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46 Model-based design A key trend in the development of embedded systems is the move to model- based design. Tools such as Simulink are used to build complex control models for autonomous systems, with code being generated automatically from the model to run on an embedded board. One tool, the QGen code generator from Adacore, takes a subset of Simulink blocks and automatically produces code that accurately reflects the model. This tool is being qualified to the TQL1 safety standard for DO-178C oriented aerospace projects to significantly reduce the amount of manual verification that needs to be done on the resulting code. This is a challenging process. Simulink is a rich, growing modelling language developed by Mathworks and it can be difficult to produce code that can be certified for use in safety-critical systems such as unmanned systems. The heart of developing a reliable, trustworthy automatic code generator is defining every piece of Simulink, including which blocks in the subset that could be used with the code generator to produce a safe and certifiable output. Starting with 100 of the most commonly used blocks, this has been extended to 120 after working with aerospace, automotive and industrial system designers. This has led to the development of additional tools around the code generator. The first is a checker to assess whether the blocks a designer is using will work with the code generator. A model will be rejected if it doesn’t fit the subset, but the February/March 2022 | Unmanned Systems Technology As sensor systems increase in number, the applications, cost and complexity faced by embedded systems developers increases the challenges on cost and usability. The Sensor Open Systems Architecture (SOSA) Consortium, set up by the Open Group, enables government and industry to collaboratively develop open standards for affordable, interoperable and rugged sensor systems that can be rapidly reconfigured and easily reused. SOSA is creating open system reference architectures for the US military and commercial sensor systems in a range of embedded formats for airborne, subsurface, surface, ground and space systems. The architectures use a modular design with non- proprietary standards for key interfaces, and this is also driving adoption in Europe for a range of designs in commercial unmanned developments. Edition 1.0 of the technical standard for the SOSA Reference Architecture was released in September 2021, after five years of development. The Open Systems Architecture (OSA) addresses software, hardware and interfaces across comms systems, EO/IR imaging systems and radar for developing reusable sensor components applicable to a broad class of sensors and host platforms. The SOSA approach allows ‘capabilities’ to be developed as components that are exposed to other components through well-defined interfaces. It also provides for the reuse of SOSA modules across different environments, with a module having a core set of mandatory functionalities but different variants that can be developed over time, as different systems can have different additional characteristics such as special environmental conditions, higher throughput, higher reliability and so on. The specification is initially based around 3U or 6U boards that can be used in a backplane with plug-and- play capabilities using standards such as OpenVPX (see sidebar: OpenVPX). The boards can have data processing with CPUs, GPUs or FPGAs, Ethernet networking, radio processing or memory storage with data capture cards and cards to manage the chassis. The point of OSA is that it allows cards from different manufacturers to be used in the same chassis with common software. The SOSA standard needs to consider a wide range of processing environments as realised by the selection of processors, operating systems, network protocols, backplanes, memory architectures and comms circuits. That means the interfaces are independent from the processing environment through abstraction. The SOSA architecture also provides the building blocks for deriving multiple sensor types that scale within a design, increasing or decreasing complexity relative to processing and SWaP constraints for a host platform. Normally this is a vehicle, aircraft or ship with a combination of one or more sensor pods, delivering power, cooling, platform navigation information such as position and velocity as well as reference signals for clocks or timing. It also includes the network connections and connections for any other analogue or digital interfaces. For example, Annapolis Micro Systems is combining its 3U and 6U FPGA boards and switch modules capable of 10 Gigabit Ethernet with modular open systems approach-based single-board computers and digital signal processor engines from Curtiss-Wright. The SOSA hardware specification working group has unofficially started a Small Form Factor group that will focus on the extension of the SOSA Architecture to form factors used in UAVs, UGVs, UUVs and small satellites. The Sensor Open Systems Architecture