RSDT: Difference between revisions

'''RSDT''' (Root System Description Table) is a data structure used in the [[ACPI]] programming interface. This table contains pointers to all the other System Description Tables.

 

The RSDT is the main System Description Table. However there are many kinds of SDT. All the SDT may be split into two parts. One (the header) which is common to all the SDT and another (data) which is different for each table.

The structure of the header is:

struct ACPISDTHeader {

char Signature[4];

uint32_t CreatorRevision;

};

=== Header fields ===

==== Signature ====

==== Checksum ====

A 8-bit checksum field of the whole table, inclusive of the header. All bytes of the table summed must be equal to 0 (mod 0x100). You should always do a checksum of the table before using it, even if you found the table linked by other tables.

bool doChecksum(ACPISDTHeader *tableHeader)

{

return sum == 0;

}

 

=== Other fields ===

In case you used RsdtPointer, the complete table structure is:

struct RSDT {

struct ACPISDTHeader h;

uint32_t PointerToOtherSDT[(h.Length - sizeof(h)) / 4];

};

If you instead used the XsdtPointer, then the table is:

struct XSDT {

struct ACPISDTHeader h;

uint64_t PointerToOtherSDT[(h.Length - sizeof(h)) / 8];

};

 

== How to use ==

Well, suppose you want to find the [[FADT]]. The FADT, being a SDT has a ACPISDTHeader. It's signature is "FACP".

You may use this code:

void *findFACP(void *RootSDT)

{

return NULL;

}

 

== What can you find? ==