Advanced Configuration and Power Interface Specification

ACPI Software Programming Model
5.2.7 Root System Description Table (RSDT)
OSPM locates that Root System Description Table by following the pointer in the RSDP structure.
The RSDT, shown in Table 5-32, starts with the signature ‘RSDT’ followed by an array of physical
pointers to other system description tables that provide various information on other standards
defined on the current system. OSPM examines each table for a known signature. Based on the
signature, OSPM can then interpret the implementation-specific data within the table.
Platforms provide the RSDT to enable compatibility with ACPI 1.0 operating systems. The XSDT,
described in the next section, supersedes RSDT functionality.
Table 5-32 Root System Description Table Fields (RSDT)
Field
Byte
Length
Byte
Offset Description
Header
Signature 4 0 ‘RSDT’ Signature for the Root System Description Table.
Length 4 4 Length, in bytes, of the entire RSDT. The length implies the
number of Entry fields (n) at the end of the table.
Revision 1 8 1
Checksum 1 9 Entire table must sum to zero.
OEMID 6 10 OEM ID
OEM Table ID 8 16 For the RSDT, the table ID is the manufacture model ID. This
field must match the OEM Table ID in the FADT.
OEM Revision 4 24 OEM revision of RSDT table for supplied OEM Table ID.
Creator ID 4 28 Vendor ID of utility that created the table. For tables containing
Definition Blocks, this is the ID for the ASL Compiler.
Creator Revision 4 32 Revision of utility that created the table. For tables containing
Definition Blocks, this is the revision for the ASL Compiler.
Entry 4*n 36 An array of 32-bit physical addresses that point to other
DESCRIPTION_HEADERs. OSPM assumes at least the
DESCRIPTION_HEADER is addressable, and then can further
address the table based upon its Length field.
5.2.8 Extended System Description Table (XSDT)
The XSDT provides identical functionality to the RSDT but accommodates physical addresses of
DESCRIPTION HEADERs that are larger than 32 bits. Notice that both the XSDT and the RSDT
can be pointed to by the RSDP structure. An ACPI-compatible OS must use the XSDT if present.
Table 5-33 Extended System Description Table Fields (XSDT)
Field
Byte
Length
Byte
Offset
Description
Header
Signature 4 0 ‘XSDT’. Signature for the Extended System Description Table.
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