Complex instruction and software library mapping for embedded software using symbolic algebra

With growing demand for embedded multimedia applications, time to market of embedded software has become a crucial issue. As a result, embedded software designers often use libraries that have been preoptimized for a given processor to achieve higher code quality. Unfortunately, current software design methodology often leaves high-level arithmetic optimizations and the use of complex library elements up to the designer's ingenuity. In this paper, we present a tool flow and a methodology, SymSoft, that automates the use of complex processor instructions and preoptimized software library routines using symbolic algebraic techniques. We use SymSoft to optimize a set of examples for the SmartBadgeIV (Maguire et al., 1998) portable embedded system running the Linux embedded operating system. The results of these optimizations show that by using SymSoft we can map the critical basic blocks of the benchmark examples to the StrongARM SA-1110 instruction set much more efficiently than the commercial StrongARM compiler. SymSoft is also used to map critical code sections to commercially available software libraries with complex mathematical elements such as exp or the inverse discrete cosine transform routine. Our measurements on SmartBadgeIV show that even higher performance improvements and energy savings are achieved by using these library elements. For example, the final optimized MP3 audio decoder runs four times faster than real-time playback while consuming four times less energy. Since the decoder executes faster than real-time playback, additional energy savings are now possible by using processor frequency and voltage scaling.