Retargetable code generation based on structural processor descriptions

Design automation for embedded systems comprising both hardware and software components demands for code generators integrated into electronic CAD systems. These code generators provide the necessary link between software synthesis tools in HW/SW codesign systems and embedded processors. General-purpose compilers for standard processors are often insufficient, because they do not provide flexibility with respect to different target processors and also suffer from inferior code quality. While recent research on code generation for embedded processors has primarily focussed on code quality issues, in this contribution we emphasize the importance of retargetability, and we describe an approach to achieve retargetability. We propose usage of uniform, external target processor models in code generation, which describe embedded processors by means of PT-level netlists. Such structural models incorporate more hardware details than purely behavioral models, thereby permitting a close link to hardware design tools and fast adaptation to different target processors. The MSSQ compiler, which is part of the MIMOLA hardware design system, operates on structural models. We describe input formats, central data structures, and code generation techniques in MSSQ. The compiler has been successfully retargeted to a number of real-life processors, which proves feasibility of our approach with respect to retargetability. We discuss capabilities and limitations of MSSQ, and identify possible areas of improvement.