galsC: A Language for Event-Driven Embedded Systems

Elaine Cheong and Jie Liu

Memorandum No. UCB/ERL M04/7
20 April 2004
Electronics Research Laboratory
College of Engineering
University of California, Berkeley 94720




We introduce galsC, a language designed for programming event-driven embedded systems such as sensor networks. galsC implements the TinyGALS programming model. At the local level, software components are linked via synchronous method calls to form actors. At the global level, actors communicate with each other asynchronously via message passing, which separates the flow of control between actors. A complementary model called TinyGUYS is a guarded yet synchronous model designed to allow thread-safe sharing of global state between actors via parameters without explicitly passing messages. The galsC compiler extends the nesC compiler, which allows for better type checking and code generation. In galsC programs, all inter-actor communication, actor triggering mechanisms, and access to guarded global variables are automatically generated by the compiler. Having a well-structured concurrency model at the application level greatly reduces the risk of concurrency errors, such as deadlock and race conditions. The galsC language is implemented on the Berkeley motes and is compatible with the TinyOS/nesC component library. We use a multi-hop wireless sensor network as an example to illustrate the effectiveness of the language.