FIC A360 - Manual (Page 86)

Software Functional Overview
FIC A360 Service Manual
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Active, Passive, and Critical Policies
There are three primary cooling policies that the OS uses to control the thermal state of the
hardware. The policies are Active, Passive and Critical:
− Passive cooling: The OS reduces the power consumption of the system to reduce the
thermal output of the machine by slowing the processor clock. The _PSV control
method is used to declare the temperature to start passive cooling.
− Active cooling: The OS takes a direct action such as turning on a fan. The _ACx
control methods declare the temperatures to start different active cooling levels.
− Critical trip point: This is the threshold temperature at which the OS performs an
orderly, but critical, shut down of the system. The _CRT object declares the critical
temperature at which the OS must perform a critical shutdown.
When a thermal zone appears, the OS runs control methods to retrieve the three temperature
points at which it executes the cooling policy. When the OS receives a thermal SCI it will run
the _TMP control method, which returns the current temperature of the thermal zone. The OS
checks the current temperature against the thermal event temperatures. If _TMP is greater
than or equal to _ACx then the OS will turn on the associated active cooling device(s). If
_TMP is greater than or equal to _PSV then the OS will perform CPU throttling. Finally if
_TMP is greater than or equal to _CRT then the OS will shutdown the system.
An optimally designed system that uses several SCI events can notify the OS of thermal
increase or decrease by raising an interrupt every several degrees. This enables the OS to
anticipate _ACx, PSV, or _CRT events and incorporate heuristics to better manage the
systems temperature.The operating system can request that the hardware change the priority
of active cooling vs passive cooling.
Dynamically Changing Cooling Temperatures
An OEM can reset _ACx and _PSV and notify the OS to reevaluate the control methods to
retrieve the new temperature settings. The following three causes are the primary uses for this
thermal notification:
− When a user changes from one cooling mode to the other.
− When a swappable bay device is inserted or removed. A swappable bay is a slot that
can accommodate several different devices that have identical form factors, such as a
CD-ROM drive, disk drive, and so on. Many mobile PCs have this concept already in
place.
− When the temperature reaches an _ACx or the _PSV policy settings
In each situation, the OEM-provided AML code must execute a Notify ( thermal_zone, 0x80)
statement to request the OS to re-evaluate each policy temperature by running the _PSV and
_ACx control methods.
Resetting Cooling Temperatures from the User Interface
When the user employs the UI to change from one cooling mode to the other, the
following occurs: