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44 Focus | Embedded computing PC/104e Many unmanned systems, particularly for underwater systems and UGVs, were designed with PC/104 cards. These stackable cards measure 90 x 96 mm, and the standard was agreed back in 1992, with four corner mounting holes to provide resistance to shock and vibration with a 0.600 in (15.24 mm) stacking height and stand-off tolerances. There is also a version with a 0.866 in stacking height The latest PC/104 Express (PC/104e) format can use the same self-stacking form factor and the same connector to the I/O and sensors but adds the PCI Express interface to support newer processors with faster memory. The key factor is that the newer processors add features such as TPM2.0 that provides security, although the additional performance is limited by the thermal properties of the PC/104 system, so this tends to be for Intel Atom- class processors rather than the Core i3 class. This allows the system to be upgraded to newer versions of embedded operating systems with increased safety and security features and more memory. The PC/104e connector supports four PCIe channels with automatic detection of up- or down-stacking and automatic link-shifting to allow simplified, universal add-on sensor boards Like COM Express, there are larger form factors to fit more onto a board, with EPIC Express and EBX-Express as versions of the PC/104 Consortium’s EPIC and EBX form factors. Both PCIe/104 Type 1 and Type 2 have a common feature set and pin assignments, with four x1 PCI Express Links and two USB 2.0 interfaces, and uses power and control signals for ATX power supplies. Type 1 PC/104e boards add a x16 PCI Express Link that can be configured as two x8 links or two x4 PCI Express links, depending the host. Type 2 boards have two x4 PCI Express links with two USB 3.0 interfaces and two SATA interfaces for hard drives. February/March 2022 | Unmanned Systems Technology One of the key emerging standards for embedded systems in larger unmanned vehicles is OpenVPX. This is an open version of the VPX standard that superseded the earlier VME card standard to add PCI Express, hence VME PCI X. The standards for VPX are driven by the VMEbus International Trade Association (VITA) working group that includes the major embedded systems developers as the VITA46 standard. This uses the same 3U and 6U sizing as VME but with a seven-row high speed connector rated at up to 6.25 Gbit/s It also adds PCI Mezzanine Card (PMC) and XMC mezzanines (PMC with high- speed serial fabric interconnect) cards that can be laid on top. There is a wide range of VITA standards for the many different aspects of embedded cards. For example, the Ruggedised Enhanced Design Implementation (REDI) in VITA 48 describes how to implement layout techniques to better support cooling methodologies on specific board form factors. It currently covers enhanced forced- air cooling (using baffles and plenums), advanced conduction cooling (using larger and more efficient thermal interfaces) and liquid cooling. VITA 46.30 defines a higher data rate VPX connector for 25-plus Gbit/s rates to enable PCIe Gen 4 serial comms and 100GBase-KR4 Ethernet while maintaining mating compatibility with legacy VITA 46 connectors. VITA 67.3 (RF modules) is being revised to add options for higher density coaxial interfaces. These support two to three times the density of the legacy designs that started with VITA 67.1 and 67.2. VITA 66.5 defines blind-mate fibre optic interconnections for VITA 46 backplanes and plug-in modules, and brings the capability for mounting transceivers directly on the edge of the plug-in board (within a VITA 66 module frame) to save space on the board.   A 3-MT (mechanical transfer) half-size module is being incorporated into this standard to improve the optical density. In addition, the floating insert design used for alignment in both NanoRF and VITA 66 optical modules allows for integrating RF and optics into a common connector module for additional density. The OpenVPX Systems Specification, VITA65, defines an architecture framework that manages and constrains module and backplane designs, including defining pin-outs, and sets interoperability points within VPX while maintaining full compliance with VPX. It is being adopted by SOSA (see sidebar: The Sensor Open Systems Architecture). SOSA is standardising on several RF, optical, and RF/optical combination connector module configurations in specific profiles and will be documented in VITA 65.0 and 65.1, which define the slot profiles and associated interconnect. For external connections between boxes, SOSA is adopting military-standard solutions, such as Mil-Dtl-38999 rugged circular connectors. But the need for higher density copper and optics at the panel has driven SOSA to also use VITA standards such as VITA 76 circular copper interconnections and VITA 87 for a rugged circular connector with high-density optical interfaces. OpenVPX A 6U 19 in rackmount chassis for 3U OpenVPX- and SOSA-aligned boards supports up to 16 conduction-cooled modules to meet SOSA requirements and VITA 48.2 specifications (Courtesy of Pixus Technologies)