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CXL 4.0 Introduction
The exponential growth of artificial intelligence (AI) and high-performance computing (HPC) has ushered in a new era of data-centric innovation. At the heart of this transformation lies Compute Express Link (CXL) 4.0, an open standard designed to deliver unprecedented speed, scalability, and flexibility for next-generation data centers. Building on the robust foundation of PCI Express (PCIe), CXL 4.0 introduces a suite of enhancements that directly address the demands of modern cloud, AI, and HPC workloads—making it a critical enabler for breakthrough performance and efficiency.
What’s New in CXL 4.0
Driving Next-Gen AI and HPC, CXL 4.0 marks a significant leap from its predecessors, aligning with PCIe 7.0 and doubling the data rate to a staggering 128 GT/s per lane. This advancement empowers organizations to scale AI training clusters, real-time analytics, and HPC simulations with lower latency and higher bandwidth. For example, hyperscale cloud providers now deploy CXL 4.0-enabled memory expanders to pool resources across thousands of nodes, optimizing both cost and compute efficiency.
Enhanced Features for Modern Workloads Key innovations in CXL 4.0 include:
- Higher Bandwidth: Doubles data rate to 128 GT/s per lane for improved scalability and performance.
- Backward Compatibility: Supports CXL 3.0 and earlier versions while enabling new feature negotiation.
- Retimers: Up to four CXL-aware retimers supported.
- Bandwidth Throttling: IO bandwidth can drop to 32 GT/s for slower devices while maintaining 128 GT/s for cache/memory traffic.
- Port Aggregation with Bundled Ports: Introduces a well-defined Port Aggregation strategy called Bundled Ports, which combines multiple physical CXL ports into a single logical port. Each bundle includes at least one Standard Port and one or more lightweight Streamlined Ports, delivering higher aggregate bandwidth than any single port can achieve.
- Streamlined Ports: Simplifies chip design through Streamlined Ports, which eliminate support for 68B flits. This design choice significantly reduces hardware complexity, resulting in smaller, more efficient implementations.
- Fabric Management: Advanced features for host-to-host, better switch support, and improved device discovery.
- Coherency: Enhanced protocols for robust cache and memory sharing.
- Security: Stronger IDE and fabric-level protections for complex topologies.
- Verification Support: Clear compliance guidelines and robust test strategies to validate new features and ensure interoperability.
Synopsys CXL4.0 SS Verification IP
Synopsys continues to lead innovation with the industry’s first commercially available CXL 4.0 Verification IP (VIP). This comprehensive solution supports the full 128 GT/s data rate, IO throttling, and streamlined port negotiation, equipping designers to validate and optimize their products for the future. VIP’s intuitive APIs and migration paths from CXL 3.0 and PCIe 7.0 ensure rapid adoption and verification closure, enabling faster time-to-market for next-gen AI and HPC platforms. The solution includes:
- Native System/Verilog UVM architecture that allows seamless integration.
- Highly configurable and scalable architecture for multiple verification requirements.
- Built-in protocol checks that adherence to the specification.
- Debug features that include trace files, debug ports and verbosity-controlled messaging.
Conclusion
As AI and HPC workloads evolve, CXL 4.0 stands as a foundational technology driving new levels of performance, efficiency, and scalability. Synopsys, a key contributor to the CXL 4.0 specification, leads the way with its industry-first CXL 4.0 VIP. This solution enables designers to harness these advancements with confidence, future-proofing their solutions for tomorrow’s data-driven challenges. Stay tuned for upcoming enhancements as CXL 4.0 continues to shape the future of intelligent computing.
Synopsys is partnering with early customers and collaborators to enhance the standard architecture for their next-generation designs, incorporating new features now available with the latest specifications.
Synopsys VIP is natively integrated with the Synopsys Verdi® Protocol Analyzer debug solution as well as Synopsys Verdi® Performance Analyzer. Running system-level payload on SoCs requires a faster hardware-based pre-silicon solution. Synopsys transactors, memory models, hybrid and virtual solutions based on Synopsys IP enable various verification and validation use-cases on the industry’s fastest verification hardware, Synopsys ZeBu® emulation and Synopsys HAPS® prototyping systems.
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