Abstract. 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 insu cient, because they do not provide exibility with respect to di erent target processors and also su er 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 approachtoachieve retargetability. We propose usage of uniform, external target processor models in code generation, which describe embedded processors by means of RT-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 di erent 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.

Besides high code quality, a primary issue in embedded code generation is retargetability of code generators. This paper presents techniques for automatic generation of code selectors from externally specified processor models. In contrast to previous work, our retargetable compiler Record does not require tool-specific modelling formalisms, but starts from general HDL processor models. From an HDL model, all processor aspects needed for code generation are automatically derived. As demonstrated by experimental results, short turnaround times for retargeting are achieved, which permits to study the HW/SW trade-off between processor architectures and program execution speed.

The concept of retargetability enables compiler technology to keep pace with the increasing variety of domain-specific embedded processors. In order to achieve user retargetability, powerful processor modeling formalisms are required. Most of the recent modeling formalisms concentrate on horizontal, VLIWlike instruction formats. However, for encoded instruction formats with restricted instruction-level parallelism (ILP), a large number of ILP constraints might need to be specified, resulting in less concise processor models. This paper presents an HDL-based approach to processor modeling for retargetable compilation, in which ILP may be implicitly constrained. As a consequence, the formalism allows for concise models also for encoded instruction formats. The practical applicability of the modeling formalism is demonstrated by means of a case study for a complex DSP 1 1 Introduction As a result of the increasing diversity of embedded processors, retargetable compilers have received re...