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Last Update:
July 2006

ThermalControl

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Get a grip on thermal control

ThermalControl lets you monitor and manipulate the thermal control mechanisms of Pentium 4, Pentium M and Xeon processors. You can check if the die temperature is within recommended specifications and you can determine what measures the processor should take when the temperature exceeds the specifications. You can use ThermalControl to boost the CPUs performance (we’ve measured an increase of up to 30%) by deactivating thermally controlled throttling mechanisms or you can reduce the processors power consumption to extend battery life or reduce fan noise.


Features

1. Enable Thermal Monitor 1, Thermal Monitor 2 or neither

Both thermal monitoring mechanisms reduce power consumption and cool the processor by slowing it down. They’re engaged when the temperature measured by an on die thermal diode exceeds a given threshold. The reason for this occurring is a cooling solution that’s under dimensioned for the power dissipation of the processor.

If the processor is being throttled by one of the thermal monitoring mechanisms, disabling thermal monitoring can significantly boost the performance of the processor – we have measured a 30 percent increase. The downside: it also may reduce the lifespan of the processor. ThermalControl simply offers you a choice – if you need the highest performance your CPU has to offer you can disable the throttling mechanisms.

If your priority is not to operate the processor with highest performance but within its thermal specifications, you might have to pick from several options. If your processor supports Thermal Monitor 1 and Thermal Monitor 2, then generally activating Thermal Monitor 2 is the best choice, because it achieves a larger reduction in the power consumption with less impact on performance than Thermal Monitor 1.

But there is an exception to this rule: If your processor supports Enhanced SpeedStep in addition and you are using an operating system like Windows XP, the safest way to prevent overheating may be by activating Thermal Monitor 1 and Enhanced SpeedStep. Enhanced SpeedStep works in much the same way as Thermal Monitor 2, except that it’s controlled by the software (i.e. the operating system) instead of by a thermal diode. The data that Windows XP uses to control Enhanced SpeedStep is (among other things) the CPU temperature. In fact, if you select the power policy “Always On” in the “Power Options” of the Windows XP Control Panel, a high CPU temperature is the only reason for which Windows will throttle the CPU with Enhanced SpeedStep. So, in essence, Windows XP combined with Enhanced SpeedStep acts very similar to Thermal Monitor 2. In this scenario Thermal Monitor 1 serves as an additional safety mechanism – if required both Enhanced SpeedStep and Thermal Monitor 1 can work together and if Enhanced SpedStep should fail, Thermal Monitor 1 remains as a fallback mechanism.

2. Monitor thermal status

Symbols show if the die temperature is currently above its temperature limit (around 100° Celsius) or if it was in the past. ThermalControl can run in the background, displaying the temperature symbols in the system tray area.

3. Use on demand clock modulation

Use this to reduce power consumption and cool the processor by slowing it down. The percentage values offered by ThermalControl correspond to the duty cycle (the fraction of time for which the clock signal is active). You can use this mechanism to create a very low power and silent PC (the lower the power dissipation, the less noisy ventilation is required for cooling).

4. Enhanced SpeedStep

This mechanism allows software (the operating system) to control the voltage and clock frequency of the processor. If your processor supports Enhanced SpeedStep, you can enable or disable this feature and the current operating point will be displayed. Our experience is that in many CPUs this function is hard wired and can not be disabled.

5. View information on the CPU

You’ll find the actual CPU clock frequency updated in nearly-real-time, the CPU brand string (if available), the processor family, type, model and stepping as well as the revision of the currently loaded microcode update.

6. Control from the command line

Most functions of ThermalControl can be used via command line arguments, so you can automatically load your favourite configuration at boot time or create profiles for specific tasks.


Requirements

Windows 2000, XP or Server 2003 (32-Bit versions)

Pentium 4, Pentium M or Xeon processor

Administrator privileges


Thermal basics

For years Intels primary design goal was to introduce processors with ever higher clock speeds. It was a marketing approach: High GHz numbers were easily sold as an equivalent to high performance. One consequence of this strategy is that many of us now have CPUs in our PCs that use over 100 Watts of power. 100 Watts is a lot – as a comparison, think of a 100 Watt light bulb. They get really hot, because most of the consumed power is dissipated as heat. It’s the same principle with processors, only that they have to be kept relatively cool. So in addition to using a lot of power (and possibly reducing battery life) you also need high performance cooling solutions which generally use noisy fans to shovel hot air away from the CPU.

At the heart of the issue are three equations:

I) P = C V2F

This is Ohm’s Law (P=power, C=capacitance, V=voltage and F=frequency). Put in easy terms it means that the power consumption of the processor increases proportionally to the operating frequency and with the square of the operating voltage.

II) ∂S/∂F > 0

This means, that the computational speed S of the processor increases with its operating frequency.

III) ∂V/∂F > 0

The voltage required to operate the processor increases with its operating frequency.

Conclusion

Put it all together and you learn the obvious: If you lower the operating frequency you can lower the voltage accordingly. This saves power but also slows down the processor.


Thermal control mechanisms

To help handle the power and associated heat and noise problems, Intel equipped its Pentium 4, Pentium M and Xeon processors with a number of features that control and monitor the temperature and power consumption.


1. Catastrophic shutdown mechanism

Introduced with the P6 family processors and also implemented in Pentium 4, Pentium M and Xeon processors. This mechanism is not visible to software and is always enabled. When an on die thermal diode measures an elevated die temperature (around 125° Celsius), the processor will automatically shut down and the FSB signal THERMTRIP# will go active and stay active.

2. Thermal Monitor 1 & 2

Software can enable Thermal Monitor 1, Thermal Monitor 2 or neither. For the processor to be operating within specification Intel requires one of these mechanisms to be enabled. When an on die thermal diode measures a temperature that exceeds the processors recommended operating temperature, the selected mechanism is set active and the PROCHOT# signal is asserted. The trip temperature is around 100° Celsius and neither configurable by nor visible to software. The PROCHOT# signal is bi-directional, so that it can also be used to activate the thermal control mechanisms from an external source. Once the temperature has dropped below the threshold the selected mechanism is deactivated after a small amount of hysteresis.

2a. Thermal Monitor 1

This mechanism is present in Pentium 4, Pentium M and Xeon processors. When Thermal Monitor 1 is activated, the processor clock will be modulated by alternately turning the clock off an on. The fraction of time for which the clock is activated is called duty cycle. A duty cycle of 40% means the clock is active for 40% of the time and inactive for the remaining 60%. The duty cycle depends on the processor and is typically 30-50% when Thermal Monitor 1 is active.

2b. Thermal Monitor 2

This mechanism is present in all Pentium M and newer Pentium 4 and Xeon processors. When Thermal Monitor 2 is activated, the processor will lower its clock frequency (FID) and input voltage (VID). Software must select the new operating point (frequency and voltage) from a processor specific set of values.

3. On demand clock modulation

This mechanism is present in all Pentium 4, Pentium M and Xeon processors. On demand clock modulation works in the same way as Thermal Monitor 1, except that it is completely software controlled. When activated, the processor clock will be modulated by alternately turning the clock off and on. The duty cycle (the fraction of time for which the clock is activated) is selectable by software, possible values range from 12.5% to 87.5%.

4. Enhanced SpeedStep

This mechanism is present in all Pentium M and newer Pentium 4 and Xeon processors. Enhanced SpeedStep works in the same way as Thermal Monitor 2, except that it is completely software controlled. When activated, Software must select the new operating point (frequency and voltage) from a processor specific set of values.

5. Thermal diode

All Pentium 4, Pentium M and Xeon processors have a second on die thermal diode that is not visible to software. Its signal (THERMDA, THERMDC) can be read by an off-die analog/digital converter usually located on the motherboard. Reading of the thermal diode signal will not necessarily reflect the temperature of the hottest location on the die. This is mainly due to inaccuracies of the sensor and on-die thermal gradients.

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