Interrupt Usage and Flexibility

A driver for a device that supports many different interruptible conditions must be able to map those conditions to an arbitrary number of interrupt vectors. The driver cannot assume that interrupt vectors that are allocated will remain available. Some currently available interrupts might later be taken back by the system to accommodate the needs of other drivers in the system.

A driver must be able to:

• Determine how many interrupts its hardware supports.

• Determine how many interrupts are appropriate to use. For example, the total number of processors in the system might affect this evaluation.

• Compare the number of interrupts needed with the number of interrupts available at any given time.

In summary, the driver must be able to select a mixture of interrupt handling functions and program its hardware to generate interrupts according to need and interrupt availability. In some cases multiple interrupts might be targeted to the same vector, and the interrupt handler for that interrupt vector must determine which interrupts occurred. The performance of the device can be affected by how well the driver maps interrupts to interrupt vectors.