Low Latency Retimer with Sideband Protocol Monitoring
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Solution Overview
Problem
Current interconnect architectures in computing systems face challenges in meeting the increasing demand for high-performance communication between processors and devices, particularly in server environments, where power consumption and latency become significant issues as data rates and complexity grow.
Innovation Solution
The implementation of a multi-protocol capable low-latency retimer with a sideband channel for normal traffic and minimal protocol-specific logic, allowing it to support protocols like PCI Express and Ultra Path Interconnect (UPI), which extends the reach between CPU and downstream devices or processor nodes while minimizing latency through partial protocol-specific equalization and link training.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If traditional retimers are used to extend channel length, then the reach between processors and devices is increased, but latency increases and protocol compatibility is lost
Solution Approach 1:
The retimer device is segmented into multiple functional blocks: a receive block that separates incoming signals into data and clock components, a buffer block that stores data bits, and a transmit block that reconstructs signals. This segmentation allows independent optimization of each function to minimize overall latency while extending channel reach.
Solution Approach 2:
The retimer performs preliminary equalization and signal conditioning before retransmission. By pre-processing the signal with protocol-specific equalization coefficients and preparing data in advance in buffer blocks, the system minimizes processing delays during actual data transmission, thus reducing latency while maintaining signal integrity over extended channels.
2Adaptability or versatility
If full protocol-specific logic is implemented in retimer, then protocol compatibility is improved, but device complexity and power consumption increase
Solution Approach 1:
The retimer is designed with universal functional blocks that can handle multiple protocols. The receive block, buffer block, and transmit block are protocol-agnostic structures that can be configured for different protocols through programmable equalization coefficients and control registers, allowing one device to serve multiple protocol families without requiring separate dedicated logic for each.
Solution Approach 2:
Instead of implementing complete protocol stacks, the retimer implements only the essential protocol-specific functions needed for signal equalization and timing recovery. This partial implementation approach provides sufficient protocol compatibility for high-speed interfaces while keeping the device complexity and power consumption manageable by omitting unnecessary protocol layers.
3Reliability
If data bits are buffered for clock recovery, then signal integrity is improved, but latency increases
Solution Approach 1:
The retimer uses periodic clock signals to control data buffering and retrieval operations. By synchronizing buffer operations with the periodic clock edge, the system achieves reliable clock recovery and signal integrity while minimizing buffering delay through efficient periodic data movement rather than continuous or premature buffering.
Solution Approach 2:
The system dynamically adjusts buffering parameters such as buffer depth and retrieval timing based on signal conditions and protocol requirements. By changing these parameters adaptively, the retimer optimizes the balance between signal integrity (requiring adequate buffering) and latency (requiring minimal buffering), achieving both goals under different operating conditions.
Data Source
AI summary
A retimer device receives a first signal from a first device and regenerates the first signal to send to a second device. The retimer further receive a second signal from the second device and regenerates the second signal to send to the first device, where the first device includes a processor device. The retimer includes a sideband interface to connect to the first device and further includes protocol logic to monitor the first signal, determine that the first signal includes a pattern defined in a protocol to identify a protocol activity, and participate in performance of the protocol activity using the sideband interface.