Advanced Configuration and Power Interface Specification

ACPI Source Language (ASL)Reference
19
ACPI Source Language (ASL)Reference
This section formally defines the ACPI Source Language (ASL). ASL is a source language for
defining ACPI objects including writing ACPI control methods. OEMs and BIOS developers define
objects and write control methods in ASL and then use a translator tool (compiler) to generate ACPI
Machine Language (AML) versions of the control methods. For a formal definition of AML, see the
ACPI Machine Language (AML) Specification, Section 20, “ACPI Machine Language
Specification.”
AML and ASL are different languages though they are closely related.
Every ACPI-compatible OS must support AML. A given user can define some arbitrary source
language (to replace ASL) and write a tool to translate it to AML.
An OEM or BIOS vendor needs to write ASL and be able to single-step AML for debugging.
(Debuggers and similar tools are expected to be AML-level tools, not source-level tools.) An ASL
translator implementer must understand how to read ASL and generate AML. An AML interpreter
author must understand how to execute AML.
This section has two parts:
• The ASL grammar, which is the formal ASL specification and also serves as a quick reference.
• A full ASL reference, which includes for each ASL operator: the operator invocation syntax, the
type of each argument, and a description of the action and use of the operator.
19.1 ASL 2.0 Symbolic Operators and Expressions
For the math and logical operations, ASL supports standard symbolic operators and expressions that
are similar to the C language. Compound assignment operators are also supported. The AML code
that is generated from the symbolic operators and expressions is identical to the AML code
generated for the equivalent legacy ASL operators.
The table below summarizes the ASL 2.0 support for symbolic operators.
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