TECHNOLOGY FOCUS VME SBCs for Tech Refresh
Refresh-Centric SBCs Keep VME’s Immortality on Track With VME still in the sweet spot for many military embedded computing systems, a continuous crop of refresh-centric VME SBCs offers the latest and greatest computing technologies. Jeff Child Editor-in-Chief
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ME has a rich and successful legacy in military systems in part because of its unique ability to remain backward compatible and facilitate technology refresh in military programs. A new board with the latest and greatest processor, memory and I/O can easily be dropped into a slot that could be decades old. Feeding that need, vendors continue to roll out new VME boards that sport the latest and greatest processors and memory technology. Since its introduction in 1981, the VMEbus standard has certainly satisfied the requirements of many defense systems. Successive generations of new processors provided more and more compute cycles, while VME bandwidth evolved in a similar fashion, from 40 Mbytes/s on the original VMEbus to 80 Mbytes/s, then 160 Mbytes/s, and finally 320 Mbytes/s on 2eSST. After a run of more than two decades, there weren’t any tricks left to squeeze more bandwidth out of the VME connector. The VXS standard (VITA 41), begun in March 2002 and ANSI-approved in May 2006, has extended the life of VMEbus, offering both increased bandwidth and a high level of board-level backward compatibility. Meanwhile, the VPX standard (VITA 46) or OpenVPX, emerged with a different set of characteristics for system bandwidth and backward compatibility. VPX is decidedly more aimed at high-bandwidth, data-intensive military applications. But there’s been a 64
COTS Journal | January 2012
Figure 1
The C-130 cockpit upgrade consists of a digital glass cockpit driven by mission computers based on open architecture VME rack systems. misconception as to how VPX is positioned versus VME in the market. As pointed out in VITA’s “2011 State of the VITA Technology Industry,” released last fall, to think of VPX as replacing VME is only a half-truth. VME is used in applications that are event-driven. These applications—controlling motors and actuators, moving gun turrets and missile launch-frames into position—are control system applications. VME’s interrupt structure is the only architecture that can handle these kinds of applications in real time. In contrast, other technologies such as fabrics and parallel PCI bus-based systems aren’t suited to meet those requirements. With that in mind, VME is expected to remain the primary architecture in these platforms for many years to come. Another aspect of VME that ensures its longevity is the fact that there are more than 400 programs in the military using VME.
And with the reductions in the DoD budget looming, VME upgrades and refreshes are much more likely to be funded, rather than forklift upgrades requiring new backplanes, packaging and power supplies. An example is the C-130 cockpit upgrade, which is comprised of a digital glass cockpit driven by mission computers based on open architecture VME rack systems (Figure 1). Adding a late-life kicker to VME, the VXS standard was developed to provide greater system bandwidth while maintaining enough backward compatibility to preserve the value of investments in VME board-level technology. VXS achieves this through an updated connector and the addition of a switch fabric architecture. With a VXS backplane, system engineers can also carry forward VME64 cards in payload slots without the need for a hybrid backplane.