Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
9.12 Memory Devices
Memory devices allow a platform to convey dynamic properties of memory to OSPM and are
required when a platform supports the addition or removal of memory while the system is active or
when the platform supports memory bandwidth monitoring and reporting (see Section 9.12.2,
“Memory Bandwidth Monitoring and Reporting). Memory devices may describe exactly the same
physical memory that the System Address Map interfaces describe (see section 14, “System Address
Map Interfaces”). They do not describe how that memory is, or has been, used. If a region of
physical memory is marked in the System Address Map interface as AddressRangeReserved or
AddressRangeNVS and it is also described in a memory device, then it is the responsibility of the
OS to guarantee that the memory device is never disabled.
It is not necessary to describe all memory in the system with memory devices if there is some
memory in the system that is static in nature. If, for instance, the memory that is used for the first 16
MB of system RAM cannot be ejected, inserted, or disabled, that memory may only be represented
by the System Address Map interfaces. But if memory can be ejected, inserted, or disabled, or if the
platform supports memory bandwidth monitoring and reporting, the memory must be represented by
a memory device.
9.12.1 Address Decoding
Memory devices must provide a _CRS object that describes the physical address space that the
memory decodes. If the memory can decode alternative ranges in physical address space, the devices
may also provide _PRS, _SRS and _DIS objects. Other device objects may also apply if the device
can be ejected.
9.12.2 Memory Bandwidth Monitoring and Reporting
During platform operation, an adverse condition external to the platform may arise whose remedy
requires a reduction in the platform’s available memory bandwidth. For example, a server
management controller’s detection of an adverse thermal condition or the need to reduce the total
power consumption of platforms in the data center to stay within acceptable limits. Providing OSPM
with knowledge of a platform induced reduction of memory bandwidth enables OSPM to provide
more robust handling of the condition. The following sections describe objects OSPM uses to
configure platform-based memory bandwidth monitoring and to ascertain available memory
bandwidth when the platform performs memory bandwidth throttling.
9.12.2.1 _MBM (Memory Bandwidth Monitoring Data)
The optional _MBM object provides memory bandwidth monitoring information for the memory
device.
Arguments:
None
Return Value:
A Package containing memory device status information as described in Table 9-261 below
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