Although based on a concept that has been around for several decades, Computers-On-Modules (COMs) have lacked the robustness and standardization since their inception that would enable wide proliferation of these cost-effective computing modules into embedded systems.
With no set standard for design, pin-out, component compatibility or technological upgrades, and several manufacturers developing their own “secret sauce” to implement them, COMs never provided the intended commonality and lowered development costs among board manufacturers. Nor did they initially possess the structure to withstand rugged environments, which are becoming more commonplace in a wide variety of embedded computing applications.
First steps to mass deployment
The COM concept incorporates a complete computer on a mezzanine card with a CPU board that requires customization only on the carrier board as a standard feature. It was initially developed to provide “standard” time- and cost-saving benefits.
Yet, with no committee really steering the ship when COMs were first developed, each manufacturer seemed to be making customized solutions that really did not fit in with other available designs. In fact, some reports claim there are more than 50 “standard” COM designs among embedded computing manufacturers. The compatibility benefits were never fully realized, but the concept itself was a good one.
Additionally, the initial COM concept contended with some common industry design problems, most notably heat generation and lack of ruggedization. As embedded technology made its way into an increasing number of mobile, rugged, and harsh environments, COMs needed an update in order to be used effectively in the growing embedded arena.
Initiated in 2008, the ESMexpress standard, known as VITA 59: Rugged System-on-module Express (RSE), began the process of bringing all COM design elements under one umbrella to enable true realization of the concept’s compatibility features. ESMexpress utilizes the same 125 mm x 95 mm board size as the previous COM Express form factor.
Common industry design considerations are also a part of the new standard, currently slated for completion in 2013. The CPU roadmaps of different manufacturers РIntel and Freescale, for example Рhave been brought into account. And, with the reinstitution of VITA 59: RSE for completion this year, compatibility with COM Express has been added for even more flexibility in COM-based application development. For extremely compact situations, a subset concept has been developed as well: ESMini, measuring 95 mm x 55 mm. While not officially part of VITA 59: RSE, ESMini still provides the same rugged performance as the upcoming standard.
Considering the design environment
Both COM types are resistant against temperature, shock, vibration, and EMC influences and have to function reliably and according to the relevant standards in life-critical applications or applications that entail high costs in case of failure. These include applications in ground transport or airborne equipment, mobile computers of any kind in transportation, avionics or medical engineering, as well as outdoor computers and critical industrial control equipment.
On ESMexpress, the signals are led to two 120-pin connectors and exclusively defined for modern serial buses like PCI Express, Ethernet, SATA, USB, etc. The pin assignment is fixed without options in order to guarantee 100 percent interchangeability between the modules. This means that legacy I/O that might be required as well as additional modularity can be implemented using FPGAs on the carrier board.
For ESMini, both the form factor and the pin assignment is variable. Thanks to this flexibility, components with different sizes can be used, and additional individual I/O in the onboard FPGA can be realized beside the serial I/O.
The most important feature of ESMexpress and ESMini is the fanless cooling concept designed for a power dissipation of up to 35 W. The electronics are completely sealed in an aluminum enclosure. If the power dissipation of the COM requires additional cooling, the housing is either connected to an external heat transfer device (conduction) or combined with a heat sink for heat dissipation (convection). The dissipated heat can also be led from the cover via the frame to a carrier board that supports conduction cooling. At the same time, the closed aluminum enclosure offers optimum EMC protection. As the module is mounted on the carrier board, all six sides are hermetically sealed. The connector of both COMs, qualified for MIL and railway applications, supports differential signals with up to 8 GHz and is specified for -55 C to +125 C.
Standardization on the horizon
The cost-effectiveness and design simplicity of COMs is finally ready to be fully realized with the upcoming VITA standardization, as well as through the support of several industry manufacturers.
It is these types of innovations that will keep embedded computing at the forefront of the technology landscape, as more opportunities are created for companies to employ ruggedized, efficient, standardized computing concepts.