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38 connections, as shown in the table on the previous page, but type 6 with USB 3.0 CAN networking for control links and digital display interface (DDI) video connections is seen as a popular option for rugged embedded systems. Unlike the simpler low-voltage differential signal (LVDS) connections, the DDI connection can be adapted to DisplayPort, HDMI, DVI or SDVO in the carrier board. COM-Express types Also under development is a type 7, to support multi-core processors up to 16 cores and one, as yet unnamed type for higher bandwidth connections There are also different types of carrier board as standards have consolidated under the COM-E name: Mini: 55 × 84 mm (2.2 × 3.3 in), which was previously nanoETXexpress Compact: 95 × 95 mm (3.7 × 3.7 in), previously microETXexpress Basic: 95 × 125 mm (3.7 × 4.9 in), previously ETXexpress Extended: 110 × 155 mm (4.3 × 6.1 in) PC/104 was originally developed in 1987 to use the ISA bus from PC designs for embedded computing boards. The 90 × 96 mm boards are stacked on top of each other with processor, power, comms and I/O boards all with four mounting holes at the corners of each module. The overall height, weight and power consumption of the stack can vary depending on the number of boards used. The standard was updated in 1997 to add the PCI bus, and then again in 2008 to add the PCI Express bus for links that require a higher bandwidth. SMARC is a newer format, overseen by a group called the Standardisation Group for Embedded Technologies, for smaller boards using low-power processors for designs such as smaller UAVs. It uses the 314-pin connector from the MXM 3.0 format used for PCI Express mobile modules and graphics cards. This specifies a 82 x 105 mm card that is used for some autonomous driving systems with a higher performance, liquid-cooled board, but SMARC makes use of the connector on a smaller, 82 x 50 mm board. The latest version, SMARC 2.0, has ironed out some of the quirks of the original. It has removed some of the audio interfaces such as SPDIF and the parallel port, and added two more camera interfaces using the MIPI protocol. It also adds a fourth PCI Express Lane to provide a total bandwidth of 8 Gbit/s (4 x 2 Gbit/s). Obsolete interfaces such as the parallel ports for camera and display, the Alternative Function Block, off-module eMMC, SPDIF and one of three I2S low data rate control channels have been dropped as well.  At the same time, large chip makers are also producing their own board formats, particularly for small UAVs. They are mounting their processors on a small card to encourage UAV designers to use their connectors and pin-out specifications rather than standard cards. Conclusion The increasing processing demand for autonomous systems is creating a new focus on embedded boards and their form factors. The increasing performance of CPUs, GPU arrays and DSPs in silicon is in turn driving the need for higher bandwidth and new connector specifications, while system developers are trying to reduce the size and weight of the boards and not get trapped into one particular technology. With its ability to change the processor module and have customised carrier boards, COM-E type 6 allows developers to quickly produce a rugged embedded computing platform that is optimised for a particular application – whether it’s a UAV, driverless car or autonomous submarine. However, established rugged standards such as VPX and AMC are used increasingly in larger systems for their reliability and support for high- performance processors. At the smaller end there are several board formats available for different applications. A standard format allows developers to move more easily from one silicon device to another, enhancing the performance of the design without having to completely redesign it. Acknowledgements The author would like to thank Vincent Nguyen at Nvidia, Mark Littlewood at Kontron, Richard Edgar at Imagination Technologies, Christian Eder at Congatec and Saeed Karamooz at Vadatech for their help with researching this article. October/November 2016 | Unmanned Systems Technology Focus | Embedded computing Nvidia’s Jetson 2 board has been designed into autonomous ground systems as the central controller (Courtesy of Nvidia)