DO-178B COSTS vs. BENEFITS
DO-178B has increasingly evolved into the de-facto standard for commercial avionics, then military avionics, and now general aerospace electronics. And the new DO-178C is on the horizon. DO-178B requires planning, consistency, determinism, thorough documentation and testing, and proof of the preceding attributes. DO-178B relies upon testing to verify and validate avionics quality. However, avionics quality comes from a quality process, design, and implementation, not just from testing.
The DO-178B (software) and DO-254 (hardware) standards presume that hardware and software must operate in harmonic unison, each with proven reliability. Previously, hardware was considered “visible” and tested at the systems level with integrated software; hence hardware was exempt from DO-178B quality attributes. But that exemption resulted in functionality being moved from software to hardware for the purpose of avoiding hardware certification. Also, hardware complexity has evolved such that hardware is often as complex, or more so, than software due to the embedded logic within the PLDs, ASICs and FPGAs. Now, everyone recognizes that hardware and software comprise an inextricable chain with the quality equal to that of the weakest link, hence the mandate to also apply DO-254 to avionics hardware. The weakest links are continually removed through the avionics certification evolution.
In DO-178B “software” pertains to all drivers, BSP, RTOS, libraries, graphics, and the application software, i.e. any executable which is loaded into memory during execution. Software testing means ensuring that the lowest level detailed requirements are accurately implemented, paths are covered according to their criticality level, and full traceability is provided. Increasingly, tools are being used to automate DO-178B processes. For example, almost all DO-178 projects today use a commercial traceability tool for avionics software. While traceability tools are not formally required, virtually every DO-178B compliant project uses them to meet DO-178B’s top-to-bottom and bottom-to-top traceability. While DO-178B does not require such tools (you can always provide traceability manually), a DO-178B compliant traceability tool greatly reduces the cost of compliance.