object, buffer and stack verification. This is important in an RTOS, as function pointers provide an easy path to unwanted program execution – both unintentional and intentional. For example, it is not good practice to place function pointers inside buffers, since a buffer overflow could also overwrite the function pointer. It’s also good to verify function pointers before they are used via a small hash or checksum. Function pointer corruption represents the easiest way for an attacker to initiate unwanted remote execution. As the RTOS is implemented with loosely coupled C functions, the size of the code automatically scales based on the application’s use. If the API and its associated functions are not used, they are simply not included in the code. The API consists of a native implementation of the Posix pthreads standard, which makes PX5 RTOS applications easily portable to any Posix pthread implementation, such as in Linux or even other RTOS implementations. However, there are always other requirements, so optional Posix pthread extensions are designed specifically for deeply embedded, real-time applications. Conclusion A separation kernel combines the capabilities of a real-time operating system with a hypervisor to allow different applications to run safely and securely in their own partitions, while still making use of the increased performance of the latest multi-core automotive processors. The scheduling capabilities of the RTOS allows safe and secure partitions for the real-time processing of Lidar point clouds and sensor fusion in driverless cars and UAVs. Extending an RTOS to a unikernel provides more scalability to reuse more types of software such as containers. Acknowledgements The author would like to thank Blll Lamie at PX5, Jose Almeida at Sysgo, Tim Loveless at Lynx and Dan Mender at Green Hills Software for their help with researching this article. 53 Uncrewed Systems Technology | December/January 2024 CANADA Mannarino Systems & Software (M-RTOS) +1 514 381 1360 www.mss.ca QNX +1 613 591 0931 www.blackberry.qnx.com FRANCE Adacore (GnatPRO) +33 1 49 70 67 16 www.adacore.com GERMANY Segger Microcontroller (embOS) +49 21 73 99 31 20 www.segger.com Sysgo (PikeOS) +49 6136 99480 www.sysgo.com JAPAN eSOL (eMCOS) +81 3 5365 1560 www.esol.com UK Amazon Web Services (FreeRTOS) – www.aws.amazon.com/freertos ARM (Keil RTX) +44 1223 400400 www.arm.com Wittenstein High Integrity Systems (SafeRTOS) +44 1782 286427 www.wittenstein.co.uk USA DDC-I (HeartOS, DeOS) +1 602 275 7172 www.ddci.com Green Hills Software (Integrity) +1 805 965 6044 www.ghs.com Linux Foundation (Zephyr) – www.zephyrproject.org Lynx Software Technologies (LynxOS) +1 408 979 3900 www.lynx.com Micrium (µC/OS) +1 954 217 2036 www.micrium.com Micro-ROS – micro-ros.github.io Microsoft (ThreadX) +1 858 613 6640 www.rtos.com NXP (MQX) +1 800 521 6274 www.nxp.com PX5 – www.px5rtos.com Siemens (Nucleus) – www.mentor.com/embedded- software/nucleus Wind River (VxWorks) +1 510 748 4100 www.windriver.com Examples of real-time operating system suppliers
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