Design and Analysis of Testable Mutual Exclusion Elements

Mutual exclusion elements (MUTEXes) are fundamental components of asynchronous arbiters and are particularly critical to ensure metastable signals are properly filtered before reaching the arbiter outputs. However, despite their importance, the testability of these circuits is typically limited to functional testing. This paper discusses why this is not sufficient and addresses testability issues in both full-custom and standard-cell implementations. In particular, it proposes two new testable implementations that not only ensure improved coverage for single stuck-at faults but also enable testing the filtering of metastable signals. Additionally, this article quantifies the cost of the testable designs by comparing them to similar traditional designs in terms of area, power and metastability resolution time. Results show the proposed optimizations do increase area and power but have small impact on performance.