trip_points

There are three cooling policies that OSPM uses to control the thermal state of the hardware. The policies are active, passive and critical:

    * Active Cooling. OSPM takes a direct action such as turning on a fan. Active cooling devices typically consume power and produce some amount of noise when enabled (_ON), but are able to cool a thermal zone without limiting system performance. The _ACx objects declare the temperature thresholds OSPM uses to decide when to start or stop different active cooling devices.
    * Passive Cooling. OSPM reduces the power consumption of devices to reduce the temperature of a thermal zone, such as slowing (throttling) the processor clock. Passive cooling devices typically produce no user-noticeable noise. The _PSV control method specifies the temperature threshold where OSPM will start or stop passive cooling.
    * Critical Trip Points. These are threshold temperatures at which OSPM performs an orderly, but critical, shutdown of the system. The _HOT object declares the critical temperature at which OSPM may choose to transition the system into the S4 sleeping state, if supported, The _CRT object declares the critical temperature at which OSPM must perform a critical shutdown. When a thermal zone appears, OSPM runs control methods in the thermal zone to retrieve the temperature thresholds (trip points) at which it executes a cooling policy. When OSPM receives a temperature change notification it will run the _TMP control method, which returns the current temperature of the thermal zone. OSPM checks the current temperature against the temperature thresholds. If _TMP is greater than or equal to _ACx then OSPM will turn on the associated active cooling device(s). If _TMP is greater than or equal to _PSV then OSPM will perform passive cooling. If _TMP is greater than or equal to _HOT then OSPM may choose to transition the system into the S4 sleeping state, if supported. Finally, if _TMP is greater than or equal to _CRT then OSPM will shut the system down. OSPM must also evaluate _TMP when any thermal zone appears in the namespace (for example, during system initialization) and must initiate a cooling policy as warranted independent of receipt of a temperature change notification. This allows OSPM to cool systems containing a thermal zone whose temperature has already exceeded temperature thresholds at initialization time.
      An optimally designed system that uses several thresholds can notify OSPM of thermal increase or decrease by raising an SCI every several degrees. This enables OSPM to anticipate thermal trends and incorporate heuristics to better manage the system's temperature.
      The OS can also request that the platform change the priority of active cooling (performance) versus passive cooling (energy conservation/silence) by invoking the _SCP (Set Cooling Policy) method.
      Note: there _should_ be a hardware shutdown if the values defined by OSPM (read: user) would lead to overheating. Experience shows, that it works on most machines.

Operation     Command