Pci Express Spec [cracked] →
The PCIe specification is now a physical transport for higher-level coherence protocols. 1.1/2.0/3.0 builds directly atop PCIe 5.0/6.0 electrical and PHY layers. CXL’s three protocols (CXL.io, CXL.cache, CXL.mem) extend PCIe’s transaction layer to support cache coherency between CPUs and accelerators/GPUs/FPGAs.
The specification includes rigorous compliance checklists: pci express spec