Here’s what you should know about ANSI/VITA-74 and its role in small form factor systems including Mission Computers, Display Processors, Signal Concentrators and Data Storage Units for the avionics, vetronics, and space markets.
Choosing the technology which best addresses SWaP considerations challenges system architects developing rugged computers for the mil-aero market, even as we continue to do more with less. For example, System-on-Chip (SoC) technologies make it easier to add capabilities such as high-performance video, Ethernet, and I/O support on a single chip (rather than on separate boards), thus saving size and weight. Similarly, employing high-performance and high-reliability System-on-Module (SoM) technologies makes it less expensive and, more important, less risky, to develop new and smaller embedded systems. However, the availability of solutions like those just mentioned that step up to SWaP demands doesn’t relieve system architects of their responsibility to choose from among a number of Small Form Factor or SFF architectures. 3U VPX? PC/104? mTCA? Proprietary? And this choice must also take into account the preference in the mil-aero sector for using standards, i.e., PICMG, VITA, ANSI, based equipment. The use of standards-based equipment has been shown to provide better interoperability and drive down costs by allowing more suppliers to meet the market demand with COTS products.
3U VPX—The First-Generation Small Form Factor
More than 10 years ago, 3U VPX was officially introduced to the embedded systems marketplace as a response to the growing demand for smaller computers requiring ever-increasing processing power. 3U VPX in its most recent form, OpenVPX, (ANSI/VITA-65), has become the de facto standard for new projects where SWaP is an issue and qualification to very severe military and commercial standards is mandatory. VITA is an incorporated, non-profit organization that is a “Who’s Who” of vendors, integrators, and users with a common interest in real-time, modular embedded computing systems. The VITA Standards Organization (VSO), the standards development arm of VITA, is accredited as an American National Standards Institute (ANSI) developer and a submitter of Industry Trade Agreements to the International Electrotechnical Commission (IEC). VITA provides members with the ability to develop and to promote open technology standards.
After VPX, the marketplace is still encouraging manufacturers to shrink the size and increase the density of standards-based rugged embedded computing platforms, further optimizing the SWaP proposition for SFF systems. Several companies developed ways to accomplish these goals, and VITA started three different SFF working groups to study and develop different approaches to the smaller size/greater density demands. Viewed from an integrated system perspective, only one standard bubbled to the top; VITA 74. For compatibility and ease of adoption, the VITA 74 committee borrowed the architecture that made OpenVPX successful and imported it into the new standard in its entirety. This committee also adopted technology from other successful standards for backplane connectors, intra-system connectivity, processor mezzanine boards, and I/O modules to specifically reduce development risk, cost, and time to market. The outcome was ANSI/VITA 74, better known as VNX.
VNX (ANSI/VITA-74) Makes the Most of Lessons Learned
A COTS module standard for SFF applications, VNX was developed by members of VITA to be conduction-cooled and extremely rugged. As such, the standard is a suitable platform for the Single Board Computers (SBCs), Signal Processors, and I/O Modules found in integrated systems. Utilizing Modular Open Systems Architecture (MOSA) principles, VNX provides the first standards based, slotted module approach to very small conduction-cooled SFF systems. The baseline VNX standard is officially known as ANSI/VITA 74.0-2017.
VNX developers brought proven technology and “lessons learned” from as many existing standards as practical to the new standard, minimizing economic, technical, and schedule risks:
- The electrical signal interfaces and system topology for VNX is derived directly from VPX (VITA 46) and OpenVPX (VITA 65). The VITA 74.0 electrical signaling and PCI Express (PCIe) data bus structure is identical to that specified in VITA 65. Module slot profiles are being developed from the outset in a manner similar to VITA 65.
- The VNX connector is a derivative of the FMC (VITA 57) connector; the same connector series, but with a slightly different contact arrangement. This connector, the Samtec SEARAY™, has been thoroughly qualified and shown to be operable to PCIe Gen3 speeds and beyond, making it a natural fit for high-speed data bus, video, storage and even RF connections.
- Many VNX SBC modules use PICMG “COM Express Mini” Type 10 processor mezzanine boards mounted on a VNX carrier inside a VNX mechanical shell, further reducing time to market, risk, and cost. Other “non-standard” mezzanine modules with similar electrical and mechanical attributes are available from a variety of rugged embedded module manufacturers, bringing forward compute modules employing Intel, Power, Arm and FPGA SoC/SoM architectures, which can be easily utilized in a VNX SBC module.
- Many VNX I/O modules utilize another PICMG standard, Mini PCI Express (MiniPCIe). MiniPCIe and identically sized mSATA modules have been integrated onto VNX carriers, allowing myriad existing COTS I/O and storage modules from many different vendors to be used in a VNX inspired system.
For SWaP critical and price sensitive applications, VNX provides the flexibility of the VPX specification in a smaller form factor; resulting in reduced size, weight, and power consumption, oftentimes at a lower cost.
The ANSI/VITA 74.0 base standard defines physical and electrical features on the VITA 74 compliant system plug-in module which enable reliable fit and function in a compliant system. The standard defined two module sizes; a 78mm x 89mm x 19mm module (Figure 1) and a 78mm x 89mm x 12.5mm module, both similar in size to a deck of ordinary playing cards, and both with well-defined high-speed differential and single ended signaling. The electrical differential, single-ended, power and maintenance connections are defined in the base standard. The base standard includes an implementation of an inter-module data bus, PCI Express. The PCI Express fabric acts as the main conduit for module to module signaling within a system.
The base standard also defines module alignment and keying features used to protect the connector system. The plug-in modules can only be oriented in one direction when being inserted into a slot. This keying is implemented in the module mechanical shell, its associated slot guide, the connector and its counterpart on the backplane.
All VITA 74 compliant Plug-In Modules, backplanes, and systems incorporate the following major features defined in the standard:
- Module and backplane connectors
- Keying and alignment mechanism for all slots
- Support for the VITA 74-defined power rails VS1, VS2, VS3, VS4
- Support for the VITA 74-defined utility signals including the Geographical Address pins, PCIe Reference Clocks, System Management signals, Non Volatile Memory Read Only (NVMRO) signal, SYSRESET*, Reserved Bussed signals, and provisions for Reserved for Future Use (RFU) single ended signals
- Fabric provisioning for one or more of the various protocol layer standards, including the Base protocol, PCIe As part of the VITA 74 standard committee’s work, a reference design was generated, providing mechanical design elements for a typical 4-slot chassis, including a chassis, backplane, front panel and payload modules as shown in Figure 2. For purchasers of the standard, this reference information can serve to shorten time to market for new VNX deployments.
The VITA 74 Family of Standards
There are several VITA 74 “dot standards” that have been identified and are in various phases of work. These standards currently include:
- ANSI/VITA 74.0: The baseline VITA-74 “VNX” standard describing modules that may be used to build an SFF rugged system. In VPX parlance, this standard is similar to ANSI/VITA 46 and ANSI/VITA 65.
- VITA 74.1: A standard for a complete stand-alone, self-contained, full-function computer module, roughly the size of a deck of cards.
- VITA 74.2: A standard for a VITA 74.0 Rear Transition Module (RTM).
- VITA 74.3: A standard to collect and centralize various VITA 74.0 compatible SBC and I/O Module Slot Profiles. In VPX parlance, this standard will be similar to VITA 65.
- VITA 74.4: Also known as SpaceVNX, this standard is being written to aid VNX modules’ use in space applications. SpaceVNX is similar in scope to VITA 78’s “SpaceVPX Light.” This committee is currently developing architectures that combine RAD-hard monitors and controls, redundancy management, and COTS processing and I/O hardware to define a RAD-tolerant system architecture suitable for use in CubeSATs and other small satellite and space-based mission electronics.
- VITA 74.5: A standard that is being developed to bring many lanes of Optical data through the VNX backplane. One current approach is to use a multi-lane MT connector adjacent to the copper connector to accomplish this feat.
- VITA 74.6: A standard that is being developed to bring several RF connections on coaxial interfaces adjacent to the copper connector.
- VITA 74.7: A standard that is being developed to allow a compliant VNX module to be used in a higher power, higher performance, chassis with improved cooling characteristics, employing wedge locking devices that are mounted in the chassis, not on the module, thus allowing standard VNX modules to be used in systems with and without wedgelocks.
- VITA 74.8: A standard that is being developed to bring the Power Supply technologies found in VITA 62 to the VITA 74 family, using a smaller but similar connector, power supply voltages, and control signaling.
Application examples which utilize the VNX standard are rolling out for airborne, ground vehicle and space applications. An example of a “VNX 1+2” system containing one 19mm SBC sites and two 12.5mm I/O sites, plus two sites for a power supply and hold-up modules, is shown in Figure 3.
Brame Technologies, Trident Infosol, Samtec and its partners are co-sponsors and developers on the VITA 74 Technical Committee, as well as participants on the VNX Marketing Alliance. Bill Ripley holds the chairman position for the VITA 74.0 Technical Committee; a group that met regularly to bring the VNX standard to fruition, consisting of multiple suppliers, integrators and customers who are embracing and building hardware and systems which support and utilize the VITA 74 family of standards.
Bill Ripley is an Electrical Engineer and Business Development professional with over 35 years of experience in the avionic / military embedded computer market. For the first half of his career, Bill worked in a major helicopter / tiltrotor manufacturer’s system integration organization, followed by the second half working for COTS module and M-COTS system providers. Bill has been active participant in the VITA Standards Organization, Vehicle Integration for C4ISR/EW Interoperability (VICTORY) standards committee, the Future Airborne Capability Environment (FACE™) community, as well as the European analog of VICTORY, the MILVA & NGVA groups. Currently, Bill is the founder of Brame Technologies working with various hardware providers and integrators in the Small Form Factor system business, supporting the MIL-Aero and Space communities.