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Military applications represent some of the most challenging and broad-ranging design demands today. New technologies can be difficult to adopt and develop quickly, and as a result military markets frequently demand reliance on existing or legacy technology for speed and execution of a given design. On the other hand, new military programs, such as Future Combat Systems (FCS), Joint Tactical Radio System (JTRS) (Figure 1) and the Warfighter Information Network-Tactical (WIN-T) are so demanding and communication-centric, they require more performance than earlier architectures have been able to deliver within a small footprint. Wherever the application demands fall in terms of performance, designers must also consider issues of size, weight and power (SWaP), all critical to the overall performance of sensitive military applications.
When military budgets address not only cost, but also development time, enclosure space and performance factors, PC/104 or PC/104-compatible systems very effectively fit the bill. Stable platforms such as PC/104 and PC/104-compatible can be ideal for designs that do not require much, if any, hardware customization, and they have evolved to deliver increased performance within very small form factors.
For more complex applications, military designers may consider computer-on-modules (COMs) such as ETX or COM Express including the Basic and Extended form factors in addition to compatible compact modules such as microETXexpress or nanoETXexpress. When communication and bandwidth requirements go beyond the limits of these established technologies, 3U CompactPCI and MicroTCA can step in with increased computing power, very high communication bandwidth and high availability in a small form factor. Table 1 compares the major standard small form factors available and their suitability for various defense applications.
PC/104 for Non-Custom Designs
As an off-the-shelf product, PC/104 and PC/104-compatible modules tend to be the norm for military applications in which very low cost, small footprint and moderate performance are among the main criteria. With little or no customization, these solutions prove more than sufficient for a wide range of implementations.
Comprised of a CPU board and optional peripheral boards stacked together, PC/104 eliminates the need for a motherboard, backplane or card cage. Fitted with stack-through connectors, these pin- and socket-bus connectors provide a reliable signal path even in harsh environments. With four corner-mounting holes for board support to resist shock and vibration, each module measures 3.575 inches x 3.775 inches (90 mm x 96 mm). When stacked, the card spacing is 0.6 inches.
The bus specifications for PC/104 are identical to ISA’s with the exception that PC/104 reduces the drive requirement for most signals to 4 mA of sink current reducing overall power requirements and allowing ASIC devices to directly drive most bus signals without the need for separate driver components. PC/104’s stability as a form factor and wide availability from nearly 75 vendors, make it an attractive option where “easy does it” and optimum performance is simply not necessary.
COMs Win for Modularity
Computer-on-modules put an entire computer host-complex power on a small form factor module. This is then mounted on larger carrier boards containing application-specific I/O and power circuitry. These off-the-shelf compact modules readily contain all generic PC functions, such as graphics, Ethernet, sound, COM and USB ports, and other system buses. The custom designed carrier board complements the COM with any additional functionality required for a particular application.
COMs have been standardized through the Embedded Technology eXtended (more commonly referred to as ETX) standard, providing full PC functionality, minimum engineering and adoption cost, reliable connectors, slim design, and simple upgradability and scalability.
ETX modules are highly integrated and compact (95 mm x 114 mm, 12 mm thick) COMs. The standardized form factor and connector layout that carry a specific set of signals–found in all ETX modules–means designers can create a single-system baseboard, which will accept current and future ETX modules. Being able to build a system on a single baseboard using the computer as one plug-in component simplifies packaging, eliminating cabling and significantly reduces system-level cost–all key issues to mil/aero design.
ETX has further evolved, making advancements in its scalability and performance. The newer ETX 3.0 specification offers the same benefits of the original ETX standard, but also adds in 2x Serial ATA with no change in ETX pins, making new modules 100 percent pin-to-pin compatible with previous versions to ensure long-term support. Evolution continues with COM Express and its specifications that satisfy the higher performance market segments of the military and illustrate the trend toward size reduction and mobility. Figure 2 compares the sizes of the various COM standard form factors.
ETXexpress–a COM Express solution from Kontron–modules are 100 percent compliant with the COM Express spec and allow the application of high-speed COMs for PCI Express Bus and PCI Express chipsets. The new 220-pin high-speed SMT connectors for ETXexpress offer enormous performance capabilities. ETXexpress supports hardware solutions that are based on current bus systems such as 32 PCI and LPC (the ISA bus replacement) as well as up to 32 PCI-Express lanes (configuration dependant) including PCI Express Graphics. Gigabit Ethernet, USB 2.0, Serial ATA and Parallel ATA interfaces are supported as well.
Initially, COM Express was designed to accommodate the next generations of PCI Express (5 GHz) and Serial ATA (300 Mbits/s) interfaces, effectively doubling existing data rates to 160 Gbits/s and 1.2 Gbytes/s. For new and more portable military applications, designers now have additional options available in the COMs standard, including the microETXexpress (with a more compact footprint at 95 mm x 95 mm) and nanoETXexpress (with a minimized footprint that is just 39 percent of the original COM Express standard “Basic” form factor module) COM Express compatible modules.
COMs are appropriate for designs that include a lot of application-specific customization and can afford a two-board solution–module plus custom carrier board. Well suited to a high run of product and the need for some scalability from generation to generation, COMs are ideal for devices or applications that not only require scalability from generation to generation, but also within a single generation. Customizations designed into COMs’ accompanying carrier board can last for generations with various CPU cores, for example, swapping out one for the next.
3U cPCI Accepted by Military
3U implementations of established architectures such as VME and CompactPCI can also address legacy issues inherent to military designs, and now offer new features that meet more requirements of harsh computing environments. For example, VME is more than well established in military design, and mil/aero is VME’s largest market segment by revenue. As application requirements move toward requiring more bandwidth, 3U VME is less able to meet military’s size and performance demands. In addition to limited industry support, 3U VME is also limited in terms of bus width, bandwidth and rear I/O pins, and these limitations eliminate it as a design choice for many applications. A 64-bit bus is not possible with 3U VME, so many designers turn to 3U CompactPCI, which has much higher bandwidth, Gigabit Ethernet capabilities and more powerful rear I/O.
Also VME in general presents far greater software development challenges than CompactPCI. A more extensive range of software is PCI-compatible in nondefense applications, and that comfort zone has crossed over for mil/aero designs. Even newer software engineers are familiar with PCI-based programming. So, many years later, CompactPCI’s staying power in military design is not only strong, but growing based on its ability to deliver rear I/O in a smaller 3U form factor, powerful industry support and the latest processing technology available on CompactPCI boards.
3U CompactPCI is rugged and can be air-cooled or conduction-cooled and has Rear I/O, unlike PC/104 and MicroTCA. It’s also inherently stiffer than its own 6U counterpart, meaning it meets more rugged standards and is less vulnerable to shock and vibration.
Rear I/O has become an almost universal requirement in military applications because it provides different capabilities for different applications. The routing of board I/O signals to the backplane, either instead of, or in addition to routing them to the front panel, makes it much simpler to replace out in the field. The board itself can be considered a Line Replaceable Unit (LRU)–making maintenance simpler and less error-prone.
Overall, 3U CompactPCI has gained more popularity than its VME equivalent, thriving as its 3U form factor has kept up with the demand to reduce SWaP. In fact, with the range of processors on the market, it can have as much or as little power as needed. 3U CompactPCI is very widely supported and there is a broad range of rugged chassis available for this form factor. Lastly, if an older military system is already using CompactPCI, upgrades to the latest processors make an ideal replacement rather than moving to a new form factor.
The MicroTCA standard has risen in fact to address the issues of form factor and bandwidth. MicroTCA is characterized by high processing capacity, extremely high communication bandwidth and high availability designed into a small 2U form factor. Demands for SWaP considerations in mil/aero applications are all factored into MicroTCA’s 2U design. Initially developed for air-cooled telecom applications, MicroTCA still offers a NEBS Level 3 rating, making it rugged enough to withstand greater shock and the vibration of a major earthquake.
MicroTCA’s high bandwidth for both communications and computing is a direct result of up to 12 compute blades on a single backplane, which could potentially all use a multicore processor. A 3U or 4U system, for example, could have as many as 24 cores designed into MicroTCA’s very small footprint. MicroTCA designs can tap as many as 21 high-speed serial connections on the backplane, resulting in bandwidth of 2.5 Gbits/s for each connection. A broad range of communications bandwidth capacities is possible–ranging from 40 Gbits/s to over 1 Terabit/s–depending on how the system is implemented.
Many of the newest military initiatives for modernizing the battlefield rely on networks using standard Internet protocols. MicroTCA is potentially a good design choice for supporting these applications, because it offers native support for IP-based network topologies packaged with high bandwidth, increased computing power and the small form factor these network-centric applications require.
WIN-T, which is based on Internet protocols, is using the MicroTCA architecture in its networked systems. Networks appear just as any PC-based LAN being run in an office environment would, with each MicroTCA blade using a standard network connection. Because of this simplicity, the software development phase for MicroTCA is also much less complex than that of established VME or even standard CompactPCI architectures.
Even with SWaP concerns as a priority, computing bandwidth and high availability must be met. MicroTCA delivers a small form factor advantage over both VME and CompactPCI including their derivatives VITA 31, VITA 41 and PICMG 2.16. Systems benefit from the generally smaller MicroTCA blades, which also tend to use less power. Add multicore and MicroTCA’s processing power becomes even greater, even with a single backplane. 6U VME or CompactPCI designs can meet this bandwidth, but not when reduced to their smaller 3U form factors. MicroTCA is larger than the COM Express architecture, but with dimensions of 2U x 3-6HP x 183.5 mm, it is a smaller form factor than even 3U VME and Compact PCI.
Form Factor Choices Abound
Numerous options meet the bandwidth size, power and price point required for effective military designs. Being well versed in existing, new and evolving small form factors–along with the performance benefits and limitations they each bring to the table–is a way for designers to best understand the alternatives available to them in meeting the performance standards of any particular military application.