User Guide XB1 COM Express Module
Thermal Considerations
In order to avoid malfunctioning of the XB1 COM Express Module, take care of appropriate cooling of the processor and system, e.g. by a cooling fan suitable to the maximum power consumption of the CPU chip actually in use. Please note, that the processors temperature is steadily measured by a special controller (LM87), attached to the onboard SMBus® (System Management Bus). A second temperature sensor internal to the LM87 allows for acquisition of the boards surface temperature. Beside this the LM87 also monitors most of the supply voltages. A suitable software to display both, the temperatures as well as the supply voltages, is MBM (Motherboard Monitor), which can be downloaded from the web. After installation, both temperatures and voltages can be observed permanently from the Windows taskbar.
The XB1 COM Express Module is equipped with a passive heatsink
The table showing the supported processors above give also the maximum power consumption (TDP
=Thermal Design Power) of a particular processor. Fortunately, the power consumption is by far lower when executing typical Windows or Linux tasks. The heat dissipation may increase considerably when e.g. rendering software such as the Acrobat Distiller is executed.
The Pentium M processors support Intel's Enhanced SpeedStep® technology. This enables dynamic switching between multiple core voltages and frequencies depending on core temperature and currently required performance. The processors are able to reduce their core speed and core voltage in up to 8 steps down to 600MHz. This leads to an obvious reduction of power consumption (max. 7.5W @600MHz) resulting in less heating. This mode of lowering the processor core temperature is called TM2 (TM=Thermal Monitor). Note, that TM2 is not supported by Celeron M processors.
Another way to reduce power consumption is to modulate the processor clock. This mode (TM1) is supported also by the Celeron M processors and is achieved by actuating the 'Stop Clock' input of the CPU. A throttling of 50% e.g. means a duty cycle of 50% on the stop clock input. However, while saving considerable power consumption, the data throughput of the processor is also reduced. The processor works at full speed until the core temperature reaches a critical value. Then the processor is throttled by 50%. As soon as the high temperature situation disappears the throttling will be disabled and the processors runs at full speed again.
A similar feature is embedded within the Graphics and Memory Controller (GMCH) i915GM. An on- die temperature sensor is used to protect the GMCH from exceeding its maximum junction temperature (TJ,max=105°C) by reducing the memory bandwidth.
These features are controllable by BIOS menu entries. By default the BIOS of the XB1 COM Express Module enables mode TM2 which is the most efficient.
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