Thermal management is another fundamental capability of all mobile platforms. Managing the platform thermals enables us to maximize CPU and platform performance within thermal constraints. Thermal management also improves ergonomics with a cooler system and lower fan acoustic noise.

In order to better control the thermal conditions of the system, the Intel^® Core™ Duo processor presents two new concepts: the use of digital sensors for high accuracy die temperature measurements and dual-core multiple-level thermal control.

In the previous Pentium^® M processor, a single analog thermal diode was used to measure die temperature. Thermal diode cannot be located at the hottest spot of the die and therefore some offset was applied to keep the CPU within specifications. For these systems it was sufficient, since the die had a single hot spot. In the Intel Core Duo processor, there are several hot spots that change position as a function of the combined workload of both cores. Figure 8 shows the differences between the use of the traditional analog sensor and the use of the new digital sensors.

Figure 8: Analog vs. digital sensors in Intel Core Duo processors
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As we can see the use of multiple sensing points provides high accuracy and close proximity to the hot spot at any time. An analog thermal diode is still available on the Intel Core Duo processor. The use of a digital thermometer allows tighter thermal control functions, allowing higher performance in the same form factor. The improved capability also allows us to achieve better ergonomic systems that do not get too hot, can operate more quietly, and are more reliable. Unlike diode-based thermal management algorithms that require some temperature guard band (or activating the self throttle mechanism as a safety-net), the digital thermometer is tested and calibrated against specifications. Full functionality and reliability of the processor are guaranteed, as long as the reported temperature is equal to or below the maximum specified temperature. Any inaccuracy or offset are programmed into the device and already accounted for.

The thermal measurement function provides interfaces to power-management software such as the industry-standard ACPI. Each core can be defined as an independent thermal zone, or a single thermal zone for the entire chip. The maximum temperature for each thermal zone is reported separately via dedicated registers that can be polled by the software.

In addition to the polling capability, the digital thermometer implements event-based reporting. Control software programs temperature thresholds that require actions. Such actions can be fan activation or passive control policy such as dynamic voltage and frequency scaling. Upon temperature crossing of the threshold, an APIC-defined interrupt is generated and it initiates the requested action.

Intel Core Duo technology implemented a dual-core power monitor capability. Power monitor functionality is provided in order to prevent thermal exceptions, and it can throttle the CPU once the temperature exceeds specifications. The overview of the power monitoring logic is described in Figure 9.

Figure 9: Thermal control overview
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The power monitor continuously tracks the die temperature. If the temperature reaches the maximum allowed value, a throttle mechanism is initiated. A multi-level tracking algorithm is implemented. Throttling starts with the more efficient dynamic voltage scaling policy and if not sufficient, the power monitor algorithm continues lowering the frequency. If an extreme cooling malfunction occurs, an Out of Spec notification will be initiated, requesting controlled shutdown. Lastly, the CPU can initiate a thermal shutdown and turn off the system.

Power and thermal management activities in notebook computers are usually performed by the OS and platform control functions. These thermal management features are designed to best serve user preferences under notebook constraint conditions. Thermal monitor function is not expected to be activated under these normal operation conditions. The thermal monitor mechanism ensures that the CPU will never exceed the CPU-specified parameters and guarantees functionality and reliability at any time.

The use of high accuracy temperature reading together with thermal monitoring protection enables high performance in thermally limited form factors, while allowing improved ergonomics and high reliability.