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36 as COM-E and SMARC. Many of these are actually defined by the bandwidth and protocols of the interconnect as well as the physical dimensions of the boards, although moves are growing to standardise on the PCI Express protocol used in PCs. One challenge for system designers is that embedded boards will have a long lifetime in many autonomous system designs, and so need support for seven to ten years – even longer for driverless cars. That restricts the range of boards and processors that can be used to the ones that suppliers are willing to support in the long term. VPX is a 3U and 6U board specification that emerged from the VME standard to provide more bandwidth across the backplane, and the development is overseen by the VITA standards group as the VITA 46 standard. It is used in defence applications such as the large Predator and Global Hawk UAVs, where there is a demand for computing performance for synthetic aperture radar and complex surveillance. The processor cards can support multiple devices, each with up to 16 processor cores, and sit in a chassis connected to the I/O cards via a high- speed backplane. The biggest difference between VME and VPX boards is the connector. VPX uses a MultiGig RT2 connector, with six 16-column seven-row connectors and one eight-column seven-row connector on a 6U card, or two 16-column seven- row connectors and one eight-column seven-row connector on the 3U card. The number of connectors of course determines the maximum bandwidth for the card, as each connector supports transfer rates up to 6.25 Gbit/s. That gives a 6U VPX board a total of 707 non- power electrical contacts and a total of 464 signal contacts. Current bandwidth on the backplane is 10 Gbit/s per port, but there are suppliers working on 20 and 40 Gbit/s. Researchers are even working on 100 Gbit/s per port which, with typically 32 ports on a backplane, gives terabit/s levels of bandwidth. While this level of performance will be limited to static installations, the improvements in the chips to support those speeds will reduce the power consumption of the 10 Gbit/s and 20 Gbit/s links, making them more attractive for large autonomous systems. High-performance embedded processors require large amounts of power, so with VPX the power available has been boosted to 384 W at 12 V or 768 W at 48 V. This brings with it the need for more cooling, and the Ruggedised Enhanced Design Implementation VITA 48 specification describes how to lay out the boards for different cooling methodologies such as forced, natural air or even liquid cooling. The VPX specifications are focused at the board level, but there is also a need for considering system-level requirements to improve interoperability and reduce customisation, testing, cost and risk. The OpenVPX systems specification (VITA 65) therefore defines an architecture framework for module and backplane designs, including defining pin-outs, and sets out where it can be used with VPX. Another approach has been to take a commercial board standard and October/November 2016 | Unmanned Systems Technology Examples of embedded computing boards Kontron VPX VX305x – 100 x 160 mm Vadatech AMC529 – 75 x 180 mm Kontron COM-Express Compact – 95 x 95 mm The boards will have a long lifetime in many autonomous systems, so they will need support from suppliers for up to ten years