Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
FieldUnitList is a variable-length list of individual field unit definitions, separated by commas. Each
entry in the field unit list is one of the following:
Table 19-367 Field Unit list entires
FieldUnitName, BitLength
Offset (ByteOffset)
AccessAs (AccessType, AccessAttribute)
Connection (ConnectionResourceObj)
FieldUnitName is the ACPI name for the field unit (1 to 4 characters), and BitLength is the length of
the field unit in bits. Offset is used to specify the byte offset of the next defined field unit. This can
be used instead of defining the bit lengths that need to be skipped. AccessAs is used to define the
access type and attributes for the remaining field units within the list. Connection is used to identify
the connection resource of the field access. This is necessary for GenericSerialBus and
GeneralPurposeIO operation region types only.
Description
Declares a series of named data objects whose data values are fields within a larger object. The fields
are parts of the object named by RegionName, but their names appear in the same scope as the Field
term.
For example, the field operator allows a larger operation region that represents a hardware register to
be broken down into individual bit fields that can then be accessed by the bit field names. Extracting
and combining the component field from its parent is done automatically when the field is accessed.
When reading from a FieldUnit, returned values are normalized (shifted and masked to the proper
length.) The data type of an individual FieldUnit can be either a Buffer or an Integer, depending on
the bit length of the FieldUnit. If the FieldUnit is smaller than or equal to the size of an Integer (in
bits), it will be treated as an Integer. If the FieldUnit is larger than the size of an Integer, it will be
treated as a Buffer. The size of an Integer is indicated by the DSDT header’s Revision field. A
revision 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. For more information about data types and FieldUnit
type conversion rules, see Section 19.3.5.7, “Data Type Conversion Rules”.
Accessing the contents of a field data object provides access to the corresponding field within the
parent object. If the parent object supports Mutex synchronization, accesses to modify the
component data objects will acquire and release ownership of the parent object around the
modification.
The following table relates region types declared with an OperationRegion term to the different
access types supported for each region.
Table 19-368 OperationRegion Region Types and Access Types
Region Type Permitted Access Type(s) Description
SystemMemory ByteAcc, WordAcc, DWordAcc, All access allowed
QWordAcc, or AnyAcc
838 April, 2015 Version 6.0