Advanced Configuration and Power Interface Specification

Device Configuration
Note: If the machine does not support PNPBIOS, this object is not required.
6.5.4 _REG (Region)
The OS runs _REG control methods to inform AML code of a change in the availability of an
operation region. When an operation region handler is unavailable, AML cannot access data fields in
that region. (Operation region writes will be ignored and reads will return indeterminate data.).
Arguments: (2)
Arg0 – An Integer containing the Operation Region address space ID
Arg1 – An Integer containing the handler connection code
0 – disconnect the handler
1 – connect the handler
Return Value:
None
Valid Operation Region address space IDs:
0 – SystemMemory
1 – SystemIO
2 – PCI_Config
3 – Embedded Controller
4 – SMBus
5 – SystemCMOS
6 – PCIBARTarget
7 – IPMI
8 - GeneralPurposeIO
9 - GenericSerialBus
0x0A-0x7F –Reserved
0x80-0xFF –OEM (custom) region space
Except for the cases shown below, control methods must assume all operation regions inaccessible
until the _REG(RegionSpace, 1) method is executed. Once _REG has been executed for a particular
operation region, indicating that the operation region handler is ready, a control method can access
fields in the operation region. Conversely, control methods must not access fields in operation
regions when _REG method execution has not indicated that the operation region handler is ready.
For example, until the Embedded Controller driver is ready, the control methods cannot access the
Embedded Controller. Once OSPM has run _REG(EmbeddedControl, 1), the control methods can
then access operation regions in Embedded Controller address space. Furthermore, if OSPM
executes _REG(EmbeddedControl, 0), control methods must stop accessing operation regions in the
Embedded Controller address space.
The exceptions for this rule are:
1. OSPM must guarantee that the following operation regions must always be accessible:
• PCI_Config operation regions on a PCI root bus containing a _BBN object.
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