Forging new ground using existing COMs concepts

GUEST OPINION: Although highly popular embedded computing components that have been around for several decades, computers-on-modules (COMs) lacked the continuity needed to make these boards appeal to the various industries for which they were designed.

By Stephen Cunha, MEN Micro Inc. -- EDN, 1/23/2009

Although highly popular embedded computing components that have been around for several decades, computers-on-modules (COMs) lacked the continuity needed to make these boards appeal to the various industries for which they were designed. With no set standard for design, pin out, component compatibility or technological upgrades, COMs never provided its intended commonality among board manufacturers.

COMs, a complete computer on a mezzanine card incorporates a CPU board with customization only on the carrier board as a standard feature. It was initially developed to provide ‘standard’ time and cost-savings benefits. Yet, with no committee really steering the ship, each manufacturer seemed to be making customized COMs solutions that really did not fit in with other available designs. In fact, some reports claim there are over 50 ‘standard’ COMs designed among embedded computing manufacturers. The benefits were never fully realized, but the concept itself was a good one.

Also, there were a few inherent flaws in the initial COMs concept. Heat generated from the boards was still a major problem. In addition, there were no provisions for more rugged or mobile environments that greatly benefit from embedded computing and face the same time-to-market and budget constraints of less harsh applications. These were the multifaceted challenges facing MEN Micro when we set out to make COMs something a little more stable and cost-effective for a wider number of application areas.

We were intent on developing an industry-wide standard that would mitigate these initial design flaws and move the embedded computing industry towards a more unified way of providing cost-effective computer systems that provided long-term benefits.

The first aspect that we tackled was the cooling component, as this was the more complex task and would impact the ruggedization and design of the board. We decided to focus on the existing structure of COMs boards, versus adding components or modifying the design too drastically. We still wanted pre-existing COMs concepts to be able to employ this new standard concept, dubbed ESMexpress and currently in review with VITA to be an ANSI standard (VITA 59 RSE: Rugged System-on-module Express). In fact, VITA 59: RSE complies with the COM Express basic form factor via an adaptor board, and includes the five screw holes defined from COM Express.

The VITA 59: RSE features a populated PCB, with a small size of only 85 mm x 115 mm and mounts on a frame with a final size of 95 mm x 125 mm, all completely enclosed in an aluminum housing. The edges of the PCB clip onto the frame without screws, and the high pressure from the safe joints between the housing and the PCB enables the heat to transfer from the PCB to the frame and then to the housing cover. The frame also leads the carrier board heat to the housing cover. This unique, fanless cooling concept helps dissipate up to 35 Watts, which is the upper limit of dissipation for a fully developed Intel Core 2 Duo architecture.

Ruggedization was the next aspect we needed to address, since we were aiming to bring the time and cost-savings of the ESMexpress concept to a wider number of industries. The aluminum housing is hermetically sealed on all six sides to provide 100% EMC protection. In addition to a connector specified for military and railway operations and supporting differential signals of up to 8 GHz (16 Gbps), the compact module is secured to the carrier board using eight screws. This provides extremely better shock and vibration resistance than the typical COMs design.

Longevity came up third on our list of ways to make this concept stand the test of time and the environments in which these boards would need to perform. By looking extensively into the technology roadmaps currently offered by CPU manufacturers, we decided to incorporate serial buses, not switched fabrics, into the standard. This includes technologies from PCI Express and Ethernet as well as SATA and USB. Switched fabrics, which have a home in modular computing architecture such as VME, are just not suitable for COMs environments, especially in light of where current technologies are heading.

We also standardized as much of the architecture as possible. Two 120-pin connectors incorporate a fixed pin assignment to facilitate inter-compatibility among components. An FPGA on the carrier board enables the implementation of legacy interfaces or added modularity and I/O functionality.

By evaluating available data, learning from some mistakes in the industry and applying a good degree of engineering acumen, we were able to develop a new concept that gives designers of embedded computing systems more flexibility, increased reliability and better performance in a package this will both extend their budget and help them build systems faster.

For updates on VITA 59: RSE, please contact MEN Micro’s project management team at pm@men.de. For publicly available information visit http://men-intra/products/default.asp?fa=esm&about=esmexpress&h=About%20ESMexpress. The next review is set for VITA’s fall meeting.