Knots: An Efficient Single Stack Preemption Mechanism for Resource Constrained Devices

The low-end embedded systems space is characterized by two classes of operating systems: run-to-completion (RTC) systems such as TinyOS and preemptive multithread- ing systems such as Mantis. In RTC systems only a single task may exist on the stack at any time, therefore RTC sys- tems have low memory requirements for the stack space but have poor deadline handling capabilities. Preemptive mul- tithreading systems are better at deadline handling but all tasks in the system require memory for their worst-case exe- cution stack at all times. This results in suboptimal amount of memory allocation for the system. The two types of sys- tems define the two end points of a spectrum characterized by varying degrees of deadline handling capabilities and memory requirements. We have designed and implemented a system that by efficiently performing preemption on a sin- gle stack offers the flexibility of operating anywhere on this spectrum. It also offers improved deadline handling capa- bilities than RTC systems and lower memory requirements than preemptive multithreading systems.