Does USB 2.0 provide interrupts for connected devices?

Question

I know every USB device has a control pipe, however I read somewhere that USB doesn't allow it to trigger an interrupt WHILE the device is connected. Thanks!

Answer 1

No idea - try ServerFault - it's more infrastructure related.

Answer 2

I doubt you care about an interrupt on CPU level, but there are interrupts in the USB protocol.

USB 2.0 defined 4 types of transfer methods:

From Wikipedia:

• isochronous transfers: at some guaranteed data rate (often, but not necessarily, as fast as possible) but with possible data loss (e.g. realtime audio or video).
• interrupt transfers: devices that need guaranteed quick responses (bounded latency) (e.g. pointing devices and keyboards).
• bulk transfers: large sporadic transfers using all remaining available bandwidth, but with no guarantees on bandwidth or latency (e.g. file transfers).
• control transfers: typically used for short, simple commands to the device, and a status response, used, for example, by the bus control pipe number 0.

AFAIK they aren't real interrupts though, polling will actually be done, but on the software side it should feel like an interrupt.