FreeBSD Device Drivers

Chapter 8. Interrupt Handling

Hardware devices often have to perform (or deal with) external events, such as spinning disk platters, winding tapes, waiting for I/O, and so on. Most of these external events occur in a timeframe that is much slower than the processor’s—that is, if the processor were to wait for the completion (or arrival) of these events, it would be idle for some time. To avoid wasting the processor’s valuable time, interrupts are employed. An interrupt is simply a signal that a hardware device can send when it wants the processor’s attention (Corbet et al., 2005). For the most part, a driver only needs to register a handler function ...