Advanced Configuration and Power Interface Specification

ACPI Software Programming Model
5.5.2.4.3 Declaring IPMI Operation Regions
This section describes the Intelligent Platform Management Interface (IPMI) address space and the
use of this address space to communicate with the Baseboard Management Controller (BMC)
hardware from AML.
Similar to SMBus, IPMI operation regions are command based, where each offset within an IPMI
address space represent an IPMI command and response pair. Given this uniqueness, IPMI operation
regions include restrictions on their field definitions and require the use of an IPMI-specific data
buffer for all transactions. The IPMI interface presented in this section is intended for use with any
hardware implementation compatible with the IPMI specification, regardless of the system interface
type.
Support of the IPMI generic address space by ACPI-compatible operating systems is optional, and is
contingent on the existence of an ACPI IPMI device, i.e. a device with the “IPI0001” plug and play
ID. If present, OSPM should load the necessary driver software based on the system interface type as
specified by the _IFT (IPMI Interface Type) control method under the device, and register handlers
for accesses into the IPMI operation region space.
For more information, refer to the IPMI specification.
Each IPMI operation region definition identifies a single IPMI network function. Operation regions
are defined only for those IPMI network functions that need to be accessed from AML. As with
other regions, IPMI operation regions are only accessible via the Field term (see Section 5.5.2.4.3.1,
“Declaring IPMI Fields”).
This interface models each IPMI network function as having a 256-byte linear address range. Each
byte offset within this range corresponds to a single command value (for example, byte offset 0xC1
equates to command value 0xC1), with a maximum of 256 command values. By doing this, IPMI
address spaces appear linear and can be processed in a manner similar to the other address space
types.
The syntax for the OperationRegion term (from Section 19.6.97, “OperationRegion (Declare
Operation Region]”) is described below.
OperationRegion (
RegionName,
RegionSpace,
Offset,
Length
)
Where:
// NameString
// RegionSpaceKeyword
// TermArg=>Integer
// TermArg=>Integer
• RegionName specifies a name for this IPMI network function (for example, “POWR”).
• RegionSpace must be set to IPMI (operation region type value 0x07).
• Offset is a word-sized value specifying the network function and initial command value offset
for the target device. The network function address is stored in the high byte and the command
value offset is stored in the low byte. For example, the value 0x3000 would be used for a device
with the network function of 0x06, and an initial command value offset of zero (0).
• Length is set to the 0x100 (256), representing the maximum number of possible command
values, for regions with an initial command value offset of zero (0). The difference of these two
values is used for regions with non-zero offsets. For example, a region with an Offset value of
0x3010 would have a corresponding Length of 0xF0 (0x100 minus 0x10).
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