System-level verification of a modem product involves ensuring both the hardware and firmware work correctly and that the product meets signal performance requirements at low cost. In many ways, the firmware problem is harder - or at least more open-ended.We discuss a development methodology based on automatic generation and reusable components that has been used to implement several generations of software-defined radio (SDR) modem SOCs. Automation both ensures consistency between models and tools and enables fast turnaround when something changes.