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13.1 Introduction

The Code Generation (CG) domain and its derivative domains, such as the CG56 domain (Motorola DSP56000) and the C language (CGC) domain, are used to generate code rather than to run simulations. Only the derivative domains are of practical use for generating code. The stars in the CG domain itself can be thought of as "comment generators"; they are useful for testing and debugging schedulers and for little else. The CG domain is intended as a model and a collection of base classes for derivative domains. This section documents the common features and general structure of all code generation domains.

All the code generation domains that are derived from the CG domain in this release obey SDF semantics and can thus be scheduled at compile time. Internally, however, the CG only assumes that stars obey data flow semantics. Currently, we have implemented two approaches for data-dependent execution, CGDDF, which recognizes and implements certain commonly used programming constructs [Sha92], and BDF ("Boolean dataflow" or the token-flow model) [Buc93c]. Even when these are implemented, the vast majority of stars in any given application should obey the SDF rules to permit efficient multiprocessor code generation.

A key feature of code generation domains is the notion of a target architecture. Every application must have a user-specified target architecture, selected from a set of targets supported by the user-selected domain. Every target architecture is derived from the base class Target, and controls such operations as scheduling, compiling, assembling, and downloading code. Since the target controls scheduling, multiprocessor architectures can be supported with automated task partitioning and synchronization.

Another feature of the code generation domains is the ability to use different schedulers. A key idea in Ptolemy is that there is no single scheduler that is expected to handle all situations. We have designed a suite of specialized schedulers that can be mixed and matched for specific applications. Some targets in the CG domain, in addition to serving as base classes for derived domains, allow the user to experiment with these various schedulers.

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