Vertical object layout and compression for fixed heaps

Abstract

Research into embedded sensor networks has placed increased focus on the problem of developing reliable and flexible software for microcontroller-class devices. Languages such as nesC [8] and Virgil [14] have brought higher-level programming idioms to this lowest layer of software, thereby adding expressiveness. Both languages are marked by the absence of dynamic memory allocation, which removes the need for a runtime system to manage memory. To provide data structures, nesC offers modules, and Virgil offers the application an opportunity to allocate and initialize objects during compilation. This paper explores techniques for compressing fixed object heaps with the goal of reducing the RAM footprint of a program. We explore table-based compression and introduce a novel form of object layout called vertical object layout. We provide experimental results that measure the impact on RAM size, code size, and execution time for a set of Virgil programs. Our results show that compressed vertical layout has better execution time and code size than tablebased compression while achieving more than 20% heap reduction on 6 of 12 benchmark programs.