EMPRESS:an efficient and effective method for PREdictable stack sharing

Stack sharing between tasks may significantly reduce the amount of memory required in resource-constrained real-time embedded systems. On the downside, stack sharing decreases the predictability of a system, e.g. may give rise to a substantial variation in the address space for the memory locations used for the stack of a task. As a result, the precisionof execution-time bounds may be reduced, the pessimism inschedulability analysis increased, and optimizations to increaseschedulability hampered. In this paper, we present EMPRESS, an Efficient and effective Method for PREdictable Stack Sharing. We assume priority-based scheduled systems, where the binary pre-emption relationon tasks is a strict partial order, and static bounds on each task’sstack usage. Both assumptions are common in the embedded real-timedomain. For such systems, EMPRESS provides a predictable stack sharing between tasks, i.e. the stack of every task is always located in the very same memory area, even for tasks sharing a stack. It therefore combines the predictability of dedicated stack spaces with the reduced memory need of a shared stack. We exemplify the benefits of EMPRESS using as a case study an implementation of an unmanned aerial vehicle, and explain howEMPRESS can be realized within the Erika Enterprise RTOS without additional overheads