Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
system will favor passive cooling (for example, CPU clock throttling). On the other hand, if _AC0 is
less than _PSV the system will favor active cooling (in other words, using the fan). See Figure 11-69
below.
Active Cooling
Preference
Passive Cooling
Preference
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
_CRT
_PSV
_AC0
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
_CRT
_AC0
_PSV
Figure 11-69 Cooling Preferences
The example on the left enables active cooling (for example, turn on a fan) when OSPM detects the
temperature has risen above 50. If for some reason the fan does not reduce the system temperature,
then at 75 OSPM will initiate passive cooling (for example, CPU throttling) while still running the
fan. If the temperature continues to climb, OSPM will quickly shut the system down when the
temperature reaches 90C. The example on the right is similar but the _AC0 and _PSV threshold
values have been swapped to emphasize passive cooling.
The ACPI thermal model allows flexibility in the thermal zone design. An OEM that needs a less
elaborate thermal implementation may consider using only a single threshold (for example, _CRT).
Complex thermal implementations can be modeled using multiple active cooling thresholds and
devices, or through the use of additional thermal zones.
11.2.1 Evaluating Thermal Device Lists
The Notify(thermal_zone, 0x82) statement is used to inform OSPM that a change has been made to
the thermal zone device lists. This thermal event instructs OSPM to re-evaluate the _ALx, _PSL, and
_TZD objects.
For example, a system that supports the dynamic insertions of processors might issue this
notification to inform OSPM of changes to _PSL following the insertion or removal of a processor.
OSPM would re-evaluate all thermal device lists and adjust its policy accordingly.
Notice that this notification can be used with the Notify(thermal_zone, 0x81) statement to inform
OSPM to both re-evaluate all device lists and all thresholds.
602 April, 2015 Version 6.0