2.10 Thermal Functions
Thermal functions HTC, STC and THERMTRIP are intended to maintain processors temperature in a valid
range by:
Providing an input to the external circuitry that controls cooling.
Lowering power consumption by switching to lower-performance P-state or.
Sending processor to the THERMTRIP state to prevent it from damage.
The processor thermal-related circuitry includes (1) the temperature calculation circuit (TCC) for determining
the temperature of the processor and (2) logic that uses the temperature from the TCC. The processor includes
a thermal diode as well.
2.10.1 The Tctl Temperature Scale
Tctl is the processor temperature control value, used by the platform to control cooling systems. Tctl is accessible through SB-TSI and F3xA4[CurTmp]. Tctl is a non-physical temperature on an arbitrary scale measured in degrees. It does
not represent an actual physical temperature like die or case temperature. Instead, it specifies the processor temperature relative to the point at which the system must supply the maximum cooling for the processors specified maximum case temperature and maximum thermal power dissipation. It is defined as follows for all parts:
For Tctl = 0 to Tctl_max - 0.125: the temperature of the part is [Tctl_max - Tctl] degrees under the temperature for which maximum cooling is required.
For Tctl = Tctl_max to 255.875: the temperature of the part is [Tctl - Tctl_max] degrees over the worst-case expected temperature under normal conditions. The processor may take corrective actions that affects performance or operation as a result, such as invoking HTC or THERMTRIP_L.
2.10.2 Thermal Diode
The thermal diode is a diode connected to the THERMDA and THERMDC pins used for thermal measurements.
External devices use measurements from the thermal diode measurements to calculate temperature during operation and test. These measurements are required to be adjusted as specified by F3xE4[DiodeOffset].
This diode offset supports temperature sensors using two sourcing currents only. Other sourcing current implementations are not compatible with the diode offset and are not supported. A correction to the offset may be required for temperature sensors using other current sourcing methods. Contact the temperature sensor vendor to determine whether an offset correction is needed.
2.10.3 Temperature-Driven Logic
The temperature calculated by the TCC is used by HTC, STC, THERMTRIP, the PROCHOT signal.
2.10.3.1 PROCHOT_L and Hardware Thermal Control (HTC)
The processor HTC-active state is characterized by (1) the assertion of PROCHOT_L, (2) reduced power consumption, and (3) reduced performance. While in the HTC-active state, the processor reduces power consumption by limiting all CPU cores to a P-state (specified by F3x64[HtcPstateLimit]). See section 2.4.2 [P-states] on page 31. While in the HTC-active state, software should not change F3x64 (except for HtcActSts and HtcEn).
Any change to the previous list of fields when in the HTC-active state can result in undefined behavior. HTC status and control is provided through F3x64.
The PROCHOT_L pin acts as both an input and as an open-drain output. As an output, PROCHOT_L is driven low to indicate that the HTC-active state has been entered due to an internal condition, as described by the following text. The minimum assertion and deassertion time for PROCHOT_L is 15 ns.
The processor enters the HTC-active state if all of the following conditions are true:
F3xE8[HtcCapable]=1
F3x64[HtcEn]=1
PWROK=1
THERMTRIP_L=1
The processor is not in the C3 ACPI state.
and any of the following conditions are true:
Tctl is greater than or equal to the HTC temperature limit (F3x64[HtcTmpLmt]).
PROCHOT_L=0
The processor exits the HTC-active state when all of the following are true:
Tctl is less than the HTC temperature limit (F3x64[HtcTmpLmt]).
Tctl has become less than the HTC temperature limit (F3x64[HtcTmpLmt]) minus the HTC hysteresis limit (F3x64[HtcHystLmt]) since being greater than or equal to the HTC temperature limit (F3x64[HtcTmpLmt]).
PROCHOT_L=1.
The default value of the HTC temperature threshold (Tctl_max) is specified in the Power and Thermal Datasheet.
2.10.3.2 Software Thermal Control (STC)
STC is controlled by [The Software Thermal Control (STC) Register] F3x68. This register provides a software-controlled mechanism to alter power consumption based on temperature. When the processor control temperature (Tctl; see section 2.10.1 [The Tctl Temperature Scale] on page 110) exceeds the temperature threshold specified by F3x68[StcTmpLmt], then the processor enters the STC thermal zone. When it subsequently drops below F3x68[StcTmpLmt] minus F3x68[StcHystLmt], the processor exits the STC thermal zone. F3x68 controls whether interrupts or special bus cycles (which may be converted into interrupts by the chipset) are generated when the processor transitions into and out of the STC thermal zone. The interrupt handler may take an action to alter power consumption or alter the level of external cooling.
One way that software may reduce power is to program the processor to enter the STC-active state. This is like the HTC-active state, however PROCHOT_L is not asserted. The processor enters the STC-active state if F3x68[StcPstateEn]=1. While in the STC-active state, the processor limits the performance to the P-state specified by [The Software Thermal Control (STC) Register] F3x68[StcPstateLimit]; See section 2.4.2 [P-states]
on page 31.
2.10.3.3 THERMTRIP
If the processor supports the THERMTRIP state (as specified by [The Thermtrip Status Register] F3xE4[ThermtpEn] or CPUID Fn8000_0007[TTP], which are the same) and the temperature approaches the point at which the processor may be damaged, the processor enters the THERMTRIP state. The THERMTRIP function is enabled after cold reset (after PWROK asserts and RESET_L deasserts). It remains enabled in all other processor states, except during warm reset (while RESET_L is asserted). The THERMTRIP state is characterized as follows:
The THERMTRIP_L signal is asserted.
Nearly all clocks are gated off to reduce dynamic power.
A low-value VID is generated.
In addition, the external chipset is expected to place the system into the S5 ACPI state (power off) if THERMTRIP_L is detected to be asserted.
A cold reset is required to exit the THERMTRIP state.
Bookmarks