Towards Reliable Systems: A Scalable Approach to AXI4 Transaction Monitoring

In safety-critical SoC applications such as automotive and aerospace, reliable transaction monitoring is crucial for maintaining system integrity. This paper introduces a drop-in Transaction Monitoring Unit (TMU) for AXI4 subordinate endpoints that detects transaction failures including protocol violations or timeouts and triggers recovery by resetting the affected subordinates. Two TMU variants address different constraints: a Tiny-Counter solution for tightly area-constrained systems and a Full-Counter solution for critical subordinates in mixed-criticality SoCs. The Tiny-Counter employs a single counter per outstanding transaction, while the Full-Counter uses multiple counters to track distinct transaction stages, offering finer-grained monitoring and reducing detection latencies by up to hundreds of cycles at roughly 2.5x the area cost. The Full-Counter also provides detailed error logs for performance and bottleneck analysis. Evaluations at both IP and system levels confirm the TMU's effectiveness and low overhead. In GF12 technology, monitoring 16-32 outstanding transactions occupies 1330-2616 μ m2 for the Tiny-Counter and 3452-6787 μ m2 for the Full-Counter; moderate prescaler steps reduce these figures by 18-39 % and 19-32 %, respectively, with no loss of functionality. Results from a full-system integration demonstrate the TMU's robust and precise monitoring capabilities in safety-critical SoC environments.