MADT: Difference between revisions
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''This page is about the ACPI MADT (Multiple APIC Description Table)'',
==Introduction==
The MADT describes all of the interrupt controllers in the system. It can be used to enumerate the processors currently available.
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Based on the Entry Type field value, the rest of the record layout can be determined.
== Entry Type 0
This type represents a single logical processor and its local interrupt controller.
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If flags bit 0 is set the CPU is able to be enabled, if it is not set you need to check bit 1. If that one is set you can still enable it, if it is not the CPU can not be enabled and the OS should not try.
== Entry Type 1
This type represents a I/O APIC. The global system interrupt base is the first interrupt number that this I/O APIC handles. You can see how many interrupts it handles using the register by getting the number of redirection entries from register 0x01, as described in [[APIC#IO_APIC_Registers|IO APIC Registers]].
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== Entry Type 2
This entry type contains the data for an Interrupt Source Override.
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== Entry type 3
Specifies which IO/APIC interrupt inputs should be enabled as non-maskable.
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== Entry Type 4
Configure these with the LINT0 and LINT1 entries in the Local vector table of the relevant processor(')s(') local APIC.
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== Entry Type 5
Provides 64 bit systems with an override of the physical address of the Local APIC. There can only be one of these defined in the MADT. If this structure is defined, the 64-bit Local APIC address stored within it should be used instead of the 32-bit Local APIC address stored in the MADT header.
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▲== Entry Type 9 : Processor Local x2APIC ==
Represents a physical processor and its Local x2APIC. Identical to Local APIC; used only when that struct would not be able to hold the required values.
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Here is a diagram of the interrupt types:
http://i.imgur.com/HRDwoa6.png
== Example Code ==
{{Disputed}}
The following code snippet detects and parses MADT table to collect Local APIC data on SMP systems. Works with both [[RSDT]] and [[XSDT]], and compiles for both protected mode and long mode.
<source lang="c">
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