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RSDP: Difference between revisions
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{{ACPI}}
'''RSDP''' (Root System Description Pointer) is a data structure used in the [[ACPI]] programming interface.
In ACPI Version 1.0 it has this structure:
<
struct
char Signature[8];
uint8_t Checksum;
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uint32_t RsdtAddress;
} __attribute__ ((packed));
</syntaxhighlight>
since Version 2.0 it has been extended
<
struct
char Signature[8];
uint8_t Checksum;
char OEMID[6];
uint8_t Revision;
uint32_t RsdtAddress; // deprecated since version 2.0
uint32_t Length;
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uint8_t reserved[3];
} __attribute__ ((packed));
</syntaxhighlight>
==Detecting the RSDP==
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If you're using UEFI, you can find it somewhere in EFI_SYSTEM_TABLE. Thus, there's no need for searching the RAM.
'''Note''': The standard methods to find the RSDP may not work on UEFI systems. Because of that, finding it inside EFI_SYSTEM_TABLE is the correct and reliable method (see ACPI 6.2 section 5.2.5.2 'Finding the RSDP on UEFI Enabled Systems').
When booting with a multiboot2 compliant loader, a copy of the RSDP is contained in the ACPI new RSDP or ACPI old RSDP tag respectively.
==Validating the RSDP==
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The size of the entire table since offset 0 to the end.
==== Xsdt Address ====
64-bit physical address of the [[XSDT]] table. If you detect ACPI Version 2.0 you should use this table instead of RSDT even on
==== Extended Checksum ====
This field is used to calculate the checksum of the entire table, including both checksum fields.
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== What's next? ==
Well, you should now parse the [[RSDT]] (or [[XSDT]]).
[[Category:ACPI]]
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