HUSTLE: A Hardware Unit for Self-test-Libraries Efficient Execution

Online testing of computer systems is crucial in contexts such as the safety-critical domain, where the software is usually made of functional code, which is the code implementing the application-specific functionalities, and non-functional code, which implements auxiliary functionalities, e.g., test routines. By periodically running a test routine it is possible to satisfy the high dependability requirements mandated by regulators, and defined in safety standards such as ISO26262, IEC61508, and CENELEC EN 5012X. Self-Test Libraries (STLs) are a form of software-based self-test, widely used in safety-related applications. The main drawback of this safety mechanism is the overhead imposed on the execution of the functional code, and reducing this overhead is a well-known challenge in research. We propose here HUSTLE, a Hardware Unit for STL Efficient execution, which can be integrated into the chip design with no modification to the CPU’s internal logic. We also propose a scheduling mechanism that allows HUSTLE to efficiently execute self-tests, by exploiting the CPU’s idle time. This is achieved by storing test code in a separate memory and sending instructions to the CPU, bypassing the Instruction Cache, thus allowing to reduce the overall execution time and the cache interference of STL, while CPU utilization increases.