Advanced Configuration and Power Interface Specification

ACPI Source Language (ASL)Reference
of an ASL compiler.
ASL statements declare objects. Each object has three parts, two of which might not be present.
Object := ObjectType FixedList VariableList
FixedList refers to a list, of known length, that supplies data that all instances of a given
ObjectType must have. A fixed list is written as ( a , b , c , … ) where the number of arguments
depends on the specific ObjectType, and some elements can be nested objects, that is (a, b, (q, r, s,
t), d). Arguments to a FixedList can have default values, in which case they can be skipped. Thus,
(a,,c) will cause the default value for the second argument to be used. Some ObjectTypes can have
a null FixedList, which is simply omitted. Trailing arguments of some object types can be left out of
a fixed list, in which case the default value is used.
VariableList refers to a list, not of predetermined length, of child objects that help define the parent.
It is written as { x, y, z, aa, bb, cc } where any argument can be a nested object. ObjectType
determines what terms are legal elements of the VariableList. Some ObjectTypes may have a null
variable list, which is simply omitted.
Other rules for writing ASL statements are the following:
• Multiple blanks are the same as one. Blank, (, ), ‘,’ and newline are all token separators.
• // marks the beginning of a comment, which continues from the // to the end of the line.
• /* marks the beginning of a comment, which continues from the /* to the next */.
• “” (quotes) surround an ASCII string.
• Numeric constants can be written in three ways: ordinary decimal, octal (using 0ddd) or
hexadecimal, using the notation 0xdd.
• Nothing indicates an empty item. For example, { Nothing } is equivalent to {}.
19.2.1 ASL Grammar Notation
The notation used to express the ASL grammar is specified in the following table.
Table 19-350 ASL Grammar Notation
Notation Convention Description Example
Term := Term Term … The term to the left of := can be
expanded into the sequence of
terms on the right.
aterm := bterm cterm means that aterm can be
expanded into the two-term sequence of bterm
followed by cterm.
Angle brackets (< > ) Used to group items. | means either
a b or c d.
Arrow (=>)
Indicates required run-time
reduction of an ASL argument
to an AML data type. Means
“reduces to” or “evaluates to”
at run-time.
“TermArg => Integer” means that the argument
must be an ASL TermArg that must resolve to an
Integer data type when it is evaluated by an AML
interpreter.
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