Computer-on-modules for compact embedded designs

Computer-on-modules for compact embedded designs

For 10 years designers have cut time to market with interchangeable COM boards

BY CHRISTINE VAN DE GRAAF
Kontron, Poway, CA
http://us.kontron.com

Designers of embedded products are constantly asked to think strategically and choose platforms that deliver both longevity and performance. Maximizing the use of engineering resources, cutting development time, reducing total cost of ownership, and getting to market quickly are all part of the demands that have become standard for today’s embedded system engineers.

These demands can be equally as important as the application-specific features of a given design. Computer-on-modules (COMs) are prime candidates for addressing these issues and laying the foundation for continued evolution and application scalability.

Ten years ago, COMs were new to the embedded universe. Today they are recognized for combining portability with performance and flexibility.

The evolution of COM standards

The advantages of COMs have increased steadily with each new standard. The concept started as the credit-card-sized DIMM PC in 1998; two years later the ETX standard was established and included full PC functionality.

The upgrade to ETX 3.0 added SATA connectors while maintaining the same pinout. And as PCI Express ushered in the opportunity for more advanced technologies, a new COM standard was required as ETX could not be modified and retain the same pinout.

Enter COM Express, a PICMG open specification, defined in July 2005 and originally sponsored by Kontron, Intel, PFU, and RadiSys, enabling a smooth transition from PCI, ISA, and IDE to PCI Express, SATA, and other future-focused technologies.

The standard specifies module sizes in basic (ETXexpress) (125 x 95 mm), extended (155 x 110 mm), and compact (microETXexpress) (95 x 95 mm). The ultra (nanoETXexpress) (84 x 55 mm) is expected to be integrated into the PICMG standard shortly. All the form factors are fully compatible with the COM Express standard. Mounting holes line up on each of the modules, and the cooling solution concept is the same, ensuring that basic and compact modules are interchangeable on carrier boards.

Fig. 1.: The evolution of size differences in basic, compact, and ultra form factor COM Express compatible modules.

Why they work

The steady flow of technology advances position COM platforms for scalable small form factor designs and high-value customization investments. Customization is done on the module’s carrier board rather than on the module itself. Once resolved in a design, customization can last for multiple generations with various CPU cores.

Designers work with a standard module which includes processor, bus, memory and I/O components. The COM can easily be replaced for one delivering any new requirements that may arise. COM Express modules are connected to the carrier board via one or two 220 pin connectors. Currently, the contact layout is specified in five different pinout types (type 1 to type 5) with interfaces for PCI, PCIe, PEG, Serial ATA (SATA), LVDS, USB, Gigabit Ethernet, AC97, and GPIOs.Cores can be upgraded with newer COM Express modules or the design can be upgraded within the COM specification. For example, the application could move from ETX technology into more current I/Os and interfaces found in COM Express.

The beauty of this solution is that it is not a core CPU module change, but an actual swap of the COMs technology implemented. These designs would require a new carrier board. However, because of the similarities to the ETX layout, designers would be able to use compatible software already developed.

Core benefits

For instance, an ETX-based design might have initially been developed using a Pentium core. From there, it could have made a performance jump to the Pentium M. And today that design can move into the Atom CPU – all within the ETX product family.

Also, COM Express standardized heatspreader dimensions ensure easy control of heat dissipation and are an important consideration in achieving true interchangeability. If new application demands warrant a deeper upgrade, ETX designs can be ported into COM Express. A likely design for this scenario is using the ETX-PM, which achieves high-end performance with low power. Designers can readily move to COM Express via the microETXexpress-DC, an economical Atom-based solution.

Moving with market developments

With advanced processing technologies, small form factors have seen game-changing improvements in the amount of performance they can deliver and the amount of power they use. For instance, the 45-nm Atom processor architecture achieves clock speeds between 1.1 and 1.6 GHz in a sub-5-W thermal power envelope and has a front side bus of up to 533 MHz for fast data transfer. This in turn enables the development of energy-saving, high-end graphics devices based on System Controller Hub US15W without leaving the safe and proven development path of COMs.

And, Core i7-based COMs solutions employ an efficient two-chip solution that provides better signal integrity and minimizes board space enabling higher performance for smaller, power-constrained portable designs. Performance-per-watt is as good as it gets, with enhanced I/O capabilities.

NanoETXexpress is the smallest-form-factor COM Express specification. For small handheld medical devices or wearable computers being used in battlefield environments, the 55 x 84-mm nanoETXexpress form factor is very useful. It is a 39% size reduction from the original COM Express module ETXexpress form factor and 51% from microETXexpress. It is compatible with the COM Express Type 1 connector, and nanoETXexpress allows access to a range of interfaces such as Gigabit Ethernet, 1x SATA port, 8x USB 2.0 and a PCI-Express x1. Product variations offer two PCIe interfaces and also support an external PCIe-to-PCI bridge.

COMs for rugged portable design

One of the most important trends for medical designs is size reduction and COMs support this particular path very well. A high-performance module such as the ETXexpress-PC can perform compute-intensive imaging that previously required a much larger single board computer, and an even smaller footprint can be achieved using microETXexpress-PC. Designers have a range of scalable performance options, and have options for sister devices that are resistant to shock and vibration and operate at extreme temperatures.

Fig. 2. COMs such as microETXexpress COMs can offer industrial temperature ranges of -40 to 85°C, as well as high tolerance for shock and vibration.

The military is another key application area for COMs, with ruggedized COM Express modules offering an excellent match for designs driving network mobilization efforts. Unmanned vehicles, field devices such as software-defined radios, and embedded devices enabling secure communications systems are benefiting from these reliable, compact components. COMs balance performance size, weight and power issues critical to mobile networks and man-wearable systems. ■