3.5. Advanced Programmable Interrupt Controller

The advanced programmable interrupt controller (APIC) was developed by Intel® to provide the ability to handle large amounts of interrupts, to allow each of these to be programmatically routed to a specific set of available CPUs (and for this to be changed accordingly), to support inter-CPU communication, and to remove the need for a large number of devices to share a single interrupt line.

APIC represents a series of devices and technologies that work together to generate, route, and handle a large number of hardware interrupts in a scalable and manageable way. It uses a combination of a local APIC built into each system CPU, and a number of Input/Outpt APICs that are connected directly to hardware devices. When a hardware device generates an interrupt, it is detected by the IO-APIC it is connected to, and then routed across the system APIC bus to a particular CPU. The operating system knows which IO-APIC is connected to which device, and to which particular interrupt line within that device because of a combination of information sources. Firstly, there is the ACPI DSDT (Advanced Configuration and Power Interface Differentiated System Description Table) that includes information about the specific wiring of the host system motherboard and peripheral components. Secondly, a device provides certain information about its available interrupt sources. Together, these two sets of data provide information about the overall interrupt hierarchy.

Complex APIC-based interrupt management strategies are possible, with the system APICs connected in hierarchies, and delivering interrupts to CPUs in a load-balanced fashion rather than targeting a specific CPU or set of CPUs.