Towards ISO 26262-compliant Vector Processors: Combining STLs and LBIST

Vector Processing Units (VPUs) are increasingly integrated into safety-critical automotive SoCs to accelerate general-purpose and Machine Learning inference workloads, making their functional safety essential in compliance with ISO26262. This work explores the effectiveness of common safety mechanisms (SMs) for permanent faults in a VPU (i.e., Software Test Libraries, or STLs, Logic Built-In Self-Test, or LBIST, and their combination). Without any SM, the VPU achieves a Single Point Fault Metric (SPFM) of only 1.2%, confirming the necessity of suitable SMs. STLs alone satisfy the SPFM threshold for ASIL B with values of 95.43%, 96.38%, and 95.98% for 2-, 4-, and 8-FU VPU configurations, respectively, while LBIST alone meets the SPFM target for ASIL D at 2-FU (99.36%) and 8-FU (99.11%), and ASIL C at 4-FU (98.69%). The hybrid approach meets the SPFM target for ASIL~C across all configurations, with up to 11% lower area overhead and up to 66% shorter minimum testing interval than LBIST alone, making it a practical solution for continuous in-field automotive deployment.