RTC Magazine

VME has enjoyed robust growth since it was adopted in 1981. Today the merchant VME board market is north of $1B and growing at a respectable clip. In aerospace and defense, nearly 80% of the merchant boards procured are VME. Furthermore, VME is expanding in this market at nearly 8% CAGR for the foreseeable future. There is a perception that VME is in retreat in commercial markets, but this is not entirely the case. Electronic Trends Publications forecasts growth in VME in the industrial computing market at more than 7% CAGR through 2010.

Interestingly, despite much merger and acquisition activity, the top players in the VME merchant market have remained relatively stable. Table 1 shows the top VME board vendors. Mercury was named the top VME board vendor for 2005. VME has enjoyed continual renewal as newer and better technologies are added to it in an evolutionary fashion. Over the past 25 years, the data transfer rate over the tried-and-true DIN connector has increased by an order of magnitude; the latest innovation being VME320. VME64x added a fabric connector that further increased inter-slot data rates. VME’s success has partly depended on having maintained backward compatibility at the pin level.

VXS (VITA 41) vs. VPX (VITA 46)

The most recent tension in the VME market relates to VXS (VITA 41) and VPX (VITA 46). Some customers are concerned the market is bifurcating. They are right! The market is bifurcating, but not in the way that is commonly thought. VXS and VPX actually have a great deal in common.

Figure 1 shows the typical architecture of a sensor computer used in a radar or signals intelligence application. The system has a radio frequency module to transmit and receive signals, an A/D board, a quad-processor card, and a single-board computer with dual-mezzanine I/O slots. The boards are interconnected with a high-speed fabric that is depicted using a fabric switch card.

In the software domain, there is system software, data movement middleware, numeric libraries such as VSIPL and of course, the user application. Note that this canonical system is form-factor-agnostic. It could be VXS. It could be VPX. It could be something else completely. All of these form-factors use the same basic technological ingredients: PowerPC, RapidIO, Linux, etc. In fact, Mercury has demonstrated families of products based on VXS, VPX-REDI, AdvancedTCA, CompactPCI and other form-factors—all based around a common processor/fabric/software architecture. With a single underlying software and hardware architecture, the ultimate form-factor deployed can reflect an application designer’s needs and preferences in mechanical robustness and ecosystem.

VXS – VPX Differences and Similarities

The mechanical differences in VXS and VPX are fairly straightforward if you read the standards. The differences are summarized in Table 2. VXS is exactly like VME64, maintaining the P0 and P2 connectors, but adds an improved P0 connector that supports modern multi-GHz serial fabrics like RapidIO. With a VXS backplane, system engineers can carry forward VME64 cards without the necessity of a hybrid backplane. Note, the VXS P0 obsoletes the VME64x P0. This is a difficult development for VME64x customers who are now coping with the fact that the leading VME64x fabric silicon company appears to no longer be a growing concern.

Unlike VXS, VPX is a ground up redesign of the backplane chassis. VPX can support VME, but does not mandate that VME be carried forward. It eliminates the VME P1 and P2 DIN connector in favor of the new multi-GHz connectors. As shown in Table 2, it has much greater I/O pin capacity. When teamed up with the REDI standard (VITA 48), the result is truly revolutionary, supporting higher slot power budgets, enhanced ruggedization and allowing for an array of open-standard cooling methodologies: liquid flow through and liquid spray in addition to conduction and air.

It’s natural to think that VXS and VPX will compete with each other if you focus only on the mechanical differences between them. In reality, they complement each other. This can be understood only if we examine the ecosystems of the respective standards. Each standard addresses a different set of application requirements—one “demanding” and the other “extreme.”

Over time, system designers will always gravitate toward the simplest solutions possible. For example, if a single Pentium motherboard running Linux will solve a problem at hand, why look further? If the application is fairly straightforward, designers will typically select a benign solution (Figure 2). Benign applications are generally stationary, run in temperature-controlled environments, require one or only a few processors and modest connectivity. These solutions play an important function in the overall ecosystem by setting a baseline for price and performance. Further, they improve relentlessly, forcing competing solutions to follow a similarly aggressive continuous improvement curve.