Advanced Configuration and Power Interface Specification

ACPI Source Language (ASL)Reference
19.3.5.7 Data Type Conversion Rules
The following table presents the detailed data conversion rules for each of the allowable data type
conversions. These conversion rules are implemented by the AML Interpreter and apply to all
conversion types — explicit conversions, implicit source conversions, and implicit result
conversions.
Table 19-357 Object Conversion Rules
To convert
from an
object of this
Data Type
To an object
of this Data
Type
This action is performed by the AML Interpreter:
Buffer Buffer Field The contents of the buffer are copied to the Buffer Field. If the buffer is
smaller than the size of the buffer field, it is zero extended. If the buffer is
larger than the size of the buffer field, the upper bits are truncated.
Compatibility Note: This conversion was first introduced in ACPI 2.0. The
behavior in ACPI 1.0 was undefined.
Buffer Field
DDB Handle
Debug Object
Field Unit
Integer
String
[See the
Integer and
Buffer Rules]
[See the
Integer Rule]
Each buffer byte is displayed as a hexadecimal integer, delimited by
spaces and/or commas.
The entire contents of the buffer are copied to the Field Unit. If the buffer is
larger (in bits) than the size of the Field Unit, it is broken into pieces and
completely written to the Field Unit, lower chunks first. If the buffer (or the
last piece of the buffer, if broken up) is smaller than the size of the Field
Unit, it is zero extended before being written.
If no integer object exists, a new integer is created. The contents of the
buffer are copied to the Integer, starting with the least-significant bit and
continuing until the buffer has been completely copied — up to the
maximum number of bits in an Integer. The size of an Integer is indicated
by the Definition Block table header’s Revision field. A Revision field value
less than 2 indicates that the size of an Integer is 32 bits. A value greater
than or equal to 2 signifies that the size of an Integer is 64 bits. If the buffer
is smaller than the size of an integer, it is zero extended. If the buffer is
larger than the size of an integer, it is truncated. Conversion of a zerolength
buffer to an integer is not allowed.
If no string object exists, a new string is created. If the string already exists,
it is completely overwritten and truncated or extended to accommodate the
converted buffer exactly.The entire contents of the buffer are converted to a
string of two-character hexadecimal numbers, each separated by a space.
A zero-length buffer will be converted to a null (zero-length) string.
If the Buffer Field is smaller than or equal to the size of an Integer (in bits),
it will be treated as an Integer. Otherwise, it will be treated as a Buffer. The
size of an Integer is indicated by the Definition Block table header’s
Revision field. A Revision field value less than 2 indicates that the size of
an Integer is 32 bits. A value greater than or equal to 2 signifies that the
size of an Integer is 64 bits. (See the conversion rules for the Integer and
Buffer data types.)
The object is treated as an Integer (See conversion rules for the Integer
data type.)
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