Dedicated to Energy Savings
To design dedicated low power x86 devices on the board level, there are three possible alternatives: redesign a standard board, develop a dedicated board from scratch, or use a Computer-on-Modules-based design with only the application-specific components on the carrier board, for lower costs, better time-to-market and optimized energy consumption. But this is not the only consideration. Engineers must also optimize power distribution and make efficient use of energy saving capabilities. The more energy saving functionalities the board vendor supports, the easier it will be to design the low power system. There are only two restrictions to creating true low power devices: the application’s needs and development costs respectively time.
The challenge starts with the specification
For 80 to 90% of devices, the application defines the class of system required in regards of CPU performance, chipset features and additional components/devices. Nevertheless, using latest processor and chipset technology is the easiest step to improve energy efficiency: Over the years, reduced structure size for CPU and chipset as well as the move from singlecore to multicore architectures, multiplied the performance per watt ratio for high performance devices. With the 45 nm Intel Atom processor, embedded computer technology now gains the same improvements for low power designs: It features for the first time an overall reduced power consumption, besides a dramatically improved performance per watt ratio. Compared to previous Intel Pentium M based designs, Intel Atom devices feature half the energy consumption at a comparable performance.
Better energy efficiency with SFF designs
If the application considerations allow to use an off-the-shelf embedded board design with Small Form Factor technology; this would be the fastest and easiest solution for a low power design. For instance, Intel offers the current Core 2 Duo processors also in a Small Form Factor version with reduced package size. In comparison to the standard version, the SFF features a much lower thermal design power (TDP). A next step in cutting down energy consumption would be to create a customized version of the standard board, reducing interfaces and components to the required minimum. Maximum effort and highest design flexibility would be to a full custom design. But what to do, when it comes to time-to-market and costs? Computer-on-Modules design can offer the best of two worlds.
Semi-custom designs with Computer-on-Modules
Designs with Computer-on-Modules not only feature the ability to implement only the interfaces that are needed for the specific application via the individual carrier board design, but they also offer shorter development times and therefore faster time-to-market and a higher cost efficiency due to the fact that the computing core is a COTS product. Consequently, engineers can concentrate their efforts on the carrier board design. One Computer-on-Modules standard that is especially compelling in this regard is COM Express.
Optimized power distribution
Along with the proper choice of a suitable Computer-on-Module standard, the quality of the power distribution is an additional factor in an economic design. For instance, depending on the application, up to eight or more different voltages must be generated from the basic supply voltage, resulting in unavoidable power losses. Therefore, COM Express Computer-on-Modules with a wide range power supply, e.g., from 8.5V to 18V, help to improve power efficiency in the systems power distribution. Using such modules it is not necessary to generate additional voltages or to implement an additional power supply. For mobile or battery-powered applications, developers can also experience great difficulties when they have to implement a battery-based power supply. Some vendors offer a Smart Battery concept and ready-to-use schematics for those applications. The schematics are free to modify which can help to dramatically improve power efficiency.
Efficient use of sleep states
Another important energy-saving function is the comprehensive implementation of sleep states for the time that the COM is idling. Ideally, the COM should feature a Suspend to RAM (S3) mode that provides only the minimum voltage needed to keep the contents of the RAM intact. In this state, all other components should be powered off and the entire unit should only be supplied from the suspend voltage of the power supply. By utilizing this feature, quiescent current can be minimized and, therefore, power losses that would occur if the power supply remained in full operation can be avoided. Developers should, therefore, take care, that both, power distribution as well as ACPI (Advanced Computing and Power Interface) functions for Suspend to RAM are implemented properly in the COM and carrierboard. Additionally, even the S5 state (power off) offers energy saving abilities, e.g., for applications that make use of wake-on-lan (WoL) capabilities. When WoL is not required, e.g. in most mobile applications, the S5 Eco state, reduces the module’s power consumption to less than 1 mA, which equals a reduction by at least a factor of 200 compared to the regular S5 state. Via BIOS, the either S5 or the S5 Eco state can be selected at full software compatibility. When S5 Eco is activated it also disconnects the 5V Stand-by Supply and turns off the chipset to dramatically improve power consumption. The module has to be actived via the standard power button or other external circuits on the carrier board.
Consequently, the S5 Eco is excellent for battery-powered systems which need to support ACPI stated. Additionally, with respects to the Ecodesign Directive (2005/32/EC) that provides consistent EU-wide rules for improving the environmental performance of energy-using products (EUPs) through ecodesign, the S5 Eco eases realization of these regulations.
Software as another decisive factor
But hardware isn’t the only potential energy saver. Software can also take a great part in saving energy by the intelligent use of power status information, e.g. for throttling processor speed or switching off unneeded components. For this it is essential that the COM manufacturer provides software support for the energy saving features of the hardware, so that OEM-development can be facilitated and roll out times can be shortened.
When considering the best x86 system design in terms of energy efficiency for an application, developers should take into account that cutting-edge energy savings can usually not be accomplished by the use of standard products, but only with custom or semi-custom designs. Computers-on-Modules are a good way to work on energy savings by limiting system features to only the application specific components and interfaces and by the use of established design guides. Developers should also take a closer look at how energy-saving potentials are implemented, e.g., through optimized power distribution, highly integrated components, and the integration of ACPI-functionalities for sleep and power-off states. Since energy saving doesn’t end at the hardware-level but is also affected by the software and especially the software’s control of the energy functionalities implemented in the hardware, the supply of building blocks and management tools by the hardware manufacturer, such as battery management systems, code samples, board support packages, etc., should also be taken under consideration.