Inter-Task Energy-Hotspot Elimination in Fixed-Priority Real-Time Embedded Systems

Multitask real-time embedded systems are often restricted by tight energy budgets, whilst they usually have environmental interactions through software-controlled energy-hungry peripheral modules, such as LTE, WiFi, and GSM. The way that the driver calls are used within the embedded software to do such a control introduces program energy-hotspots (EHs) from the peripheral module perspective, namely, the code pieces wasting the system energy. By the energy waste, we mean that the energy consumption is reducible via some program code modifications without threatening the system schedulability and logical correctness. This article examines the program EHs of fixed-priority real-time tasks where two types of energy inefficiency can occur: 1) intra-task type, causing energy waste even if a task runs individually and 2) inter-task type, happening due to the interaction between different system tasks, namely, preemption scenarios even if there is no intra-task EH. The main cause of such EHs is the unnecessary time intervals between the driver calls, causing extra energy consumption by peripheral modules. We propose some static analysis methods to automatically detect and eliminate both types of intra- and inter-task EHs regarding their mutual relevance, according to the extreme (worst-case and best-case) execution times of certain task code parts. Our manipulations on the tasks to eliminate the EHs include some program code modifications with the awareness of system schedulability and logical correctness, and changing some scheduling decisions, namely, limiting the preemption points. After applying our proposed method to the test tasks, our simulation results show an energy reduction of up to 19%.