Interrupts: How Hardware Asks for Attention
Why devices use interrupt signaling instead of requiring the processor to repeatedly ask whether work is ready.
Polling and signaling differ
Polling repeatedly checks a device state, while an interrupt lets hardware signal that an event needs service. The host environment and driver then coordinate which handler, queue, or deferred routine represents that event.
An interrupt is not the whole request
The signal may indicate completion, new data, a state change, or a condition requiring attention. The driver still reads device state, acknowledges the source, and associates the event with the correct request and lifecycle.
Deferred work protects timing
Interrupt handling has strict timing and context constraints. Drivers commonly separate immediate acknowledgement from later processing so that more substantial work occurs where the host environment permits it.
Shared lines need identity
When resources are shared, a handler must determine whether an event belongs to its device before acting on it. Device identity, register state, and documented interrupt semantics provide that boundary.
Reference facts
- Interrupt role
- A device-to-processor signal for an event requiring coordinated service.
- Lifecycle
- Signal, acknowledge, associate, and defer work according to the device contract.
Questions and answers
Does every interrupt mean data is ready?
No. It can represent completion, status, power, errors, or another device-defined event.
Why defer interrupt work?
Immediate handlers have context and timing constraints; deferred routines allow the stack to process more work under the host environment’s rules.