APIC(4) | Kernel Interfaces Manual (x86) | APIC(4) |
There are two elements in the architecture, the local APIC (LAPIC) and the I/O APIC. Historically these were connected by a dedicated 3-wire “APIC bus”, but the system bus is used for communication today. The configuration is increasingly dependent on ACPI.
Typically each CPU in the system contains one LAPIC that performs two primary functions:
There is typically one I/O APIC for each peripheral bus in the system. Each I/O APIC has a series of interrupt inputs to external interrupt sources. The architecture usually contains a redirection table which can be used to route the interrupts that an I/O APIC receives to one or more local APICs. When a LAPIC is able to accept an interrupt, it will signal the CPU. Without an I/O APIC, the local APICs are therefore mostly useless; one of the primary functions of the architecture is no longer achievable, interrupts can not be distributed to different CPUs.
The 8259 PIC has coexisted with the architecture since its introduction. It is still possible to disable the APIC system and revert back to a 8259-compatible PIC. But the widespread use of MP systems has made this mainly a fallback option.
Intel Corporation, Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A: System Programming Guide, Part 1, Chapter 10, January, 2011, http://www.intel.com/Assets/PDF/manual/253668.pdf.
Intel Corporation, Intel 82093AA I/O Advanced Programmable, Interrupt Controller (I/O APIC) Datasheet, May, 1996, http://www.intel.com/design/chipsets/datashts/29056601.pdf.
Intel Corporation, 8259A, Programmable Interrupt Controller, December, 1988, http://pdos.csail.mit.edu/6.828/2005/readings/hardware/8259A.pdf.
John Baldwin, PCI Interrupts for x86 Machines under FreeBSD, May 18-19, 2007, Proceedings of BSDCan 2007, http://people.freebsd.org/~jhb/papers/bsdcan/2007/article.pdf.
Microsoft Corporation, PCI IRQ Routing on a Multiprocessor ACPI System, December 4, 2001, http://www.microsoft.com/whdc/archive/acpi-mp.mspx.
June 6, 2011 | NetBSD 6.1 |