“In the end, it’s standards that create markets, not technology. This is why VME is still strong, because it is reliable and standardized,” says Ray Alderman, executive director of the VMEbus International Trade Association (VITA). When applications require modules with higher speed, performance, and bandwidth, developers have the option to use standard VPX (VITA 46) boards and deploy hybrid systems. They can take existing VME boards that don’t need a performance bump, like I/O boards, and mix them with high-performance VPX boards that can handle vast amounts of data, such as those from radar systems. Hybrid systems reduce the cost to transition to VPX because VME boards that are perfectly fine may be reused.

The VME installed base is predominately 6U, which will dictate the form factor for almost all VME/VPX hybrid systems. “I/O boards will stay VME in the future because they are usually low speed and moving them to a switching fabric would be unnecessary and possibly problematic,” explains David Pepper, single board computer technologist at GE Fanuc. On the other hand, 3U VPX systems—contenders for space-constrained environments like aircraft—are likely to be homogeneous because there are relatively few legacy 3U VME boards.

All Systems Go For VPX

“VPX is making great strides into the market with design wins in major programs. Today, many programs are even mandating the use of VPX,” says Jing Kwok, VPX Working Group Chair, VITA. He adds, “The standards are working well, Serial RapidIO and PCI Express fabrics are mapped in, and RF and optical connections are in the works.”

Giving the nod to VPX, General Dynamics C4 Systems and Rockwell Collins Inc. awarded an $8 million contract to Curtiss-Wright Controls to supply VPX modules for the U.S. Army’s Future Combat Systems (FCS) program. Perhaps the best indicator of hybrid acceptance comes from a backplane vendor. “There are a huge number of opportunities for VPX and it’s no longer a matter of education. Customers are coming with the desire for VPX, and we no longer need to evangelize,” states Robert Jadon, product manager at Curtiss-Wright Controls.

VME Isn’t Going Away

Despite being 27 years old, VME technology is still extremely popular. “It’s estimated that the VME market grew about 11% to 13% in 2007 and similar results are expected for 2008. The VME market demand is about 50% MIL/COTS with 25% in high-end industrial applications and 25% in all other segments including medical, transportation, and mining/drilling—among others,” says Alexander Buravlev, sales manager of Fastwel, maker of single-board computers and modules for mission-critical applications.

Figure 1: Here, VME single-board computers and blades are shown by architecture. (Source: Fastwel)

Many customers want to preserve the large investments that they made in legacy VME components. They like the idea of using hybrid systems, in which VPX addresses increasing performance requirements and VME handles the rest. It’s possible to gauge VME/VPX hybrid acceptance by looking at backplane demand. “We’re past the tirekicking stage and have been for some time now. I would say to date, at least more than half of the VPX-supported backplanes we sell have been hybrids. It’s certainly a big area,” explains Justin Moll, director of marketing at Elma Bustronic Corp. A photo of a hybrid backplane with five VPX slots and two VME slots is shown in Figure 2.

Figure 2: This hybrid backplane has five VPX and two VME slots. (Courtesy of Elma Bustronic)

Hybrids Reduce Cost And Risk

Because customers reuse dependable VME boards in hybrid systems, they save development costs while avoiding the risk of transitioning every system function to VPX at the same time. In addition, hybrids may require less expensive power-supply and cooling solutions than homogeneous VPX systems. After all, VME components typically consume less power than VPX. COTS chassis are typically modular designs. Constructing different sizes for various hybrid backplanes should therefore have a negligible impact on cost.

Down the road, customers can convert legacy VME modules to a smaller number of VPX modules and perhaps migrate from a 6U to 3U chassis. “VPX has the same number of pins as CompactPCI and many more than VME, so there’s a lot of available I/O. Suddenly, you have one board that does everything, so a lot of adjunct boards can be eliminated. And it’s relatively easy to implement the I/O on a PMC module, which is seated on a VPX board and takes advantage of the switch fabric,” emphasizes Joe Eicher, director of sales for military, aerospace, and government for the eastern North American region at Kontron.

Easing the transition to VPX, some board vendors will offer dual-track boards. “The same basic features and functions will be available in both VME and VPX form factors, supported by the same key components like bridges, OSs, BSPs, BIOS, and device drivers. Customers should be able to change over from VME to VPX with little or no software changes—a huge software savings,” states Frank Phelan, principal engineer at Kontron. Except for the pinout, the two designs have a lot of commonality with respect to board components and their placement.

A Symbiotic Relationship?

Although VPX and VME have substantial differences, hybrid systems are joining these two standards. This solution allows emerging functions—like transmitting the 1080p progressive scan format at 60 Hz—to run on VPX modules that have far more performance and I/O bandwidth than VME. At the same time, the rest of the system functions can be supported by legacy VME modules. This capability greatly reduces time to market and development cost.

Early on, there will be opportunities where VPX and VME product lines will collaborate. This combination will help VPX modules gain a foothold, as it won’t be necessary to design a whole system around VPX to take advantage of its performance. The ability to gradually migrate to VPX will ease its transition into existing applications. At the same time, hybrid systems may breathe new life into VME because VPX can overcome performance shortcomings. VPX technology could actually extend the lifetimes of some VME boards and even prompt the design of new boards.