A Software-Based Self-Test methodology for on-line testing of processor caches

Nowadays, on-line testing is essential for modern high-density microprocessors to detect either latent hardware defects or new defects appearing during lifetime both in logic and memory modules. For cache arrays, the flexibility to apply online different March tests is a critical requirement. For small memory arrays that may lack programmable Memory Built-In Self-Test (MBIST) circuitry, such as L1 cache arrays, Software-Based Self-Test (SBST) can be a flexible and low-cost solution for on-line March test application. In this paper, an SBST program development methodology is proposed for online periodic testing of L1 data and instruction cache, both for tag and data arrays. The proposed SBST methodology utilizes existing special purpose instructions that modern Instruction Set Architectures (ISAs) implement to access caches for debug-diagnostic and performance purposes, termed hereafter Direct Cache Access (DCA) instructions, as well as, performance monitoring mechanisms to overcome testability challenges. The methodology has been applied to 2 processor benchmarks, OpenRISC and LEON3 to demonstrate its high adaptability, and experimental comparison results against previous contributions show that the utilization of DCA instructions significantly improves test code size (83%) and test duration (72%) when applied to the same benchmark (LEON3).