Interoperability key to adoption of VITA and PICMG standards in military, aerospace marketStory
December 08, 2014
VITA and PICMG are the open standards bodies that define the specifications underpinning embedded form factors such as VPX and CompactPCI. Both groups continue to provide a vital service to commercial off-the-shelf (COTS) component manufacturers and customers alike, enabling engineers to spend less time worrying about interoperability between subsystem components and more time working on application development.
Let us consider a defense company embarking on a new radar design. Here are three common scenarios faced by the system integrator:
Assembling the first prototype of a new product
The budget and timeline have been agreed upon and VPX has been selected as the form factor. Subsystem blocks are to include multiple A/D and D/A converter modules, FPGAs for heavy-duty processing of the incoming data, and a single-board computer (SBC) to control the system as a whole.
Along with power-supply units, storage elements, and the chassis itself, all of these components are available as COTS products. With a wide range of vendors for each component, however, how can the engineers responsible for integrating the system be confident that each of these boards will be mechanically and electrically compatible, operate within a power budget, and be able to communicate with each other?
The answer, of course, is that each of these COTS products is compliant with VITA 46 and shares a common slot profile from the OpenVPX standard. Based around a high-speed switched interconnect, the VITA 46 (VPX) and the complementary VITA 65 (OpenVPX) standards provide a framework on which to design a new product, enabling designers to focus more of their energy on the real value of their product. For example, without worrying about interoperability, manufacturers of FPGA boards can concentrate less on the trivial aspects of the board such as pinouts and the polarity of reset signals and more on the intricacies of FPGA configuration, memory interfacing, and implementing DMA engines. An SBC manufacturer can worry less about the mechanical profile of its board and more on exposing the latest features of the chosen processor. The system integrator can be confident that I/O voltages will be compatible, transmit and receive channels will align, and that the boards will be able to communicate.
Inherent to this interoperability is reduced time to market and lowered costs in comparison with custom solutions.
Upgrading the product
The first prototype has been a wide success, but silicon developments mean that the chipset is now inferior to what’s offered on the current commercial market and an upgrade is required. In a custom system, this would necessitate a complete redesign due to ingrained device footprints and arbitrary I/O allocation. Having designed to the VPX standard, however, the system integrator is able to simply swap out boards containing outdated FPGAs, CPUs, or A/D devices and replace with the latest offerings from the various VPX vendors. Open standards bring flexibility and the ability to take advantage of technology improvements.
Changing the form factor
A potential new customer has emerged but with tighter size, weight, and power (SWaP) requirements. Thanks to open standards, much of the original system can be reused. With many vendors producing variations of their boards in different form factors, the system components and key algorithms can remain the same; once again the mechanics, electrical characteristics, and pinouts are guaranteed to work together.
Throughout the whole product life cycle, open standards encourage competition and provide opportunities for large and small manufacturers alike (see Figure 1).
Figure 1: Thanks to open standards such as VPX, COTS products from various manufacturers can easily be combined in a final system. (Image courtesy of Alpha Data.)
(Click graphic to zoom by 1.9x)
Use of mezzanines in open standards
One of VITA’s moves was the development of VITA 42, the XMC standard. XMC – the acronym for switched mezzanine card – inherits the physical sizing of the common mezzanine card (CMC) but adds support for switched interconnect standards such as PCI Express and RapidIO.
Measuring just 149 mm x 74 mm, XMCs can be plugged into PCI Express, CompactPCI, and VPX carriers. This ability to span a number of different architectures is advantageous during the early phases of defense projects. Before the final system is assembled, firmware and software engineers can begin development in a familiar desktop setup using XMCs plugged into a PCI Express carrier. This practice is particularly prevalent where FPGAs are involved, enabling engineers to gain a foothold in the use of the FPGA manufacturer’s tools. Importantly, the same XMC can now be deployed in the final chassis-based system, whether that is VPX, CompactPCI, or another embedded architecture.
A number of vendors offer SBCs and FPGA cards in the XMC form factor. Alpha Data offers a range of XMCs featuring Xilinx Virtex 5, Virtex 6, and 7-series FPGAs, which can be ordered as individual units or preassembled on a 3U VPX carrier (see Figure 2).
Figure 2: Alpha Data’s ADA-VPX3-7K1 is a Xilinx Kintex-7 based XMC preassembled on a 3U VPX carrier.
(Click graphic to zoom by 1.9x)
VITA 57, the specification for FMC (FPGA mezzanine card) is similar to XMC in that it can be plugged into larger form factors. The key difference with the FMC standard is that the focus is on adapting the I/O of the carrier module’s FPGA, whereas the FPGA or CPU, whichever it is, is found on the XMC itself.
Both of these standards share that key ingredient to success in the military/aerospace market – interoperability. Due to the effort of the contributors to the VITA 42 and VITA 57 specification and their various sub-specifications, XMCs and FMCs can be plugged in and out of different systems like Lego bricks, changing the function of the system entirely. Such interoperability means that x86 processors can be swapped out for hybrid FPGA-ARM “system-on-chip” (SoC) devices, DSPs can be replaced by mass storage devices, and upgrades to denser silicon devices is straightforward.
While the likes of VPX, XMC, CompactPCI, and MicroTCA have gained a strong foothold in the military market, work on a trio of competing rugged small form factors is in full swing. VITA 73, 74, and 75 are all in the “Draft Standard for Trial Use” phase of development. While which of these the market will adopt remains to be seen, one thing we can be sure of is that interoperability between modules from numerous vendors will be vital to their success.
It’s clear that the open-standards movement has made a sizable dent in the historically inflexible defense market. VITA and PICMG standards provide opportunities for board vendors to capitalize on their individual strengths, whether in processors, FPGAs, or any other common component in modern embedded systems. The bonus for system integrators: flexibility throughout the whole life cycle of their product.
Lewis Allison is a design engineer at Alpha Data Parallel Systems Ltd, a provider of high-end FPGA COTS products. He received a Masters of Engineering in Electronics and a Bachelors of Electrical Engineering degree from the University of Edinburgh. Readers may contact him at [email protected].