Top 10 Semiconductor Interview Questions on PCIe and CXL for 2025

Here’s a curated list of  Top 10 Semiconductor Interview Questions on PCIe and CXL for 2025, reflecting industry trends and technical depth:

1. PCIe Architecture & Evolution  

Q: Explain the key improvements in PCIe 6.0 over PCIe 5.0, including encoding, bandwidth, and use cases. How does PAM4 signaling affect signal integrity challenges?  

2. CXL Fundamentals  

Q: CXL builds on PCIe but adds protocols like CXL.cache and CXL.mem. Describe how these protocols enable memory pooling and coherency in heterogenous systems (e.g., CPUs, GPUs, accelerators).  

3. Coexistence of PCIe and CXL  

Q: How does CXL leverage PCIe’s physical layer, and what modifications are required to enable CXL.mem or CXL.cache on existing PCIe 5.0/6.0 infrastructure?  

4. Coherency & Memory Semantics  

Q: Compare cache coherency in CXL with traditional approaches like snooping or directory-based coherency. Why is CXL particularly suited for disaggregated memory architectures?  

5. Error Handling & Reliability  

Q: PCIe uses LCRC (Link CRC) and retry mechanisms for error recovery. How does CXL enhance error handling for memory-semantic operations, especially in large-scale data centers?  

6. Power Management  

Q: Discuss PCIe’s L0s/L1 power states and how CXL devices manage power while maintaining low-latency cache-coherent links. What challenges arise in dynamic power scaling?  

7. High-Speed Design Challenges  

Q: PCIe 6.0 uses PAM4 and FLIT (Flow Control Unit) encoding. What signal integrity issues arise at 64 GT/s, and how do forward error correction (FEC) and equalization mitigate them?  

8. Protocol Layers & Stack  

Q: Map the PCIe transaction, data link, and physical layers to CXL’s protocol stack. How does CXL.cio differ from native PCIe transactions?  

9. Use Cases & Industry Adoption  

Q: Why are CXL-based memory expanders gaining traction in AI/ML workloads? Compare CXL’s role in composable infrastructure vs. NVLink or CCIX.  

10. Debugging & Future Trends  

Q: How would you troubleshoot a PCIe/CXL link training failure? What tools (e.g., protocol analyzers, BERT scopes) are critical for validating CXL 3.0’s support for fabric-attached memory?  

Bonus: Emerging Standards  

Q: Predict how PCIe 7.0 (2025+) and CXL 3.0/4.0 might address challenges like thermal management, latency reduction, and scalability for zettascale computing.  

These questions test both foundational knowledge (e.g., protocol layers, coherency) and cutting-edge topics (e.g., PAM4, composability) critical for roles in interface IP design, validation, or system architecture. 

Candidates should emphasize hands-on experience with high-speed SerDes, coherency protocols, and industry trends like AI-driven memory expansion.