We have developed an application-driven methodology for implementing parallel and heterogeneous programmable platforms. We deploy our flow for network access platforms where we have to trade off flexibility against costs and performance. Our methodology therefore focuses on characterizing the application domain as early as possible. With this input, we can narrow the design space to one major design trajectory that starts with the most flexible solution and refines the platform architecture systematically to meet performance and costs constraints. Our flow includes an efficient path to implementation in hardware and software. The software implementation framework takes a modular application description and generates code for embedded processors that can easily be ported to different platforms and used for profiling. Different communication architectures, co-processors, and specializations of programmable processing elements can be derived from profiling results to affect the platform hardware. A DSL Access Multiplexer (DSLAM) is used as an example throughout the paper to depict the different phases of our design process.