Using assertions to satisfy DO-254 Elemental Analysis

Abstract

RTCA DO-254 [1], the design assurance guidelines for airborne electronic hardware development, requires additional advanced verification techniques for design assurance level (DAL) A or B devices. “Elemental Analysis” is most commonly chosen, and is intended to ensure requirements-based tests are sufficiently exercising the “elements” of a design, thus providing a measure of verification completeness. For HDL-based designs, this is typically performed by collecting code coverage metrics during the simulation of these requirements-based tests, thus identifying which portions of the HDL code have not been exercised. While this is a commonly accepted approach, using code coverage alone presents a variety of drawbacks when viewed as a metric for verification completeness. Another technique called Assertion Based Verification (ABV) provides a more thorough mechanism of judging verification completeness, and additionally can provide credit toward Robustness testing. ABV utilizes proven techniques that have been widely used across a variety of segments of the electronics industry for over 20 years. Today's ABV techniques are based on IEEE standards, and are supported by all the industry leading simulators. Yet, in the avionics industry, ABV lags in adoption. This is unfortunate because ABV can be a very powerful approach to verification when used as part of a sound overall verification methodology, providing a much more thorough verification and coverage assessment than code coverage alone, and with only modest additional effort by the design and/or verification teams. This paper discusses DO-254 and what it requires for verification (including advanced methods for DAL A/B designs), explains the original intent of Elemental Analysis, the way it is typically satisfied today with code coverage, introduces ABV, and proposes a method for using this technique to not only satisfy Elemental Analysis but also to support a systematic approach to satisfying a claim of Robustness testing.