MMU없는 내장형 시스템의 메모리 사용량을 줄이기 위한 주 정적 공유 라이브러리 기법

Abstract

Embedded systems are quite often subject to severe resource constraints, and this presents extreme design challenges for developers. Despite a rapid decrease in the price of solid state memory devices, system memory is still a very precious resource in such systems. The use of shared libraries is known to be effective in significantly reducing memory usage. Unfortunately, many resource-constrained embedded systems lack MMU, making it extremely difficult to support these techniques. To address this problem, we propose a novel shared library scheme called the quasi-static shared library. In quasi-static shared libraries, global symbols are bound to pseudo-addresses at linking time and the actual physical addresses are bound at loading time. This scheme is made possible by emulating MMU’s memory mapping feature with a Data Section Base Register (DSBR) and a Data Section Base Table (DSBT). Quasistatic shared libraries do not require symbol tables which take up time and space at runtime. We have implemented the proposed scheme in a MMU-less embedded system. We measured its memory usage and evaluated its performance overhead by conducting a series of experiments. These experiments clearly demonstrate the effectiveness of our scheme in reducing the memory usage. The result is drastic: a 35% reduction in flash memory usage and a 10% reduction in RAM usage. These results were achieved with only a negligible performance penalty of less than 4%.