Advanced Programmable Interrupt Controller: Difference between revisions

Revision as of 17:51, 20 December 2024

Revision as of 01:00, 10 January 2025

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The first-generation Intel APIC chip, the 82489DX, which was meant to be used with [[Intel 80486]] and early Pentium processors, is actually an external local and I/O APIC in one circuit. The Intel MP 1.4 specification refers to it as "discrete APIC" in contrast with the "integrated APIC" found in most of the Pentium processors.<ref>[http://www.intel.com/design/archives/processors/pro/docs/242016.htm Intel MultiProcessor Specification], version 1.4, page 1-4, May 1997</ref> The 82489DX had 16 interrupt lines;<ref name="Ram2001">{{cite book|author=Badri Ram|title=Adv Microprocessors Interfacing|url=https://books.google.com/books?id=eVcEWDIeTYcC&pg=PT314|year=2001|publisher=Tata McGraw-Hill Education|isbn=978-0-07-043448-6|page=314}}</ref> it also had a quirk that it could lose some ISA interrupts.<ref >{{cite web | website=freebsd.org|title=A Description of the APIC I/O Subsystem | url=http://people.freebsd.org/~fsmp/SMP/papers/apicsubsystem.txt | access-date=14 May 2023}}</ref>

In a multiprocessor 486 system, each CPU had to be paired with its own 82489DX; additionally a supplementary 82489DX had to be used as I/O APIC. The 82489DX could not emulate the 8259A (XT-PIC) so these also had to be included as physical chips for backwards compatibility.<ref>Intel MultiProcessor Specification, version 1.4, page 5-3, May 1997</ref> The 82489DX was a packaged as a 132-pin [[PQFP]].<ref name="Ram2001"/>

==Integrated local APICs==