Is there space for 3U and 6U VPX?
Will 6U VPX last as 3U choices emerge?
The small form factor VPX module uses switch serial fabric interconnects for more bandwidth without draining routing resources. It also offers increased power draw and more user I/O over VME.
“VPX is typically used in ISR (intelligence, surveillance, reconnaissance) used on small platforms, such as UAVs (unmanned autonomous vehicles) as well as manned vehicles where space is a premium,” says Richard Kirk, Director, Core Computing, at Abaco Systems. (The company was spun out of GE (General Electric) Intelligent Platforms in 2015.)
Generally, 6U modules are used for HPEC (High Performance Extreme Computing) in ground-based systems, large racks of equipment on navy ships or even large equipment to bring back data to process. Using a 3U VPX module in a UAV can bring size and weight advantages, which are critical for the vehicle’s mobility.
The longevity also means that there is a support system for designs. Nigel Forrester, Technical Product Marketing Manager, Concurrent Technologies, points out that 3U VPX is a trusted technology and therefore is “relatively risk-free, compared to other open standards.” “The key advantage of using 3U VPX,” he says “is the ability to source a wide choice of highly complex boards from the ecosystem.”
“It is not the smallest form factor,” he concedes, “but it is easy to construct solutions that are small enough to fit in manned aircraft, wheeled vehicles, medium and large unmanned vehicles (air, sea and land) and a variety of associated test, communications and control-based equipment, particularly those involved in surveillance, communications and electronic warfare.” The company has recently been involved in applications with low altitude, airborne image processing and anti-jamming tactical data link terminals.
The image processing application is based on 3U VPX Intel processor boards, combined with a GPGPU (General Purpose Graphics Processing Unit) board, and a solid state storage array for data archiving. “Using 3U VPX has enabled this application to be continually improved with the introduction of better processing elements without a change in the underlying box level solution,” he explains. The anti-jamming tactical data link terminal project is an example of the move away from older technologies to 3U VPX, says Forrester. It is implemented with a hybrid backplane, using a 3U VPX processor element, with some of the existing RF sensor and communications interfaces based on an older technology. “Over time, it is likely that more of the proprietary signal processing parts will migrate to VPX for longer life cycles,” he predicts.
The merits of 6U and 3U VPX
Scott Newland, Chief Mechanical Engineer, Airborne Electronics, Harris Corporation, advocates the performance characteristics of 3U VPX. “The primary benefits of 3U VPX are size, weight, improved thermal characteristics, and improved mechanical dynamic characteristics.” The company’s primary use of 3U VPX is in its sensor solutions. “Sensors with constrained resources, like unmanned air vehicles and small satellites are the primary benefactors”. While the processing power is similar in both formats, Newland notes that 3U has the advantage when it comes to processor performance per volume metric. “As processing fabric continues to become denser, the 3U VPX form factor has the potential to make inroads into the traditional 6U VPX market,” he believes.
Harris Corporation predominately provides 6U solutions for the traditional space markets. However Josh Bruckmeyer, Chief Technologist, Responsive ISR, Harris Corporation, remarks, “The small satellite market is one where we see 3U gaining a foothold. Typically these applications have shorter mission lives, lower budgets and can offer relief in the technology class/level requirements.”
Sensors with constrained resources, like unmanned air vehicles and small satellites are the primary benefactors.
The size of 3U VPX modules offers advantages other than space savings, as Nigel Forrester explains: “It is physically easier to ruggedize 3U based boards, compared to 6U equivalents. They can be made much stiffer, and the smaller real estate encourages designers to make more use of directly soldered components, such as memory.” The format also exploits parallel developments in silicon. “Modern chipsets offer ever increasing integration that makes it possible to fit more functionality onto a single board,” says Forrester. “This is important, especially for size- and weight-constrained equipment. . . a typical conduction-cooled 3U VPX board weighs roughly half that of a 6U board and this can equate to significantly better payload capacity in some target applications,” he says.
The same advances mean that the real estate capacity advantage of 6U is not as critical. “With the ever-increasing performance/Watt offered by modern processing devices, it is now possible to construct 3U VPX systems with the performance that was only possible in a 6U systems a few years ago,” maintains Nigel Forrester, citing the company’s recent introduction, the TR C4x/msd (Figure 2). This 3U VPX board is based on the eight-core Intel Xeon D-1500 family.
The choice of 3U or 6U can depend on ecosystem and support structure, as well as end use. “For small systems, with a heterogeneous architecture, 3U VPX is ideal,” maintains Richard Kirk. “There are many suppliers and a mix and match approach can be taken to get the ideal mix of GPU (Graphics Processing Unit), CPU (Central Processing Unit), FPGA (Field Programmable Gate Array) processing and I/O, such as ADC (Analog to Digital Conversion), graphics, 1553, and so on,” he says. “For larger systems, with a more homogeneous architecture, meaning the same features repeated many times – then 6U VPX comes into its own. Many 6U systems have multiple boards of the same type, building larger processing arrays, whereas 3U systems, usually (but not always) have a mix of boards.”
The density of a 6U format provides one advantage over 3U versions. One reason for the disparity is 3U VPX’s use of PCI Express. It is also more scalable, although the industry is addressing this shortfall, says Kirk. For larger systems, 6U VPX offers a tighter packing density than 3U VPX and is generally more scalable in that it usually features 10/40G Ethernet/ InfiniBand / SRIO (Serial RapidIO), as the fabric, which are designed for large arrays of nodes.” Richard Kirk, however, points out that companies, such as Abaco, have solutions to make PCI Express more scalable.
Another advantage that 6U VPX has over its 3U alternative, is more pins allocated to general I/O, allowing extra USB ports or boards to be added easily.
For Josh Bruckmeyer, the 3U module’s higher density packaging compared to the 6U form factor has some disadvantages, which bring financial penalties. “Dense packaging poses self EMI (Electromagnetic Interference) challenges, especially with RF performance parameters like channel-to-channel isolation,” he points out. “These complexities primarily drive the non-recurring engineering cost of product development. The impact to recurring cost is usually a second order effect, primarily being attributed to advanced materials and coatings,” he adds.
In space and satellite applications, there is room – and the need – for both 3U and 6U formats. It will be application-specific, says Charles Patrick Collier, Senior Electrical Research Engineer, Space Communications Program, Air Force Research Library, Space Vehicles: He believes the use of 3U and 6U VPX depends of the specific application space. Each application space will dictate its own requirements and this, in turn, will dictate the type and number of boards used, and what topology is used in a design flow. “The choice does not seem to be split evenly between 3U and 6U,” says Collier. “The commercial market is seemingly walking a path toward 3U VPX over 6U VPX, given the benefits of 3U VPX over 6U, with respect to thermal management, etc.”
Opportunities for Customization
As an open standard, there are opportunities for customization of 3U VPX boards. Nigel Forrester says that Concurrent Technologies takes the view that off-the-shelf products will mix easily alongside customized ones. “Where 3U VPX is appropriate, our view is that as many off-the-shelf building blocks will be adopted as possible, and that over time, customization will be through add-on modules rather than complete boards.” He proposes one option would be for customers to provide their own front-end signal conditioning using the FMC (FPGA Mezzanine Card) module concept or add their own PMC (PCI Mezzanine Card)/XMC (Switch Mezzanine Card) module for specific I/O functionality.
VITA 78.1 SpaceVPX Specification
In October 2015, the US Army’s IT and integrated systems center, CERDEC (Communications-Electronics Research, Development and Engineering Center) joined VITA. It will develop VPX for some architectures for mobile devices, tank and personnel carriers that require open, rugged, lighter systems.
The primary benefits of 3U VPX are size, weight, improved thermal characteristics, and improved mechanical dynamic characteristics.
Design teams want an open architecture to interchange computer systems and with a large ecosystem for choice and support, says Jerry Gipper, Executive Director, VITA. The VITA 75 specification defines the system, but there was no guidance from the VITA Standards Organization (VSO) of how to move forward with embedded computing that will be cost-effective for space electronics. In April 2015, the VSO ratified VITA 78 “SpaceVPX” Systems, an open standard to create fault-tolerant, interoperable backplanes and modules to assemble electronic systems for spacecraft and other high-availability applications in aerospace as well as terrestrial projects.
Since ratification, the Association has proposed VITA 78.1, which is designed to focus on 3U implementation of the VITA 78 specification. Gipper says that it is hoped that VITA 78.1 will be completed by the end of 2016.
“A primary feature of SpaceVPX Lite is the reduction and distribution of the SpaceVPX SpaceUM (Utility Management) functionality,” says Josh Bruckmeyer. “SpaceVPX Lite introduces a PowerSX construct, where each PowerSX module switches main power for up to eight modules. This essentially distributes the power switching functionality of one 6U module to three 3U modules,” explains. By simplifying the SpaceUM module, Bruckmeyer believes that SpaceVPX Lite may aid in the general adoption of SpaceVPX. This simplification of the SpaceUM should decrease the drive for customization, he adds.
Caroline Hayes has been a journalist, covering the electronics sector for over 20 years. She has edited UK and pan-European titles, covering design and technology for established and emerging applications.