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.

Due to the large variety of different embedded processor types, retargetable software development tools, such as compilers and simulators, have received attention recently. Retargetability allows to handle different target processors with a single tool. In this paper, we present a system for automatic generation of instruction set simulators for a class of embedded processors. Retargetability is achieved by automatic generation of simulators from processor descriptions, given as behavioral or RT-level HDL models. The presented system is capable of bit-true simulation for arbitrary processor word lengths, and it generates both interpretive or compiled simulators. Experimental results for different processors indicate comparatively high simulation speed. 1 Introduction Today, the core functionality of many embedded systems is implemented by software running on embedded programmable processor cores, while dedicated ASIC hardware is mainly used for accelerating the execution of time-criti...

retargetable compilers, table-driven compilers, machine description, processor description, instruction-level parallelism, EPIC processors, VLIW processors, EPIC compilers, VLIW compilers, code generation, scheduling, register allocation In the past, due to the restricted gate count available on an inexpensive chip, embedded DSPs have had limited parallelism, few registers and irregular, incomplete interconnectivity. More recently, with increasing levels of integration, embedded VLIW processors have started to appear. Such processors typically have higher levels of instruction-level parallelism, more registers, and a relatively regular interconnect between the registers and the functional units. The central challenges faced by a code generator for an EPIC (Explicitly Parallel Instruction Computing) or VLIW processor are quite different from those for the earlier DSPs and, consequently, so is the structure of a code generator that is designed to be easily retargetable. In this report, we explain the nature of the challenges faced by an EPIC or VLIW compiler and present a strategy for performing code generation in an incremental fashion that is best suited to generating high-quality code efficiently. We also describe the Operation Binding Lattice, a formal model for incrementally binding the opcodes and register assignments in an EPIC code generator. As we show, this reflects the phase structure of the EPIC code generator. It also defines the structure of the machine-description database, which is queried by the code generator for the information that it needs about the target processor. Lastly, we discuss general features of our implementation of these ideas and techniques in Elcor, our EPIC compiler research infrastructure.

Interest in synthesis of Application Specific Instruction Processors or ASIPs has increased considerably and a number of methodologies have been proposed in the last decade. This paper attempts to survey the state of the art in this area and identifies some issues which need to be addressed. We have identified the five key steps in ASIP design as application analysis, architectural design space exploration, instruction set generation, code synthesis and hardware synthesis. A broad classification of the approaches reported in the literature is done. The paper notes the need to broaden the architectural space being explored and to tightly couple the various subtasks in ASIP synthesis.

This dissertation presents a set of techniques for representing the high-level behavior of a digital subsystem as a collection of nondeterministic finite automata, NFA. Desired behavioral and implementation dynamics: dependencies, repetition, bounded resources, sequential character, and control state, can also be similarly modeled. All possible system execution sequences, obeying imposed constraints, are encapsulated in a composed NFA. Technology similar to that used in symbolic model checking enables implicit exploration and extraction of best-possible execution sequences. This provides a very general, systematic procedure to perform exact high-level synthesis of cyclic, control-dominated behaviors constrained by arbitrary sequential constraints. This dissertation further demonstrates that these techniques are scalable to practical problem sizes and complexities. Exact scheduling solutions are constructed for a variety of academic and industrial problems, including a pipelined RISC processor. The ability to represent and schedule sequential models with hundreds of tasks and one-half million control cases substantially raises the bar as to what is believed possible for exact scheduling models. Keywords: Scheduling; Binary Decision Diagrams; High-Level Synthesis; Nondeterminism; Automata; Symbolic Model.

The increasing use of programmable processors as IP blocks in embedded system design creates a need for C/C++ compilers capable of generating efficient machine code. Many of today's compilers for embedded processors suffer from insufficient code quality in terms of code size and performance. This violates the tight chip area and realtime constraints often imposed on embedded systems. The reason is that embedded processors typically show architectural features which are not well handled by classical compiler technology. This paper provides a survey of methods and techniques dedicated to efficient code generation for embedded processors. Emphasis is put on DSP and multimedia processors, for which better compiler technology is definitely required. In addition, some frontend aspects and recent trends in research and industry are briefly covered. The goal of these recent efforts in embedded code generation is to facilitate the step from assembly to high-level language progra...

Embedded systems present a tremendous opportunity to customize designs by exploiting the application behavior. Shrinking time-to-market, coupled with short product lifetimes create a critical need for rapid exploration and evaluation of candidate architectures. Architecture Description Languages (ADL) enable exploration of programmable architectures for a given set of application programs under various design con-straints such as area, power, and performance. The ADL is used to specify programmable embedded systems including processor, coprocessor and memory architectures. The ADL specification is used to generate a variety of software tools and models facilitating exploration and validation of candidate architectures. This chapter surveys the existing ADLs in terms of (a) the inherent features of the languages; and (b) the methodologies they support to enable simulation, compilation, synthesis, test generation, and validation of programmable embedded systems. It concludes with a discussion of relative merits and demerits of the existing ADLs, and expected features of future ADLs. 1

Modern Embedded Systems-on-Chips (SOCs) will allow the system designer to customize Intellectual Property (IP) cores (fixed and programmable), together with custom logic and large amounts of embedded memories. As the software content in these emerging embedded SOCs begins to dominate the SOC design process, there is a critical need for support of an integrated software development environment (including compilers, simulators and debuggers). Furthermore, since many characteristics of these processor core IPs (e.g., instruction-sets, memory configurations) are increasingly customizable, the entire software toolkit chain needs to be customized and generated to support both early design space exploration (for performance, power and cost constraints), as well as high-quality software generation. This paper first surveys recent efforts in Architecture Description Languages (ADLs) used to perform early validation and exploration of SOC architectures. The second part of the paper focuses on ap...

Performance estimation is a crucial operation which drives the design space exploration in Application Specific Instruction Set Processor (ASIP) synthesis. With the increase in the level of integration, the design space has considerably expanded which makes the simulation driven techniques inadequate due to their slow speed. Alternatively, there are approaches which estimate performance by scheduling the application on the available processor resources without generating code. These are much more effective in exploring a large design space.

In this paper we report a framework that makes it possible for a designer to rapidly explore the application-specific programmable processor design space under area constraints. The framework uses a production-quality compiler and simulation tools to synthesize a high performance machine for an application. Using the framework we evaluate the validity of the fundamental assumption behind the development of application-specific programmable processors. Application-specific processors are based on the idea that applications differ from each other in key architectural parameters, such as the available instruction-level parallelism, demand on various hardware components (e.g. cache memory units, register files) and the need for different number of functional units. We found that the framework introduced in this paper can be valuable in making early design decisions such as area and architectural trade-off, cache and instruction issue width trade-off under area constraint, and the number of branch units and issue width.