Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
In theory, it might be possible to define something like PCI configuration space in a Definition
Block by building it from I/O space, but that is not the goal of the definition block. Such a space is
usually defined as a “built in” operator.
Some AML operators perform simple functions, and others encompass complex functions. The
power of the Definition block comes from its ability to allow these operations to be glued together in
numerous ways, to provide functionality to OSPM.
The AML operators defined in this specification are intended to allow many useful hardware designs
to be easily expressed, not to allow all hardware designs to be expressed.
Note: To accommodate addressing beyond 32 bits, the integer type was expanded to 64 bits in ACPI
2.0, see Section 19.3.5, “ASL Data Types”. Existing ACPI definition block implementations may
contain an inherent assumption of a 32-bit integer width. Therefore, to maintain backwards
compatibility, OSPM uses the Revision field, in the header portion of system description tables
containing Definition Blocks, to determine whether integers declared within the Definition Block
are to be evaluated as 32-bit or 64-bit values. A Revision field value greater than or equal to 2
signifies that integers declared within the Definition Block are to be evaluated as 64-bit values. The
ASL writer specifies the value for the Definition Block table header’s Revision field via the ASL
Definition Block’s ComplianceRevision field. See Section 19.6.28, “DefinitionBlock (Declare
Definition Block)”, for more information. It is the responsibility of the ASL writer to ensure the
Definition Block’s compatibility with the corresponding integer width when setting the
ComplianceRevision field.
5.2.11.1 Differentiated System Description Table (DSDT)
The Differentiated System Description Table (DSDT) is part of the system fixed description. The
DSDT is comprised of a system description table header followed by data in Definition Block
format. This Definition Block is like all other Definition Blocks, with the exception that it cannot be
unloaded. See Section 5.2.11, “Definition Blocks,” for a description of Definition Blocks. During
initialization, OSPM finds the pointer to the DSDT in the Fixed ACPI Description Table (using the
FADT’s DSDT or X_DSDT fields) and then loads the DSDT to create the ACPI Namespace.
Table 5-42 Differentiated System Description Table Fields (DSDT)
Field
Byte
Length
Byte
Offset
Description
Header
Signature 4 0 ‘DSDT’ Signature for the Differentiated System Description
Table.
Length 4 4 Length, in bytes, of the entire DSDT (including the header).
Revision 1 8 2. This field also sets the global integer width for the AML
interpreter. Values less than two will cause the interpreter to use
32-bit integers and math. Values of two and greater will cause the
interpreter to use full 64-bit integers and math.
Checksum 1 9 Entire table must sum to zero.
OEMID 6 10 OEM ID
OEM Table ID 8 16 The manufacture model ID.
OEM Revision 4 24 OEM revision of DSDT for supplied OEM Table ID.
136 April, 2015 Version 6.0