What you'll learn

Outstanding transactions hide latency — ordering rules determine whether the results are correct.

• Outstanding = accepted work with an unfinished completion obligation at the named boundary.

• Same ID ordered, different IDs may reorder — protocol and bridge dependent.

• Publication and fences must satisfy the selected language/OS, architecture and device contracts.

• Scoreboard and verification must model legal reorder, not assume strict order.

Connection

Ordering defines AXI ID rules, ACE barriers, PCIe relaxed ordering, and CPU memory models.

Key diagram

Choose the correct response queue

Study this topic

1. Concepts — rules and mental models

2. Integration — system contracts

3. Debug — trace the first divergence

4. Deep Dive — extend the mechanism

5. Worked Examples — reconstruct the reasoning

6. Interview — explain and defend your answer