Advanced Configuration and Power Interface Specification

ACPI Software Programming Model
accesses using the data element name. An Operation Region is a specific region of operation within
an address space that is declared as a subset of the entire address space using a starting address
(offset) and a length (see Section 19.6.97 “OperationRegion (Declare Operation Region)”). Control
methods must have exclusive access to any address accessed via fields declared in Operation
Regions. Control methods may not directly access any other hardware registers, including the ACPIdefined
register blocks. Some of the ACPI registers, in the defined ACPI registers blocks, are
maintained on behalf of control method execution. For example, the GPEx_BLK is not directly
accessed by a control method but is used to provide an extensible interrupt handling model for
control method invocation.
Note: Accessing an OpRegion may block, even if the OpRegion is not protected by a mutex. For
example, because of the slow nature of the embedded controller, an embedded controller
OpRegion field access may block.
There are eight predefined Operation Region types specified by ACPI as described in Table 5-137.
Table 5-137 Operation Region Address Space Identifiers
Name (RegionSpace Keyword)
Value
SystemMemory 0
SystemIO 1
PCI_Config 2
EmbeddedControl 3
SMBus 4
SystemCMOS 5
PCIBARTarget 6
IPMI 7
GeneralPurposeIO 8
GenericSerialBus 9
Reserved
0x0A-0x7F
In addition, OEMs may define Operation Regions Address Space ID types 0x80 to 0xFF.
Operation region access to the SystemMemory, SystemIO, and PCI_Config address spaces is simple
and straightforward. Operation region access to the EmbeddedControl address space is described in
Section 12, “ACPI Embedded Controller Interface Specification”. Operation region access to the
SMBus address space is described in Section 13, “ACPI System Management Bus Interface
Specification”. Operation region access to the CMOS, PCIBARTarget, IPMI, GenericSerialBus and
GeneralPurposeIO address spaces is described in the following sections.
5.5.2.4.1 CMOS Protocols
This section describes how CMOS battery-backed non-volatile memory can be accessed from ASL.
Most computers contain an RTC/CMOS device that can be represented as a linear array of bytes of
non-volatile memory. There is a standard mechanism for accessing the first 64 bytes of non-volatile
RAM in devices that are compatible with the Motorola RTC/CMOS device used in the original IBM
PC/AT. Existing RTC/CMOS devices typically contain more than 64 bytes of non-volatile RAM,
and no standard mechanism exists for access to this additional storage area. To provide access to all
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