several devices. With MSI, the device writes a designated value to an address set by the OS, and that write arrives at the CPU as an interrupt. Without the limit on wires, a device can have many interrupts; a network card, for example, can send a separate interrupt for each receive queue to a different core.

  • A. Of course no telephone is involved.
  • B. That is polling.
  • C. Correct. Interrupts are sent as packets too.
Practice this topic Back to topic

More I/O Interfaces & Buses questions

  1. What is the difference between bandwidth and latency in interface performance?
  2. On a link with 10 GB/s bandwidth and 1 µs latency, roughly how long does it take to send 64 bytes once (time = latency + size ÷ bandwidth)?
  3. Which is most effective for speeding up a program that exchanges thousands of small pieces of data with a device one at a time?
  4. Which statement about how USB communication works is correct (for conventional USB, excluding USB4)?
  5. Which statement about USB Type-C is correct?