Modular Code Generation from Synchronous Block Diagrams: Interfaces, Abstraction, Compositionality

We study abstract, compositional and executable representations of synchronous models in general and hierarchical synchronous block diagrams in particular. Our work is motivated by the problem of modular code generation, where sequential code (in, say, C or Java) must be generated for a given block independently of its context, that is, independently of the diagrams in which this block may be embedded. We propose non-monolithic interfaces called profiles as a representation of blocks. A profile contains a set of interface functions that implement the semantics of the block, and a set of dependencies between these functions. Profiles are executable through the implementation of their interface functions. Profiles are compositional in the sense that a diagram of profiles can be represented as a single profile without loss of important information, such as input-output dependencies. This is contrary to traditional methods which use monolithic interfaces that contain a fixed number of interface functions, usually just one or two. Monolithic interfaces generally result in loss of input-output dependency information and are non-compositional. Profiles are abstract in the sense that they hide most of the internal details of a diagram (e.g., functionality). We provide methods for profile synthesis and modular code generation: to automatically produce profiles and profile implementations of composite blocks, given profiles of their sub-blocks. Our work reveals fundamental trade-offs between the size and reusability of a profile, as well as between characteristics of the generated code and complexity of the synthesis algorithms. We discuss various algorithms that explore these trade-offs, among which algorithms that achieve maximal reusability with optimal profile size.