The traditional method of developing electronic systems, especially complex low-production systems, has been to do a careful design and then build and refine a hardware prototype. But beyond a certain level of complexity, a level which, for example, digital generators for flight simulation have clearly passed, this method of hardware refinement is not practical, and a development methodology that leads to a much greater level of design certainty should be adopted. The method proposed comprises high level language software emulation of algorithms, gate level verification of logic designs, a staged system build up that couples emulations with real hardware, and a comprehensive system of diagnostics. The diagnostic system supports both hardware design verification and system maintenance.