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MicroTCA for Mil/Aero Emerges

Mon, 03/09/2009 - 6:04am
By Clayton Tucker, Emerson Network Power; and Bob Sullivan, Hybricon


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Figure 1. The MicroTCA specification provides system design flexibility, allowing the footprint to take on a wide variety of forms.
In military and aerospace design, the push is underway to replace proprietary architectures with COTS systems that can successfully integrate high density, multicore processors and multi-compute nodes. The MicroTCA architecture, originally developed for telecom and networking applications, is now evolving ruggedized construction specifications that can support mil/aero designs.

Manufacturers and vendors in the mil/aero industries are recognizing the value of standards-based, commercial off the shelf (COTS) technologies and are looking at new technology architectures as the basis for their network centric program initiatives and new designs. Previous generations of COTS equipment, however, were developed for enterprise applications and lacked the tolerance of shock, vibration, extended temperatures and other environmental hazards that are required for military and aerospace (mil/aero) systems. The MicroTCA architecture is an exception, now evolving to embrace ruggedization and become the basis of next-generation mil/aero designs.

Following a COTS design approach based on open standards offers developers many benefits. One is a reduction in the design effort, saving both time and expense. Most of the hardware needed for a system design is already available and guaranteed to interoperate. Similarly, much of the foundation system software has already been developed and tested against the hardware. This availability frees the development team to concentrate its design efforts on meeting the unique requirements of their application, a much smaller task.

The standards-based design approach also offers benefits of lowered cost, wider availability, and increased innovation compared to proprietary designs. Vendors of standards-based system elements have the opportunity to participate in a broad market without having to first create one. This broad market allows for increased competition, which increases product availability. The broad market also leads to innovation as vendors work to differentiate their products by enhancing functionality within the standards envelope rather than expending effort re-inventing the foundation.

Another benefit of the broad market that standards-based design fosters is a reduction in product cost. Vendors are able to achieve higher volumes, realizing economies of scale in their manufacturing. Competition ensures that these economies of scale pass through to the customer. This cost benefit adds to the savings developers realize from the reduced design effort.


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Figure 2. The system management built into the MicroTCA specification supports hot-swap and high-availability design, as well as providing system monitoring and control down to the module level.
Achieving these benefits was one of the motivations for the PCI Industrial Computer Manufacturer’s Group (PICMG) in developing open system, hardware, and software specifications tackling the needs of telecommunications and networking equipment. One of their recent results, the Advanced Telecommunications Computing Architecture (ATCA), uses a modular design approach that plugs a variety of blades into a high-speed, protocol-agnostic, switched-serial backplane. The blades are also modular, configurable with I/O and computing functions on Advanced Mezzanine Card (AMC) modules that plug onto the blade. The ATCA specifications define the entire base system; including cards, cage, power supply, cooling and system software for built-in test, fault monitoring, and system management.
The Next Big Thing: MicroTCA Basics
To address a need for more compact designs, PICMG developed MicroTCA as an offshoot of ATCA. MicroTCA uses the same architecture, AMC modules, and system management software as ATCA. This allows many system hardware and software elements created for ATCA to also serve in MicroTCA designs. The primary difference is that MicroTCA calls for AMC modules, which are large enough to carry significant functionality but small enough to fit into a shoebox-sized housing, to plug directly into a backplane rather than onto the 8U carrier cards. The switch is built into an AMC sized MicroTCA Carrier Hub (MCH) instead of on the individual 8U ATCA cards. This is the intelligence and functionality behind MicroTCA platforms.

The AMC modules that are common to both ATCA and MicroTCA were defined with telecom’s need for high-availability system operation in mind. Working in conjunction with the system management software, the modules support remote power control for hot-swap operations. They also incorporate built-in test capability and support advanced features such as electronic keying and automatic fail-over in case of fault. Together with the modularity inherent in the MicroTCA architecture, the AMC module features and system management greatly simplify system maintenance, repair and upgrade.

MicroTCA arose to address the needs of compact system design, so its specifications allow considerable flexibility in development choices. A full system can be implemented with only 2 AMC modules or incorporate as many as 12 in a cage. The cage itself is also flexible, as shown in Figure 1. Systems can be implemented as racks, cubes, or many other configurations and still conform to specifications, thus enjoying access to the many available COTS components.

Figure 3. This conduction-cooled MicroTCA system from Hybricon is a harbinger of ruggedized specifications currently under development within PICMG.
The COTS components that are available for MicroTCA span the entire system design. Cage mechanics, power and cooling subsystems, and backplane are all covered in the specifications and available from multiple vendors. A wide range of AMC modules are likewise available with such functionality as high-performance CPUs, high-speed serial interfaces, mass storage systems and other telecom system needs. But the market for MicroTCA system elements is also growing beyond telecom, making even more diverse functionality available.

In addition to defining system hardware, the ATCA and MicroTCA specifications define a complete base system behavior including fully-defined system management functionality. As a result, system software for MicroTCA is also available as COTS products.

Emerson Network Power’s SpiderwareM3 middleware, for example, helps simplify the managing, monitoring and maintaining of MicroTCA systems by giving an operator access to and control of system behaviors, such as module discovery and identification, environmental monitoring and alarm setting, fan speed and operation and software loading. Such software is assured to be interoperable with specification-compliant system hardware.
System Management Differentiates MicroTCA
The system management and high-availability features built into the MicroTCA specifications differentiate it from other open standards and make it particularly applicable to the needs of mil/aero system designs. MicroTCA systems have built-in test features, such as the monitoring and control of internal temperature, power supply levels and other system attributes using sensors the specifications require to be in place.

System management extends to the monitoring and control of individual modules within the system (See Figure 2). The specification calls for independent, remote-controllable power feeds to a module’s core and to its interface, giving system management the tools to shut down a module and prevent it from affecting backplane traffic if a module has failed or is improperly inserted.

Figure 4. Ruggedized AMC modules for conduction cooling will still retain much in common with the original designs, although mechanical dimensions for card cages may change.
This capability also allows system management to respond to the addition or removal of a module from a live system, supporting hot-swap replacement and fail-over operations. Staggered power leads and hardwired identification signals on the module’s edge connector further support hot-swap and electronic keying. Hot-swap support in MicroTCA also includes system elements beyond the AMC modules. Both the cooling fan and the power supply are also hot-swappable, simplifying field replacement and providing an opportunity to design in redundancy to increase fault tolerance.

This opportunity is the foundation for high-availability (HA) system design, and the open nature of the MicroTCA standard has allowed COTS HA middleware to arise. Using the features built into the MicroTCA standard, the Service Availability Forum – an industry-wide consortium – has developed HA middleware that is freely available for developers to adapt and apply to their system designs. Commercial HA middleware, which includes full support engineering, is also available.

Along with high-availability and system management, another differentiating feature of the MicroTCA architecture is its protocol-agnostic backplane. The backplane supports as many as 21 high-speed serial links to each module in the system and incorporates switching to create star, mesh and other connection configurations.

Because these links aren’t unique to a specific serial communications protocol, developers have substantial flexibility in the type of networking their designs will support. One possibility, for example, is to use the IP protocol for all inter-module communications. This allows the system to connect directly to an IP network from the backplane without the need for any additional interfaces or protocol converters, increasing performance and decreasing cost.

The benefits of open-specification design and the many attributes that support mission-critical operation make MicroTCA a promising architecture for mil/aero system designs. The 1 weak area, until now, has been in ruggedization. The original PICMG specification released in 2006 - MicroTCA.0 - calls for adherence to NEBS-grade environmental conditions. These represent office-environment and outbuilding conditions, a -5°C to 55°C ambient temperature range, and resistance to normal shipping and handling, installation activity, earthquakes and similar situations.
Ruggedized Specifications Emerge
Within the PICMG organization, however, efforts have been underway to create specifications extending these limits to address harsher environment installations, including outdoor settings, vehicle mounting (including trucks, trains and commercial aircraft) and industrial settings. The first of these extended specifications - MicroTCA.1 - is scheduled for release in 2008 and defines a ruggedized, air-cooled MicroTCA architecture. The goal is to keep intact as much of a MicroTCA.0-compliant design as possible, to preserve cost benefits, using component selection during board build and mechanical hardware that augments existing designs to boost ruggedization, rather than requiring fundamental design changes.

The MicroTCA.1 specification calls for an air-cooled system and defines several possible ambient operating temperature ranges, the broadest of which is -40°C to 70°C. It also calls for new retention devices to be added to the AMC card and cage specification. Extensive testing has proven that incorporating these retention devices allows the current card-edge connector system to meet a 5G to 25G shock and 10G sinusoidal vibration immunity requirement. Work is ongoing to test this configuration with more severe random vibration profiles to serve military mobile applications as well.

An additional extension defining a conduction-cooled system – MicroTCA.2 – is also under active development, although not as far along as the air-cooled specification. This conduction-cooled MicroTCA specification aims at meeting many of the ANSI/VITA 47 environmental levels, including an operating temperature range of -40°C to 85°C.

The specification also adds random vibration to the shock/vibration specification. Although the specification has not been fully defined and approved, conduction-cooled MicroTCA units are already available from companies such as Hybricon (See Figure 3) that point the way and prove the concept.

As with the air-cooled specification effort, the PICMG committee defining MicroTCA.2 seeks to retain as much of the original design as possible to maximize the cost savings. Several significant changes will be required, however. One is the use of wedge locks and conduction plates on the AMC modules to carry component heat to the frame (See Figure 4).

At a minimum, these additions will require changes to the card cage spacing and dimensions. The edge connector is also a potential change site, although preliminary testing indicates that some versions of the connectors will be acceptable for many applications. The committee plans extensive testing to fully characterize the conditions for which connector options have sufficient reliability.
Conclusion
These efforts within PICMG are taking MicroTCA over the final hurdle for its use as a design basis for all but the most demanding mil/aero applications. The architecture has already been proven in telecom and other system designs and fostered a growing ecosystem of hardware and software vendors. The flexibility inherent in the architecture encourages further growth in the number and types of COTS offerings that will become available, while also allowing mil/aero developers to create the differentiating features that their applications require.

Soon, air-cooled, and, later, conduction-cooled, specifications will be in place, allowing MicroTCA vendors to begin offering products covering a range of environmental options. MicroTCA will thus give mil/aero designers the ability to select a cost-effective combination of COTS system elements that matches their functional and environmental requirements at minimum cost.

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