Scratchpad allocation for concurrent embedded software

Software-controlled scratchpad memory is increasingly employed in embedded systems as it offers better timing predictability com-pared to caches. Previous scratchpad allocation algorithms typi-cally consider single process applications. But embedded appli-cations are mostly multi-tasking with real-time constraints, where the scratchpad memory space has to be shared among interacting processes that may preempt each other. In this paper, we develop a novel dynamic scratchpad allocation technique that takes these process interferences into account to improve the performance and predictability of the memory system. We model the application as a Message Sequence Chart (MSC) to best capture the inter-process interactions. Our goal is to optimize the worst-case re-sponse time (WCRT) of the application through runtime reloading of the scratchpad memory content at appropriate execution points. We propose an iterative allocation algorithm that consists of two critical steps: (1) analyze the MSC along with the existing al-location to determine potential interference patterns, and (2) ex-ploit this interference information to tune the scratchpad reloading points and content so as to best improve the WCRT. We evaluate our memory allocation scheme on a real-world embedded applica-tion controlling an Unmanned Aerial Vehicle (UAV)