FIC A360 User Manual

 

Software Functional Overview 

 
3-32 

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

 

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.