Taking the VPX ecosystem to the next level
StoryOctober 27, 2009
Justin Moll
Pixus Technologies
The VPX industry needs to add more test/prototype and development tools to its ecosystem, and careful consideration of modules, cooling methods, and subsystem integration is also necessary in furthering the high-speed architecture's ecosystem.
There are several elements to an architecture’s ecosystem, including development products, deployable products, test tools, and related services. Imagine how much time can be shaved off project development times with specific devices for a specified form factor that aid prototyping/testing and development. Without devices such as load boards, RTMs, and development systems, the systems engineer is forced to use less accurate alternatives. When development is quicker and easier, a larger amount of products can be brought to market more efficiently. This in turn creates a cyclical churning that encourages higher adoption rates (with cheaper and more accurate products), more development, and so on.
During the past few years, the VPX architecture has seen an accumulation of boards, chassis, and backplanes to provide more choices for the customer. However, an architecture needs more to thrive. As mentioned, without adequate development systems and testing/prototyping tools, development can be hindered. Thus, the VPX ecosystem also needs these important elements. Cooling methods and subsystem integration are also vital considerations linked to the VPX ecosystem.
Development systems
Development chassis are a key part of the ecosystem, as they provide a rugged enclosure for prototyping and testing. They will often have top carrying handles for portability and rugged or scratch-proof covers to survive demos, shows and events, or lab use. However, as VPX card wattages continue to increase, the development chassis needs to evolve with it. This includes having higher-power options for larger VPX backplanes. Some of these development chassis will need power supplies exceeding 1,300 W, and the enclosure will need to adequately cool the higher-wattage cards.
More fans with higher Cubic Feet per Minute (CFM) may be required in these development chassis. Take, for example, a five-slot VPX backplane in a small portable chassis with protective covers, and 2 x 190 CFM fans. (If this were a VME64x architecture, it would have just a 1 x 90 CFM fan.) Then consider an open-frame chassis designed specifically for VPX. To handle the more intensive power and cooling requirements, this unit has 3 x 170 CFM fans and a 1,300 W power supply often used for larger VPX backplanes. With a small backplane, the five-slot chassis was modified with the more robust fans to cool a VPX design. For larger backplanes, a design (like the open frame version) allowing more fans with high CFMs is likely a necessity for adequate cooling.
To make a development chassis simpler and more cost-effective, a two-slot 6U VPX backplane implementation is needed. The backplane would allow point-to-point signals between the slots and its flexible design would ensure compatible use with a large amount of VPX boards. A small backplane like this with fewer slots and layers could also help provide a useful way of prototyping/testing boards without a large expense. The small size would make it easier to provide power and cooling, thus reducing costs as well. A two-slot VPX backplane is in development.
Going hand-in-hand with the development chassis is the extender board. VPX extender boards are coming out in both 3U and 6U versions. These allow the signals to be extended outside of the card cage for easier test and debugging. This is particularly important for the immediate adjacent cards in the system. As the mating right-angle connectors are not available in the market for plugging the VPX cards into the extender, a rigid-flex-rigid design can overcome the problem.
Test tools: Proof of performance
Test and debug is an important part of the design process and the more testing/prototyping tools the industry can provide for VPX, the better. With the performance of VPX, the design engineer will witness lots of power, and plenty of heat. Thus, VPX systems must be carefully simulated and tested. The VPX ecosystem has been short of these types of signal performance testing tools.
SERDES test modules: “The health monitor”
However, one tool that will help facilitate the goal of building the VPX ecosystem is the VPX SERDES test module: a pluggable 6U VPX card that acts like a health monitor, checking the “vital stats” of the VPX system. In minutes, a designer or tester can check the Bit Error Rate (BER), jitter, skew, and so on – and execute pattern generation such as eye diagrams for the signals. It can be used to test a VPX board, a VPX backplane, or the full interconnect path between boards across the backplane.
Load boards: Power ‘em up
Another beneficial tool for VPX is a load board. It can aid the system designer in assuring adequate chassis cooling and verifying that the VPX chassis is capable of meeting the power requirements of the system (or VITA specs). The load board functions to test a system’s cooling capabilities by first applying the load to the power supply for verification and creating the necessary heat to confirm chassis cooling. By helping the test engineer locate hot spots in the chassis, he can verify where to optimally redirect the airflow to prevent overheating (see Figure 1). The load boards can be designed in either 3U or 6U versions. Without a load board, the test engineer simply could not test the system at various wattage load levels and make necessary adjustments to the system.
Figure 1: A VPX load board allows the test engineer to step up the voltages and power levels as desired to apply various loads for testing.
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Important VPX considerations: RTMs and cooling
Development and testing products are very important for the VPX ecosystem. But the standard chassis and backplanes need some creative solutions too, like RTMs.
RTMs ease I/O
Also a viable consideration affecting the VPX ecosystem is the Rear Transition Module (RTM), which brings I/O off a backplane in a pluggable format. Otherwise, designers need to use ribbon cable or wire wraps that are less reliable, not designed for rugged use, and so on. However, an RTM for VPX can be designed for various configurations of the J0-J6 connectors, and a version designed as a Universal VPX RTM break-out board can allow a test engineer to access I/O signals on custom-built VPX boards. The board would not be intended for high-speed multigig differential signals but would typically be used to bring out single-ended TTL signals that might be part of a customer’s custom I/O board. (Figure 2 illustrates this type of interface.)
Figure 2: A Universal VPX RTM board can have open connections out the back for directly wiring any pin.
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Development with conduction/liquid cooling
In addition to the aforementioned metrics and considerations for the VPX ecosystem, cooling is imperative to VPX’s market proliferation. Whether using 3U or 6U high cards, typical VPX wattage per slot today is 100-120 W and rising. Therefore, enclosures need to cool these chassis in creative ways, especially in densely packaged designs. With applications such as UAVs, forced-air cooling may not be an option due to lack of available air in the enclosed design or in high altitudes. Conduction cooling can be effective, but conduction alone typically cannot dissipate the 100-120+ W levels. VITA 48 will provide a pathway to liquid cooling through the individual modules.
Although progress is being made in the VITA 48 specification, there is more work to be done. The VPX community needs a cost-effective way to develop higher-wattage conduction-cooled boards. One solution in the meantime is to have the liquid go through the chassis sidewalls. This can provide up to 150 W per slot of cooling, without the tricky issue of having the liquid go through each card. This alternative is more than adequate for many applications – and is a highly simplified and cost-effective design consideration.
Summing it all up: Fostering the VPX ecosystem
From the already-present VPX boards, backplanes, and chassis to the still-needed development and test tools to the RTM, cooling, and subsystem integration considerations, the VPX ecosystem needs to continue to grow. This in turn will make a design and test engineer’s life easier and provide superior VPX solutions in the industry.
Justin Moll is director of marketing at Elma Bustronic, where he has worked since 2000. He is active in VITA and PICMG and has been the VP of marketing for the StarFabric Trade Association. He received his Bachelor of Science degree in Business Administration from the University of California, Riverside. He can be reached at [email protected].
Elma Bustronic 510-490-7388 www.bustronic.com
