Measuring the effectiveness of ISO26262 compliant Self Test Library

Frederico Pratas, Thomas Dedes, Andrew Webber, Majid Bemanian, Itai Yarom


Automotive SoCs are constantly being tested for correct functional operation, even long after they have left fabrication. The testing is done at the start of operation (car ignition) and repeatedly during operation (during the drive) to check for faults. Faults can result from, but are not restricted to, a failure in a part of a semiconductor circuit such as a failed transistor, interconnect failure due to electromigration, or faults caused by soft errors (e.g., an alpha particle switching a bit in a RAM or other circuit element). While the tests can run long after the chip was taped-out, the safety definition and test plan effort is starting as early as the specification definitions. In this paper we give an introduction to functional safety concentrating on the ISO26262 standard and we touch on a couple of approaches to functional safety for an Intellectual Property (IP) part such as a microprocessor, including software self-test libraries and logic BIST. We discuss the additional effort needed for developing a design for the automotive market. Lastly, we focus on our experience of using fault grading as a method for developing a self-test library that periodically tests the circuit operation. We discuss the effect that implementation decisions have on this effort and why it is important to start with this effort early in the design process.