MicroTCA Comes on Strong
MicroTCA Challenges VPX-Based Systems for Military Applications
In the low-cost, high-performance, open system trade space, MicroTCA is often paired with VPX/OpenVPX. MicroTCA’s ATCA legacy, and its recent expansion into the hardened system domain, makes it a viable option for both benign and rugged military applications.
MARK LEIBOWITZ, ROBERT SARACINO AND JON LEACH, BAE SYSTEMS, ELECTRONIC SYSTEMS AND SAEED KARAMOOZ, VADATECH
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- Figure 1 - The MicroTCA family of standards of...
- Figure 2 - Hardened MicroTCA module clamshell ...
- Figure 3 - The efficacy of the PWB edge pad de...
- Sidebar -
- Table 1 - Recent development of hardened, air...
- Table 2 - While sharing many features, a numb...
- Table 3 - Testing for MicroTCA.3 was more com...
PICMG’s Advanced Telecommunications Computing Architecture (ATCA) has grown to become a billion-dollar market. As a stable, mature standard grounded in a modular, open systems approach, ATCA has expanded beyond its telecommunications origins and has established a footprint in other industries, including SATCOM, process control and high-energy fusion physics. See the sidebar titled, “Why a Modular Open Systems Approach (MOSA)?” p.55
ATCA’s compliance to NEBS requirements, high availability (99.999%) and substantial system throughput (2 Tbit /s) are features that also make this standard highly desirable for demanding, mission-critical military computing applications. The U.S. Navy, for example, uses ATCA-based mission computers and operator consoles on the P-8A Poseidon platform. The Navy has also embraced ATCA for programs such as Consolidated Afloat Networks and Enterprise Services (CANES).
ATCA is supported by an extremely healthy vendor ecosystem offering highly interoperable products. The PICMG 3.0 standard, which covers all aspects of the electrical, mechanical, cooling and power subsystem properties, governs this interoperability.
MicroTCA Expands Beyond its Telecom Origins
ATCA has also spawned a series of standards for small form factor rugged computing components called MicroTCA. In its AMC.0 standard, PICMG defines a mezzanine building block approach for the addition of crucial functionality in the form of Advanced Mezzanine Cards (AMCs) to an ATCA carrier card. The MicroTCA base specification, or MicroTCA.0, is complementary to ATCA and defines a system where these AMCs can be used outside of an ATCA carrier, that is, within its own chassis and backplane. MicroTCA thereby enables the creation of systems with many of the ATCA advantages in a smaller, more energy-efficient size.
MicroTCA’s ability to draw from the ATCA ecosystem means that a large number of AMC modules are already available for use in rugged MicroTCA applications without modification, except for screening, staking and conformal coating as required.
The MicroTCA architecture is well suited for high-performance computing and networking functions. It defines switched fabrics, including requirements for 1GigE, 10GigE, PCIe (Gen 2), SRIO and SATA/SAS fabrics. It also incorporates redundancy of both power and MicroTCA carrier hub (MCH) modules. Moreover, it offers inherent hardware platform management (HPM) functions that use the same software tree as ATCA.
To expand its reach into more rugged, demanding environments, MicroTCA working groups have defined a number of specialized MicroTCA implementations with a common goal–reuse of the same AMC printed circuit boards and as much of the MicroTCA base specification infrastructure as possible. Figure 1 shows the five specifications that govern MicroTCA systems. MicroTCA.3 and MicroTCA.2 specifically target the military market.
The MicroTCA family of standards offers varying levels of ruggedization to meet commercial, industrial, and military environments. The MicroTCA.3 specification was released in February 2011; MicroTCA.2 release is expected early in 2012.
Hardened MicroTCA Targets Military
MicroTCA addresses the severe shock and vibration environments typical of many military air, land and sea applications with the MicroTCA.3 and MicroTCA.2 specifications, which define a hardened design approach for conduction and forced-air cooled systems, respectively. Each benefits from key input from military vendors, such as BAE Systems and Boeing, and include well-defined test procedures for a consistent reading of vendor compliance.
The MicroTCA.3 Hardened Conduction Cooled specification provides the requirements necessary for a system to meet the rugged requirements of outside plant telecom, machine and transport industry, and military airborne, shipboard and ground mobile equipment environments. Released in early 2011, the specification defines five ruggedization levels, or product classes–two telecommunications grade and three military grade–intended for applications where air flow over the modules is not available. Closely related to MicroTCA.3 is the MicroTCA.2 Hybrid Air/Conduction Cooled specification, which defines four military grade ruggedization levels of its own. With an expected release in early 2012, it defines a forced-air cooled system that targets rugged industrial and military applications. Table 1 compares Hardened MicroTCA’s VITA 47-based key environmental requirements to those of the MicroTCA base specification.
Recent development of hardened, air and conduction-cooled standards aligned to VITA 47-based environmental requirements makes MicroTCA a worthy candidate for a wider range of rugged military applications.
As depicted in Figure 2, hardened MicroTCA encloses AMC PCBs, MCHs modules and power modules in electrically conductive heat frames (clamshells), which are fitted with card retainers to harden the circuit boards, protect electrical connections from shock and vibration, and provide a thermal conduction path to the chassis. For MicroTCA.2 systems, this conduction path is a beneficial by-product of the hardened design, and serves to augment the dominant forced-air cooling effect–thus its “hybrid” cooling designation.
Hardened MicroTCA module clamshell design—vented in the case of MicroTCA.2—protects active PCB circuits from ESD damage, thus allowing for the logistical and cost benefits of a two-level maintenance approach.
In November 2011 the MicroTCA.2 working group will be performing thermal testing of both low- and high-power representative test modules. Testing will measure airflow resistance and resulting temperature gradients of test modules to characterize the cooling capability of the hybrid air/conduction cooling approach.
MicroTCA and OpenVPX–Different Legacies, Common Goals
While MicroTCA and VPX have much in common, their different origins may influence prevailing opinions as to which best applies to the demands of high-performance military embedded computing systems. For some, the fact that VPX technology succeeded VME with rugged military applications specifically in mind affords it a certain incumbency–a status only strengthened by the interoperability advances of OpenVPX. However, hardened MicroTCA is a strong competitor. As shown in Table 2, MicroTCA meets the same environmental requirements as VPX, is less expensive, and is more “open” than OpenVPX. Additionally, MicroTCA has performance advantages in the areas of both backplane fabric technology and the inherent hardware platform management (HPM) available to MicroTCA systems.
While sharing many features, a number of key performance and implementation differences tip toward MicroTCA’s advantage—in particular, a mature HPM capability leveraged from ATCA that contributes to very significant edge in cost.
AdvancedTCA has long leveraged its widespread acceptance in commercial network-centric applications to gain solid ground in many benign-environment communications-centric military applications. Since MicroTCA derives from ATCA, these applications are easily scaled for small form factor applications. MicroTCA’s commercial roots, unlike those of military-centric VPX, broaden the range of solutions available to the developer. Moreover, MicroTCA’s recent VITA 47-based rugged implementations—and hardened variants in particular—are attractive for these applications because they combine net-centric performance and low cost with the ability to overcome severe temperature, shock and vibration challenges.
It is worth noting that as shown in Figure 3, both MicroTCA and VPX use PWB edge pads with very similar characteristics for high-speed interconnect. To ensure a robust backplane-to-AMC connector system in rugged environments, the PICMG MicroTCA.3 working group sponsored chassis-level testing prior to releasing the MicroTCA.3 specification. Testing consisted of eight full-life test groups plus a separate ESD test. Similarly, prior to releasing the VITA 46 (VPX) specification, the VPX working group sponsored holding-fixture testing to validate its own backplane-to-VPX module connector system. Testing consisted of seven test groups. In each case, Contech Research of Attleboro, MA, an independent testing and research company, performed the testing. Table 3 highlights the results—and differences in duration and severity—of the test regimens.
The efficacy of the PWB edge pad design concept common to MicroTCA and VPX for rugged applications was one driver of extensive connector system testing.
Testing for MicroTCA.3 was more comprehensive than for VPX, with testing performed over a longer life duration and against more failure mechanisms using VITA 47-defined environments—including 500 hours thermal cycling for MicroTCA.3 versus 240 hours for VPX.
In terms of architecture software, MicroTCA supports open, free operating systems and drivers natively. While this support extends primarily to Linux and Windows, support for other operating systems is available. Free or minimal-cost operating systems and all associated PCI-E hardware drivers allow for low-cost solutions. In contrast, VPX and OpenVPX support mainly operating systems such as VXworks, which carry a high cost for the software and drivers.
Further, MicroTCA uses multi-vendor, open-source connectors, whereas VPX and OpenVPX use a single vendor’s patent-pending connector system.
An energized, expanded vendor ecosystem willing to invest in competing technologies is good news for military and other users of high-performing, network-centric embedded computing products, as it stimulates competition to develop the low-cost, high-performance solutions needed for demanding military environments. Robust vendor support has been a key driver of the evolution of ATCA into the rugged air- and conduction-cooled variants of MicroTCA.
At present, MicroTCA costs less than VPX products. When considering the cost of developing a HPM capability, VPX cost may exceed that of comparable MicroTCA implementations by as much as 50 to 100%. MicroTCA’s lower cost and open source advantages, coupled with its ability to meet the same environmental requirements as VPX and its performance edge in backplane fabric technology and HPM, make it an appealing choice in the small form factor military embedded systems domain.
BAE Systems, Electronic Systems