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Journeyman III

Checking Tctl, ProcHot_L and other thermal functions

As stated in the BIOS and Kernel Developer’s Guide (BKDG) For AMD Family 10h Processors

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

processor’s 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.

Well, I am looking for a relatively simple method, technique, settings or any tool to determine, under some circumstances, when (I mean, for which value of Tctl), these thermal safety functions are actually activated (The processor may take corrective actions that affects performance or operation as a result, such as invoking HTC or THERMTRIP_L).

For a first quick'n'dirty survey I've used some popular tools for Windows OSes (I've used CPU-Z 1.57, RMClock 2.3.5 and Throttle Watch 2.02 to detect any clock changing, and also I used two more tools, Core Temp and SpeedFan, for temperature readings, while I used Mersenne Prime95 to  heat up the CPUs), but for some unknown reason I'm not able to actually detect any change in cores clock frequency, expectedly due to thermal throttle (currently on three AMD 10h CPUs, a Phenom II X4 980, an Athlon II X4 605e, and an Athlon II X3 420e) up to 103° C "reported" core's temperature. So now I think there is some methodological flaw in mine actions.

Please forgive me for my not so good english, and thanks in advance for any hints.

2 Replies
Journeyman III

Is there any piece of code that along with some driver may trap or monitor the CPU's thermal functions activity?


Sorry for the delay.

Here's what I heard from a member of the thermal engineering team:  "The simple answer is: other than Thermtrip (=system shut down) around 125C no other setting is controllable by AMD. Customers can change the settings and make them more graceful through registers not accessible to the end user. They should contact the respective system designer or board manufacturer for guidance on throttling."