VME and VPX Still Exist in Harmony

As a testament to the efforts of developing a clearly defined open standard, the OpenVPX standard has undergone very few changes or modifications since it was accepted and ratified by VITA in 2010 as ANSI/VITA 65-2010 (R:2012).

The changes made to the OpenVPX standard in 2012 (developed as VITA 65 OpenVPX) were made primarily to ensure better interoperability between boards from different COTS providers.  In reality, it merely corrected some document references and other minor errors, and more clearly defined Payload and Peripheral slots as well as and added a common reference clock, none of which radically altered the base VITA 46 2010 standard.

Figure 1: A 6U VME SBC

The latest revision, the first significant enhancement to the specification, addresses the increasing speed within an embedded system by adding features that accommodate high data processing speeds to meet the demands of data-intensive computing systems.

Simply put, VME has been the workhorse of the rugged computing industry for decades. It “has generated thousands of products and attracted hundreds of manufacturers of boards, mechanical hardware, software and bus interface chips. It continues to grow and support diverse applications such as industrial controls, military, telecommunications, office automation and instrumentation systems.” (source VITA: www.vita.com)

What Does My Application Require?
VPX itself serves a very different market segment than VME, and is particularly useful for high bandwidth applications, especially with the recent revisions. But it carries with it higher system integration requirements based on the complexity of the system, which adds significant costs as well as integration complexity. If your application needs to pass very high speed data across a backplane, then VPX is a good solution. However, if you don’t need all that bandwidth, then VPX, and its associated costs, could easily be overkill.

And because it has been around much longer, and does not include the complexity of the backplane profiles, VME has resolved many of its integration issues. Knowing the number of VMEbus backplane slots you will need is the most difficult issue you’re faced with when developing a VME system. On the other hand, you’re going to put in quite a bit more effort on the development side when specifying a VPX backplane.

What Problem Am I Trying to Solve?
Interestingly, in certain market sectors, new design wins for VMEbus are now roughly neck in neck with VPX. When you take into consideration the performance needs, cost constraints and the application requirements, the choice between VME or VPX will be pretty clear.

VME is still very popular in machine and process control systems, since it accomplishes the needed computing tasks and is far easier to implement, keeping costs down. Even in more rugged military applications, if you’re implementing a relatively simple process control function, like platform stabilization, missile fire control, AZ/EL “Slew-to-Cue” positioning, VMEbus remains a cost-effective solution that offers plenty of data processing horsepower.

Aitech’s Director, Military and Aerospace Product Management, Emil Kheyfets, noted, “With the large, diverse install base of VME, we need ways to utilize existing systems as well as incorporate upgraded electronics that meet the demands of today’s applications. Providing backward-compatible SBCs, like this C114, that can also keep pace with the growing data requirements, and provide a longer program lifecycle, preserves that infrastructure, while moving the industry forward.” See Figure 1.

However, when the system is processing “tons” of high speed data that’s being passed from one card to another in up- or down-stream, pre- or post-processing applications, VPX is definitely the way to go. Then you can look to boards like the high performance, Xeon-based C876.

Selecting VME or VPX doesn’t need to be an “either, or” situation. When evaluating the usability of both VME and VPX, take a look at which market sectors are actively using each for existing as well as new projects. Let the application dictate the solution.

Doug Patterson is VP, Military & Aerospace Business Sector, Aitech Defense Systems.

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