Even before it’s official ratification in December 2017, VITA 74, or VNX, had been rapidly gaining traction for a number of distinct embedded computing markets. The need for this standard was two-fold.
First, designers of small form factor (SFF) systems needed a way to make sense of the fact that the well-known form factors just weren’t going to cut it anymore as component density increased, package size decreased, and thermal management concerns kept rising.
Next, as the industry embraced a more compact computing structure, end users were still looking for the interoperability and modularity they’d come to expect in the larger, standards-based systems. The same principles of cohesion and cost-consciousness still applied.
Many old timers may recall the early days of embedded computing, where an altruistic concept was created, then thrown to the industry with some loose parameters, resulting in multiple ‘standard’ versions of the same computing concept. Hence the proliferation of well-defined platforms, such as 19” rack mount systems, 3U and 6U Eurocard, VME and later VPX-based systems, etc.
As SFFs emerged, they fractured the notion that systems needed to adhere to commonly-accepted 1U, 3U, 6U, etc. dimensions. This SFF industry fragmentation, instead, needed a method of adopting a means of moving these high-performance systems forward in a way that would benefit the industry as well as the individual companies involved.
Repurposing the Wheel, Not Reinventing It
While addressing these needs, VNX draws from certain tried-and-true concepts of the more mature VPX standard as well as leveraging many successful System on Module (SOM) form factors widely in use in the commercial and military marketplace. At the same time, it incorporates the necessary adaptations to make VNX applicable for these applications where SFF computing is required.
This allows the standard to capitalize on a mature market and knowledgeable user base. VNX provides the means and structure to build its own community to construct low cost, high reliability SFF systems with minimal investment and risk.
Below is a quick highlight of some aspects of VNX. A more detailed overview, a downloadable reference design and other supporting information is available at the VITA VNX Community page.
Some commonalities:
- Power supply: VNX systems use the same PSU voltages and controls as found in a typical VPX system.
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I/O: As in a typical VPX system, requisite signals are routed from the backplane to the system’s exterior via an I/O Transition Board (IOTB). The IOTB is typically a printed wiring board (PWB) that functions as the connector panel for I/O as well as providing test interfaces, signal filtering and pin hardening.
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Backplane: Like VPX, the VNX module slot profile is divided into three main sections: a utility plane; a serial fabric plane; and a user I/O plane, which allows electrical connections from each module slot to interconnect to other slots and modules.
Main differences:
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Size: VNX currently includes two module dimensions, 12.5 mm (single board or highly compact two board stack) and 19 mm (typically a two board stack), both much smaller than its VPX-based counterparts.
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Structure: Using guide pins and the module’s connector, the module is mated directly to the backplane and is typically held in place by the chassis’ mechanical assembly. This eliminates the need for wedgelocks to secure the module in place.
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Thermal management: The two side faces and handle face of each VITA 74 module are outfitted with the proper Thermal Interface Material (TIM) between the chassis side walls and back panel. A small gap between modules provides for reasonable manufacturing tolerances and easy module removal.
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Module Insertion and Removal: A typical VNX system requires that the access panel be removed and the adjacent side panels be loosened to insert and remove the VNX module. Wedgelocks, as used in VPX, are not required in the base standard.
Maturity Even at the Early Stages
Although it’s been less than a year since VITA 74.0 was officially ratified, it boasts a well-worn path of adoption and implementation. From the ground up, VNX was designed to take maximum advantage of other tried and true technologies, borrowing the electrical topology directly from VPX and the connector family from the FMC standard, while using dimensions from other industry standards such as COM Express and Mini PCI Express.
VNX brings with it several proposed ‘dot’ specifications that will increase the usability and robustness of this recently-minted VITA standard to address specific marketplaces and applications.
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ANSI/VITA 74.0-2017 (VNX): Ratified base standard
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VITA 74.1: (Reserved)
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VITA 74.2: Rear transition module standard
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VITA 74.3: Set of slot profiles for CPU, I/O, storage and other specific modules that will define pin assignments and signal characteristics to enhance VITA 74 module interoperability.
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VITA 74.4 (SpaceVNX): Additions to VITA 74.0 that will enable use in high reliability and high availability avionic and flight control applications, as is the case with space applications. Modeled after VITA’s in-process “SpaceVPX-Lite”.
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VITA 74.5: VNX with an optical connection. Will bring optics through the backplane using the existing VNX connector with adjacent auxiliary MT Ferrule.
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VITA 74.6: VNX with one or more RF connections. Will bring RF through the backplane using the existing VNX connector with adjacent RF connectors, as well as to provide standard for bringing RF from the front of the module.
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VITA 74.7: Will facilitate high-performance cooling and packaging utilizing chassis-mounted wedgelocks with VNX baseline modules for higher power applications, when needed.
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VITA 74.8: Will describe connector standardization for a VNX system Power Supply Unit (PSU) and Filter & Hold-Up Module, both implemented in a 19mm module, utilizing the functionality found in the VITA 62 PSU standard often utilized in VPX systems.
The Evolution Continues
Not only does VNX provide a solid foundation for building the initial stages of standardized SFF computing, it is designed with technology reuse, upgradability and economies of scale as well. It offers higher reliability than other COTS adaptations, such as PC/104, which does not inherently have ruggedization capabilities. It’s basis in VPX gives VNX that conduction cooled and rigid structure that makes it ideal for military, mobile, and space environments.
The VNX standard addresses the need for a unified approach to small-scale systems to be used in a variety of MIL-Rugged applications. It encourages multiple vendors to supply components to be used in SFF systems at various levels; i.e., modules, mezzanine boards, backplanes, enclosures and complete solutions, with the goal of enabling vendor implementation flexibility, while at the same time, maximizing component interoperability.
Companies that develop VNX products are encouraged to contact VITA to join the VNX Marketing Alliance, comprised of technology suppliers developing products based on the VNX standard.
