As new compute-intensive machine learning (ML) and artificial intelligence (AI) workloads drive servers to adopt faster PCI Express® 5.0 Links, lower-latency cache-coherent protocols like Compute Express Link™ (CXL™), and a dizzying array of memory, storage, AI processor (AIP), smart NIC, FPGA, and GPU elements, so too is heterogeneous computing pushing the need for blazing-fast networks to interconnect the resources.
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PCI Express® 5.0 Architecture Channel Insertion Loss Budget
The upgrade from PCIe® 4.0 to PCIe 5.0 doubles the bandwidth from 16GT/s to 32GT/s but also suffers greater attenuation per unit distance, despite the PCIe 5.0 specification increasing the total insertion loss budget to 36dB. After deducting the loss budget for CPU package, AIC, and CEM connector, merely 16dB system board budget remains. Within the remaining budget, engineers need to consider safety margin for board loss variations due to temperature and humidity.
Simulating with Retimers for PCIe® 5.0
The design solution space for high-speed serial links is becoming increasingly complex with increasing data rates, diverse channel topologies, and tuning parameters for active components. PCI Express® (PCIe®) 5.0, at 32 GT/s, is a particularly relevant example of an application whose design solution space can be a daunting problem to tackle, given the performance-cost requirements of its end equipment. This paper is intended to help system designers navigate these design challenges by providing a how-to guide for defining, executing, and analyzing system-level simulations, including PCIe 5.0 Root Complex (RC), Retimer, and End Point (EP).
PCI Express® Retimers vs. Redrivers: An Eye-Popping Difference
A redriver amplifies a signal, whereas a retimer retransmits a fresh copy of the signal. Retimers provide capabilities such as PCIe® protocol participation, lane-to-lane skew compensation, adaptive EQ, diagnostics features, etc. Therefore, retimers particularly address the need for reach extension in PCIe 4.0 & PCIe 5.0 systems, where increased number of PCIe slots, multiconnectors, and long physical topologies lead to signal integrity (SI) challenges.
The Impact of Bit Errors in PCI Express® Links: The Painful Realities of Low-Probability Events
PCIe 5.0 ushers in the era of >1Tbps of data bandwidth between two PCIe nodes, and noticeably greater Link Errors and DLLP Retries are likely to occur. By reducing insertion loss (shorter trace, better material, connectors, etc.) or adding retimers to some topologies, system designers can minimize system-level headaches with a target of 1E-17 or lower BER.