Writing Device Drivers

Polled Interrupts

In polled (or autovectored) devices, the only information the system has about a device interrupt is either the bus interrupt priority level (IPL, on an SBus in a SPARC machine, for example) or the interrupt request number (IRQ on an ISA bus in an x86 machine, for example).

When an interrupt handler is registered, the system adds the handler to a list of potential interrupt handlers for each IPL or IRQ. Once the interrupt occurs, the system must determine which device, of all the devices associated with a given IPL or IRQ, actually interrupted. It does this by calling all the interrupt handlers for the designated IPL or IRQ, until one handler claims the interrupt.

The SBus, ISA, EISA, MCA, and PCI buses are capable of supporting polled interrupts.