FIC A360 - Manual (Page 89)

Software Functional Overview
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FIC A360 Service Manual
3.5.15 Passive Cooling Equation
Unlike the case for _ACx, during passive cooling the OS takes the initiative to actively
monitor the temperature in order to cool the platform. On an ACPI-compatible platform that
properly implements CPU throttling, the temperature transitions will be similar to the
following figure.
CPU Performance
Time
Temperature
ΔP
_TSP (Sampling period)
100%
50%
T
t
T
n - 1
T
n
Figure 3-4 Temperature and CPU Performance Versus Time
For the OS to assess the optimum CPU performance change required to bring the temperature
down, the following equation must be incorporated into the OS.
ΔP [%] = _TC1 * ( Tn - Tn-1 ) + _TC2 * (Tn - Tt)
where
Tn = current temperature
Tt = target temperature (_PSV)
The two coefficients _TC1 and _TC2 and the sampling period _TSP are hardware-dependent
constants the OEM must supply to the OS (for more information, see section 12.3). The
object _TSP contains a time interval that the OS uses to poll the hardware to sample the
temperature. Whenever _TSP time has elapsed, the OS will run _TMP to sample the current
temperature (shown as Tn in the above equation). Then the OS will use the sampled
temperature and _PSV (which is the target temperature Tt) to evaluate the equation for
ΔP.
The granularity of
ΔP is determined by the CPU duty width of the system. A detailed
explanation of this thermal feedback equation is beyond the scope of this specification.
3.5.16 Critical Shutdown
When the heat reaches the temperature indicated by _CRT, the OS must immediately
shutdown the system. The system must disable the power either after the temperature reaches
some hardware-determined level above _CRT or after a predetermined time has passed.