Lua-Based Virtual Machine Platform for Spacecraft On-Board Control Software

Abstract

Mission critical embedded software for autonomous operation requires high development cost due to its long development cycle. One of the potential solutions for reducing the cost is to reuse the software developed at previous missions. Virtual machine platform such as JVM is a good example to provide code portability across various missions. Flight software in aerospace field is adopting this concept to improve reusability and eventually to reduce development cost. In this paper, we propose a Lua-based virtualization environment for spacecraft flight software. Flight software for spacecraft control consists of a few tasks that are highly autonomous. Lua is chosen as the script language for programming the control tasks. Though Lua was designed with simplicity and portability, it only supports multithreading with collaborative coroutines. To support preemptive multitasking, we implement time slicing coroutines as spacecraft control processes. New coroutine scheduler is devised and time slicing functionality is added into the scheduler. Scheduler locking and message passing with external flight software are also implemented. Instead of modifying the Lua interpreter, we have exploited the debug support APIs for our implementation. For evaluation, we have implemented the flight software virtualization environment on the flight computer. Accuracy of the time slicing scheduler is also analyzed.