Open standards have been around for embedded computing for more than 30 years. The first standards, including S-100 and the STD bus, came and went. The IBM PC bus was arguably the most successful open microprocessor standard. VMEbus, which arrived in the early 1980s, is still alive and kicking although mostly for legacy applications. These have all largely been replaced with switched serial buses, as integrated circuit pins became expensive and transistors became virtually free. The appeal of open architectures is easy to understand: Many suppliers reduced engineering expenses and time to market, as well as price competition.

Many of the popular open standards used to be fairly segmented by market. The military used VME; industrial vendors used PC/104, PC, and PCI buses; and suppliers of communications equipment used CompactPCI and now use AdvancedTCA and MicroTCA. The market segmentation is beginning to blur as more and more applications require high reliability, major computing power, and fast, reliable packet-based communications. This trend favors architectures that are specifically designed with these attributes. AdvancedTCA, originally intended for central office telecom use, is now being used in a wide range of application spaces, including military, SATCOM, process control, and high-energy and fusion physics. AdvancedTCA is a stable and widely deployed platform, showing up in places such as the U.S. Navyís P-8A Poseidon subhunter aircraft. Lockheed Martin has deployed AdvancedTCA systems for the Integrated Shipboard Network System (ISNS). AdvancedTCA is also being considered for the much larger Consolidated Afloat Networks and Enterprise Services (CANES) and has already passed some important environmental and shock tests.

Perhaps more surprising is the militaryís interest in MicroTCA, AdvancedTCAís little brother. It shares many attributes of AdvancedTCA, from which it was derived, but in a smaller footprint. It offers scalability, integrated management, high availability, and redundancy if needed and is supported by many dozens of suppliers. Hybriconís Bob Sullivan and Emerson Network Powerís James Doyle wrote in the May 2009 issue of Military Embedded Systems magazine about some of the work PICMG is doing to ruggedize MicroTCA to meet published military requirements, and I want to expand a bit on their articleís theme.

MicroTCA, like AdvancedTCA, was originally developed for relatively benign telecom applications. More so than AdvancedTCA, it was felt that the original specification, MicroTCA.0, needed to be ìbeefed upî to make it suitable for tough environments like armored vehicles and aircraft, both manned and unmanned. Thus, there are three follow-on specifications being developed, one of which was already ratified and released, that build on the original platform to provide ever-higher levels of ruggedization. Figure 1 (MicroTCA Guide) depicts the family tree.

Figure 1: This MicroTCA Guide shows where MicroTCA came from – and where itís going. (click graphic to zoom by 1.7x)

MicroTCA gets rugged

MTCA.1, the rugged air-cooled version, was ratified in March 2009. It is primarily intended for non-central office telecom environments, including outdoor and pole-mounted equipment. It uses standard AdvancedMC cards and card racks. Improved card retention mechanisms are described as well as techniques for shock mounting and ìcocooningî the card racks. Two temperature ranges are specified, but neither is completely suitable for many tough military applications.

As mentioned, two follow-on versions of the standards are also under development – MicroTCA.2 and MicroTCA.3 – and are being called ìhardenedî versions of MicroTCA. Both of these have significant input from, and contributions by, military vendors including BAE Systems and Boeing. These versions are being developed from the ground up for military use and include well-defined test procedures so that vendor compliance can be established in a consistent manner. There are a couple of features, including built-in self test and high-availability capability, that competing architectures such as 3U VPX do not provide.

One important goal of these two hardened platforms is the ability to perform two-level maintenance in the field. This has long been on the militaryís wish list, as field replacement at the card level without having to remove the entire piece of equipment and send it off to a repair depot has obvious logistical time and cost benefits. The major challenge for this is Electrostatic Discharge (ESD) protection, as any exposed component or trace must be able to withstand several kilovolts of static discharge. Extreme environments with blowing sand or blowing snow can produce large static buildups. The approaches to solving this and providing the cards with necessary protection involve clamshells around the AdvancedMC cards themselves. The hardened air-cooled version (Figure 2) uses vented sheet metal covers, and the hardened conduction-cooled version (Figure 3) uses conventional conduction-cooled plates and wedge locks for heat removal.

Figure 2: A hardened MicroTCA.2 air-cooled module

Figure 3: A MicroTCA.3 hardened conduction-cooled module

Hardened MicroTCA systems fit nicely in conventional full- and half-size ATR boxes, as Figure 4 demonstrates.

Figure 4: A conduction-cooled system in an ATR box, courtesy of BAE Systems. (click graphic to zoom)

When these specifications are completed, the market will be able to choose from a wide range of performance and price points. The VITA 47 environmental specs are being used to define the various levels of ruggedization, storage, and operating temperatures. Figure 5 shows the range of storage and operating temperatures that can be achieved with each version of MicroTCA.

Figure 5: The PICMG MicroTCA Specifications temperature graph

Testing in the forefront

One concern of both vendors and the user community has been the reliability of the high-density, high-speed connector system used in MicroTCA. As a result, connector testing has taken on high importance, and I am pleased to report that a series of rigorous tests (to date) have met all pertinent requirements. At PICMG, we are working on making the test reports a little more user friendly and expect to have them posted on the PICMG website shortly. And finally, I want to thank Mark Liebowitz from BAE Systems for most of the figures shown herein. They are from his presentation on ruggedized MicroTCA at the recent MicroTCA Summit.

 For more information, contact Joe at jpavlat@opensystemsmedia.com.