Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

30 Focus | Real-time operating systems the software – its kernel – has as little code as possible, with the bare minimum of functionality, to allow its functions to be clearly defined and certified, and to provide as small an attack ‘surface’ as possible to hackers. With a secure and certified kernel though, other elements can be securely added on top to provide a trusted stack. The aircraft industry has led the way with this technology, with the ARINC 653 (Avionics Application Standard Software Interface) specification for separating software applications in time and space. The idea behind ARINC on an RTOS is very conservative, that during a minor timeframe all it is doing is running the scheduler with single time slots until there is a full context switch from one application to the next – the time separation. While this means the application performance isn’t affected, the overhead is in the switching process, erasing the old data and loading in the new. This requires a cache flush, memory management unit (MMU) reconfiguration or a full memory swap. Most system software designers do a full cache flush in the context switch to clear out any residue information, but that brings with it a processing overhead; the guarantee it gives though is full performance for the application while it is running, and that’s a huge benefit for an unmanned system. There is also a drive to add on operating systems such as Windows or Linux. This hasn’t been an issue in the past, but with more mapping data and sensors being used in unmanned systems there can be applications and algorithms that use this software. For example, open-source UAV autopilot systems use Linux to integrate automatic take-off and landing, telemetry, dead-reckoning navigation and Google Earth, and in an open-source environment user-specific code can be added, making for lower-cost development. Most of the work in an RTOS is around security, secure boot-up and safe operation. Using multiple processing cores (multicore) on a single chip can provide significant advantages here. From an RTOS point of VxWorks from Wind River has been used for a variant that supports the ARINC 653 real- time software specification The software’s kernel has as little code as possible, to provide as small a hacking attack ‘surface’ as possible November 2014 | Unmanned Systems Technology