Entropy-Guided BIST Instruction Set Compression for Auto-CP Embedded Flash Testing

Embedded Flash chip probing (CP) testing in an automotive Microcontroller Unit (MCU) involves long test flows and numerous test items. Conventional BIST-based testing relies on step-by-step Automated Test Equipment (ATE) instruction configuration, status polling, and result readout, causing considerable ATE interaction overhead that grows with the number of test items. This paper proposes an Auto-CP Built-In Self-Test (BIST) method with entropy-guided two-stage instruction set compression and on-chip autonomous scheduling for embedded Flash CP testing. Unlike conventional lossless compression that operates directly on raw instructions, the proposed method uses information entropy to quantify instruction redundancy and decomposes the original instruction stream into reusable instruction templates and a sequence scheduling stream. Structural compression removes repeated long instruction fields, while Huffman lossless coding shortens high-frequency symbols. On-chip decoding and scheduling logic then enable the ATE to load the compressed test program once and read the final results, eliminating step-by-step control of each test item. For a 40 nm 1 MB embedded Flash CP test at 15 MHz using an Advantest 93000 ATE, Auto-CP reduces the measured total CP test time from 42.65 s to 36.25 s, i.e., by 15%. The average ATE overhead ratio is lowered from 26% to 13%. The results show that the proposed method effectively reduces the ATE interaction overhead and improves the embedded Flash mass production CP test efficiency.